US3500455A - Light responsive electrical lamp dimming means - Google Patents

Description

March 10, 1970 S. L. ROSS ETAL LIGHT RESPONSIVE ELECTRICAL LAMP DIMMING MEANS Filed July 5. 1968 2 Sheets-Sheet 1 l s Pl H7 ma m M i March 10, 1970 s. l.. Ross ErAl. 3,500,455

LIGHT RESPONSIVE ELECTRICAL LAMP DIMMING MEANS s E i0 t $60 "I /Q`26 4a Z0 frm/HL P055 JoffP/f ZF/r PAM/m 57 i 90 /oa //0 /272 50 a #0L mcisma MMP f f ffm f4 7 7 RNEY United States Patent O U.S. Cl. 315-149 22 Claims ABSTRACT OF THE DISCLOSURE A light responsive electrical lamp dimming means is shown which is adapted for use with an alternating current voltage source energized traffic control system and wherein the dimming means proportionally varies intensity of a traffic signal lamp between a high intensity level and a predetermined low intensity level as a function of sensed background illumination. In one embodiment, a light responsive electrical lamp dimming means includes a controllable bi-directional conducting means which is controlled by a triggering means which in turn is responsive to a background illumination sensing means adapted to detect changes in background illumination in the vicinity of a lamp for controlling the triggering means which varies conduction of the bi-directional conducting means between a first state and a second state in proportion to sensed changes in background illumination between a bright level to a preselected dark level.

Electrical lamp dimming circuits which selectively switch a rectifier into and out of a circuit for changing the intensity of a lamp are known; see for example, Patent Nos. 2,896,125; 3,009,071; 3,028,525 and 3,037,146. In such electrical lamp dimming circuits, the rectifier, when connected into the energizing circuit, causes the lamp to operate at a preselected minimum intensity level. When the rectifier is selectively switched out of the circuit, the lamp is permitted to be energized by the energizing circuit at a normal intensity. Thus, by manually switching the rectifier into and out of the energizing circuit, the lamp intensity is abruptly changed between one of two discrete intensity levels.

The electrical lamp switching mechanism disclosed in Patent No. 2,896,125 is typical. In Patent No. 2,896,125, a bypass circuit is connected in parallel to the rectifier. The bypass circuit includes a switching mechanism having a switching member which, when manually connected in parallel to the rectifier, enables the energizing circuit to apply normal voltage to the lamp thereby operating the lamp at a normal intensity level. When the switching member is manually switched to an open-circuit position, the rectifier is rendered conductive for approximately onehalf of an alternating current voltage cycle. The power applied to the lamp is approximately one-half of its original value and the lamp is then abruptly dimmed to a lower intensity level which is equal to about 25 to 30 percent of the normal intensity level when the lamp is operated at normal voltage.

Another known system for selectively dimming the lumen output of an electrical lamp is shown in Patent No. 3,061,744. The lamp dimming circuit utilizes a fourlayer diode, such as a Zener diode, in combination with a half-wave rectifier connected in a back-to-back relationship. Such a combination permits lmanual control of the voltage applied to a lamp such that the lumen output thereof can be selectively varied from substantially zero percent to 100 percent.

In addition to the above, Patent No. 3,061,744 also 3,500,455 Patented Mar. 10, 1970 ICC discloses circuitry for triggering the gate of a siliconcontrolled rectifier (SCR). Also, this circuitry includes switching means for selectively switching a diode into and out of parallel relationship with the silicon-controlled rectifier in order to dim the lumen output of the lamp over a range of between zero and percent.

Use of SCRs as a continuously variable dimmer switch for controlling the intensity level of a lamp at a manuallyset intensity level is disclosed in U.S. Patent Nos. Re. 26,119 and 3,103,618'. For example, in Patent No. 3,103,618, a variable phase shift circuit is used to provide a controllable gating signal for the gate electrode of the SCR in response to a manual setting of a variable resistor in the phase control circuit.

Light responsive switching circuits for selectively energizing and de-energizing a lam-p as a function of ambient light illumination are known in the art. For example, in Patent Nos. 3,088,051 and 3,210,611, a light responsive element is used to control actuation of a relay by means of a transistor switching circuit for selectively energizing a lamp. In the circuits in each of the Patent Nos. 3,088,051 and 3,210,611, the lamps are abruptly switched between two different levels of illumination; namely, substantially 100 percent lumen output when the lamps are energized and zero percent lumen output when the lamps are de-energized.

Use of photocells, as bistable switching devices, in combination with triggering circuits for controlling phase angle of conduction of a bidirectional gated semiconductor device, such as a triac are known. For example, the circuit of FIGURE 19 appearing at page 12 in G E. Application Note Number 200.35 dated March 1966 discloses use of a photocell as part of a firing circuit for a unijunction transistor which in turn triggers a triac which also is controlled by a small pilot SCR which gives continuous drive to the gate following triggering of the triac until the current load is high enough for the triac to latch. In this circuit of FIGURE 19, the photocell is merely utilized as a bisable control device having a finite switching time.

Also, FIGURES 24 and 25 on page 15 of the same G.E. Application Note cited above utilize a photocell as a bistable switch for controlling triggering of a triac. In each of the above uses of photocells in the triggering circuits, an extremely small change in foot-candle illumination, say in the order of 2 foot-candles or so, causes the photocell to abruptly change from a high resistance (dark level) to a low resistance in the order of 2000 ohms when the photocell is illuminated. Thus, the abrupt switching -characteristic of the photocell vbistable control device is abruptly responsive to the illumination directly incident upon the photocell and is therefore not capable of being used to proportionally control triggering of the triac over a wide range of illumination.

One primary disadvantage of the prior art devices, including those discussed hereinabove, resides in that a light sensing means heretofore has been used for selectively actuating and deactuating a lamp in response to l ambient illumination levels in the vicinity of 'the light sensing means. Further, the electrical lamp dimming circuits .of the prior art, including those cited above, can be selectively controlled only in response to a manual setting of a dial or its equivalent.

The present invention overcomes the disadvantage of the prior art devices, including those set forth above, by a unique light responsive electrical lamp dimming system and means which proportionally controls the intensity of a lamp between a high intensity level and a predetermined low intensity level as a function of background illumination in the vicinity of the lamp.

The prior art devices which utilize a light sensing means have apparently neither recognized the advantage of nor solved the problem of selectively controlling lamp intensity in proportion to background illumination. In the embodiment disclosed herein, the background illumination which impinges on the light sensing means, such as, for example, a photocell, is selectively transmitted so as to vary the light sensing means characteristics in proportion to the background illumination.

In addition to the above teachings, the present invention also teaches that the proportional dimming characteristics of the light responsive electrical lamp dimming circuit can be preset such that when the background illumination decreases below a preselected dark level, the intensity of the controlled lamp can be fixed at a predetermined low intensity level.

One important use of a light responsive electrical lamp dimming means of the present invention is in a traffic control system. One problem encountered by traffic control engineers in designing traffic signal systems is to match the intensity level or lumen output of a traffic signal lamp at a level which is compatible with the background illumination at an intersection served by the traffic lighting system. For example, around sunset on a relatively clear day, a driver travelling in a westerly direction normally has the sun directly in his eyes. When a driver travelling in a westerly direction on such a day approaches a traffic signal section having a setting sun directly therebehind as the background illumination, he may not be able to distinguish which traffic indication is being displayed by the traffic signal lamp servicing the lane in which he is travelling. One reason why a driver cannot sometimes distinguish the signal condition for his lane is that the traffic signal lamp has an intensity level which is equal to or lower than the intensity level of background illumination; namely, the setting sun.

One way of solving a problem presented by a setting sun as described above is to utilize a traffic signal lamp having a high intensity .or lumen output. This would require increasing the intensity level of the lamp such that it is substantially brighter relative to the background illumination, e.g. the setting sun, than the intensity level of the lamp when the background illumination is dark. After the sun has set, the background illumination is substantially reduced in level. The background illumination may be a dark sky or could be derived from artificial lighting, such as for example fiuorescent signs, overhead street lights and the like. In either case, if the traffic signal lamp intensity was increased so as to be brighter to compensate for the background illumination including the setting sun, the lamp would be extremely bright in a dark background illumination. A driver approaching an intersection under such a condition could be blinded by the bright or high intensity trafiic signal lamp.

The advantages and desirability of controlling the intensity of the traffic signal lamp such that its intensity is at a high level when the background illumination in the vicinity of the lamp is at a bright level and its intensity is at a lower level when the background illumination is at a lower level is readily apparent.

Many attempts have been made, without a great deal of success, to match or correlate the intensity of a traffic signal lamp with its associated background illumination. At intersections where the sky and other background illumination are at a relatively normal level during the day and are at a dark level after sunset, traffic signal lamps are used which have a wattage rating less than that required by traffic highway standards. A lower wattage traffic signal lamp having a dark background illumination is not apt to blind a motorist travelling in a vehicle toward the intersection being serviced by the traffic signalling system.

Another prior art solution to this problem has been to utilize a transformer having a normal voltage winding and a separate bucking winding for supplying voltages to the traffic signal lamp. When a reduced voltage is 4 Y required, the bucking winding is energized which in turn generates an opposite magnetic eld which results in a reduced voltage being applied to the traffic signal lamps. The reduced voltage, in turn, operates the lamps at a reduced intensity level. Use of transformers with separate bucking windings results in a traffic signal light dimming circuit having several disadvantages, such as for example being relatively expensive, being limited in range of control, being bulky and heavy and being difficult to install in existing traffic signal intersections.

One advantage of the present invention is that a unique and relatively inexpensive light responsive electrical lamp dimming means is provided which is capable of selectively varying the intensity of a single traffic signal in a traffic signal face. The intensity of the traffic signal lamp can be varied between a high intensity level and a predetermined low intensity level in proportion to the background illumination varying between a bright level and a preselected dark level.

Another advantage of the present invention is that the light responsive electrical lamp dimming means can be utilized to proportionally control the intensity of (a) a single traffic signal lamp or indication in a selected traffic signal face, (b) the trafiic signal lamps or indications which are identical and in the same phase wherein each lamp is located in a different traffic signal face, (c) the traffic signal lamps or indications in a single traffic signal face, or (d) the traffic signal lamps or indications in a plurality of traffic signal faces in the same phase.

Another advantage of the present invention is that side glow can be effectively reduced and controlled from a display device adapted for use as a traffic signal section. One such display device includes a condensing display lens defining a viewing surface, lighting means for providing modifiable diffuse illumination of the lens from points substantially at the focus of the lens and aperture means disposed substantially at the focus which outlines a predetermined viewing area, such as for example a selected traffic lane, as described in a copending patent application of Roger H. Appledorn, Ser. No. 571,639, having a common assignee. Normally, such side glow is a function of the intensity of the trafiic signal lamp and is most noticeable when the traffic signal lamp intensity is substantially greater than the intensity of the background illumination. Thus, dimming of the traffic signal lamp is in proportion to the sensed background illumination is effective to reduce and control such side glow.

An other important use of the light responsive electrical lamp dimming means of the present invention is that the intensity of the trafiic signal lamps in traffic signal faces of different phases, but which are facing in a preselected direction, can be selectively dimmed. For example, during the sunset conditions described above, a motorist travelling eastbound with the sun behind him would encounter a low level background illumination such that a bright or high intensity traffic signal lamp would be blinding to the motorist.

On the other hand, a motorist travelling westbound would encounter a bright level background illumination; namely, a setting sun. In this instance, it is desirable to have the traffic signal lamps, which control the traffic moving in a westerly direction, at a high intensity level. By use of the present invention, each of the traffic signal lamps controlling the traffic moving eastbound can be operated at a lower intensity level while each of the traffic signal lamps controlling the traffic moving westbound can be operated at a high intensity level.

Another advantage of the present invention is that the intensity of any single traffic signal lamp or all of the traffic signal lamps in a given traffic signal face or faces can be separately controlled for other unusual background conditions. For example, a given traffic signal lamp may have a low level background illumination during daylight hours such that the intensity of the traffic signal lamp should be at an intensity level which is less than normal. The same traic signal lamp, or traffic signal face or faces as the case may be, could well have a background illumination which is at a brighter level during nighttime hours than daytime hours. Such a brighter background illumination level could be due to artificial street lighting, neon signs and the like. In this instance, the intensity of the traffic signal lamp in the face or faces would then be increased in intensity to compensate for the brighter background illumination.

These and other advantages of the present invention will become apparent when considered in light of the description of several embodiments set forth herein taken together with the drawing wherein:

FIGURE 1 is a diagrammatic representation, partially in block form and including a schematic diagram, illustrating a light responsive electrical lamp dimming system adapted for use in a traffic signal system for controlling an intersection;

FIGURE 2 is a schematic diagram partially in block form illustrating a traffic signal face including a left turn indication wherein only the red indication in a single traffic signal face or identical indications of the same phase in other traiic signal faces is controlled by a light responsive dimming means of the present invention;

FIGURE 3 is a schematic diagram partially in block form illustrating a traic signal face including a right turn indication wherein each individual indication is controlled by a light responsive light dimming means of the present invention;

FIGURE 4 is a schematic diagram of a traffic signal section wherein all indications in all traffic signal faces of the same phase are controlled by a light responsive light dimming means of the present invention;

FIGURE 5 is a schematic diagram of one embodiment of a circuit capable of use in FIGURES 2 and 3;

FIGURE 6 is a graph illustrating the percentage light output plotted as a function of illumination of the lamp of FIGURE 5 wherein a yellow jewel is used as a light absorbing means and wherein the alternating current voltage applied to the lamp of FIGURE 5 is plotted as a function of illumination for the yellow jewel and a red jewel;

FIGURE 7 is a schematic diagram of yet a different embodiment of the present invention which is capable of use in FIGURE 4; p

FIGURE 8 is a graph of the percent light output plotted as a function of voltage across the lamp for the circuit of FIGURE 7;

FIGURE 9 is a fragmentary side cross-sectional view of a traffic signal section housing having mounted therein a packaged electrical circuit illustrated in FIGURE 5; and

FIGURE 10, which is located on the first sheet of drawing, is a fragmentary side cross-sectional view of a traffic signal section housing having mounted therein a packaged electrical circuit illustrated in FIGURE 7.

Briefly, this invention relates to a light responsive electrical lamp dimming circuit, system and means adapted to be energized from a source of alternating current for proportionally controlling of a lamp between a high intensity level and a predetermined low intensity level as a function of sensed background illumination. In addition, the electrical lamp dimming means can be used in a traffic signal control system for proportionally operating a traffic signal lamp over a range of desired operating levels of illumination.

In one embodiment, the light responsive electrical lamp dimming means includes a controllable 'oi-directional conducting means which is connected in series with the lamp to be dimmed for controlling conduction of an alternating current through the lamp. The amplitude of the voltage applied across the lamp is dependent on the voltage magnitude of the alternating current source at the time the bi-directional conducting means is rendered conductive. A triggering means is electrically connected to the bidirectional conducting means and selectively varies coriduction thereof between a first state wherein an electrical current is passed through the lamp to establish a voltage thereacross for substantially an entire portion of an alter nating current voltage cycle which operates the lamp at a high intensity level and a second state wherein an electrical current is passed through the lamp to establish a voltage thereacross4 for at least a portion of an alternating current voltage cycle which operates the lamp at the predetermined low intensity level. A `background illumination sensing means, which is adapted to detect changes in background illumination in the vicinity of the lamp, is capable of controlling the triggering means for varying conduction of the bi-directional conducting means between the first state and the second state in proportion) to sensed changes in background illumination which varies from a bright level to a preselected dark level.

FIGURE 1 illustrates diagrammatically a typical intersection of two highways, generally designated by dashed lines 12 and 14, which are serviced by a traffic signal system. The traifc signalling system illustrated herein for purposes of example comprises four traffic signal faces designated 16, 18, 20, 22v and a traffic signal controller 24. The traffic signal controller 24 is electrically connected to and controls each of the traffic signal faces 16-22 in a normal manner. Each traffic signal face is illustrated to contain three indications, generally known as red, amber and green. Normally, an incandescent traffic signal lamp and an appropriate colored lens is utilized to establish the color for the indication. In addition, of a mark, such as an arrow to indicate direction, is required, the colored lens is appropriately masked. In traffic signal face 16, the red indication is generally designated as lamp 30, the amber indication is designated as lamp 32 and the green indication is designated as lamp 34. Each of the other faces 18-22 has a similar red indication, amber indication and green indication.

In the intersection formed by crossing of highways 12 and 14, the north-south lanes are controlled by traffic signal faces 16 and 18. Traffic signal face 16 may be located in the northwest corner of the intersection while traiiic signal face 18 may be located in the southeast corner of the intersection. The placement of the traffic signal faces of FIGURE l is merely exemplary and it is contemplated that the traffic signal faces could well be located in other corners of the intersection in accordance with existing traffic signal standards. Typically, traffic signal face 16 located in the northwest corner of the intersection would be used for controlling traic in the northbound lane of highway 12 while traffic signal face 18 would be used to control traffic in the southbound lane of highway 12.

Control of traffic iiow along one street or highway is generally referred to as traffic movement. The term phase refers to the group of indications used for controlling traffic movement in a programmed sequence. The sequence of traffic movement is the programmed order in which traffic flow through the intersection is controlled, such as, for example, that vehicles are given the right-ofway to proceed in a given direction, e.g. green indication; are required to stop, e.g. red indication; or are warned of a change in traffic movement, e.g. amber indication. In FIGURE 1, one phase, which includes traffic signal faces 16 and 18, controls the traffic movement in both the northbound and southbound directions of highway 12 and a second phase, which includes traffic signal faces 20 and 22, controls the traffic movement in both the eastbound and westbound directions of highway 14. Thus, in FIGURE 1, traffic movement through the intersection is controlled in two phases.

In some intersections, traffic movement is controlled by lanes or directions thereby requiring phases for each lane or direction. For example, in FIGURE 1 (not shown), traffic signal faces 16 and 18 and 20 and 22 could be controlled by separate phases such that traflic movement is controlled in four phases.

For purpose of consistency, the use of the terms traic signal section, indication, indicators or color refers to a traffic signal lamp in combination with a colored lens to form a single light unit which together with other units form a traiiic signal face. In FIGURE 1, this corresponds to the red indication 30 which together with amber indication 32 and green indication 34 forms the traic signal face 16. Traffic signal faces 16 and 18 form a single phase as illustrated in FIGURE l. Thus, the red indications in the traffic signal faces 16 and 18 are identical indications in the same phase wherein each section is located in a different traffic signal face.

Use of the term traffic signal lamps or indicators in a plurality of traiiic signal faces in the same phase includes the indicators used in the same phase for controlling traic movement. For example, in FIGURE 1, this includes the red, amber and green indications of traffic signal faces 16 and 18.

In addition, the term traic signal lamps or indications in a single traic signal face includes one or more indication used in a standard traffic signal face. For example, in FIGURE l, this includes red indication 30, amber indication 32 and green indication 34 in traiiic signal face 16.

Traffic signal face is illustrated to be located in the northeast corner of the intersection and is adapted to control the eastbound traffic of highway 14. The traffic signal face 22 is illustrated herein in the southwest corner of the intersection and is adapted to control the westbound lane of highway 14.

In some installations, it would be possible to install more than one traliic signal face at a given corner of the intersection. For example, the traffic signal face 16 which controls the northbound lane of highway 12 could also have mounted on the same pole in a parallel aligned relationship a trafiic signal face (not shown) which is identical to traic signal face 18 and which would also be used as a second parallel control for the southbound lane of highway 12. A combination of one or more faces in a mountable assembly is generally referred to as a traffic signal head or head Additionally, other lane control signals or indications could be added to or be a traffic signal face, for example, controlled left and right turn indications, pedestrian control indications and the like.

Traffic signal faces 16 and 18 serving the northbound and southbound lanes of highway 12 respectively are electrically connected to the traffic signal controller 24 such that all of the red indications, amber indications and green indications would be energized in proper sequence. Similarly, traffic signal faces 20 and 22 would be electrically connected to traffic signal controller 24 in the manner such that the red indication, amber indication and green indication thereof would be energized in proper sequence.

One possible electrical connecting diagram is illustrated in FIGURE l for accomplishing the appropriate interconnecion between traffic signal faces 16-22 and tra'ic signal controller 24. This electrical diagram is believed to be adequately shown by FIGURE l and need not be considered in detail here.

Each of the traffic signal faces 16-22 is illustrated as having a return or neutral of each indication electrically connected to a common neutral. For example, traffic signal face 16 has the neutrals of its traiiic signal lamps in the red indication, amber indication and green indication electrically connected to a common neutral 40. Traffic signal face 18 has the neutrals of all of its traffic signal lamps of each indication electrically connected to a common neutral 42. Traffic signal face 20 has the neutrals of its traffic signal lamps in each of the indications electrically connected to a common neutral 44. Similarly, traiic signal face 22 has the neutrals of its traic signal lamps in each of the indications electrically connected to a common neutral 46. The traffic signal controller 24 is electrically connected to and energized from an electrical distribution system, which is generally designated as 48, which may be a 120 volt, 60 cycle, alternating current voltage having a system ground.

Each of the common neutrals 40-46 for traffic signal faces 16-22 respectively is electrically connected to a traffic control system having a control means, generally designated as 52, and a light sensing means, generally designated as 54. The control means 52 includes a unilaterally conducting means such as, for example, a diode 56 having its anode electrically connected to a common neutral bus bar 58. The common neutral bus bar 58 has connecting terminals, generally designated as 60. The connecting terminals 60 have common neutrals 40-60 electrically connected thereto. The cathode of diode 56 is electrically connected via a common neutral 62 back to the system ground of the electrical distribution system 48. The unilaterally conducting means, such as for example diode 56, is effectively electrically connected in series with the signal lamps and is capable of conducting electrical current therethrough through at least a portion of the alternating current cycle.

A switching means such as, for example, a relay 68 having a normally-closed contact 70 and a relay coil 72 is operatively connected to the lamp and the unilaterally conducting means such that the position of contact 70 controls conduction of the diode 5-6. This is accomplished by normally-closed contact 70 being electrically connected in parallel to the diode 56. One lead of relay coil 72 is electrically connected to the common neutral 62 while the other lead thereof is electrically connected to the light sensing means 54. When the relay coil 72 is de-energized, normally-closed contact 70 is in a closed position and selectively bypasses Or is connected in parallel to the diode S6 and conducts electrical current through the signal lamps of the indicators. When relay coil 72 is energized, the coil 72 causes the normally-closed contact to be moved to an open position and permits the diode to completely control conduction of the current through the lamps.

In this illustrated intersection of FIGURE l, the light sensing means 54 includes a photocell 76 which is responsive to the background illumination in the vicinity of the intersection. Photocell 76 has one terminal thereof electrically connected via lead 78 to the hot or energized line of the power distribution system 48. The other terminal of the photocell 76 is electrically connected to a relay coil 80 which in turn is connected to the system ground of the electrical distribution system 48. A normallyclosed contact 82 controlled by coil 80 is electrically connected before the photocell 76 to the lead 78 is also connected to a control lead 84. `Control lead 84 is in turn connected to the other terminal of relay coil 72 within the control means 52. When the background illumination in the vicinity of the intersection is at a high level, the resistance of photocell 76 is low allowing coil 80 to be actuated holding contact 82 in an open position. When the background illumination decreases below a preselected level, the resistance of the photocell 76 becomes high reducing the voltage across coil 80 thereby deactuating coil 80 -which enables contact 82 to move into its normally-closed position. When contact 82 is in its normallyclosed position, relay coil 72 has a voltage applied thereacross from lead 78 causing normally-closed contact 70 to be moved into its open position. When this occurs, the diode 56 is electrically connected in series with each of the signal lamps of the indicators in each of the traffic signal faces 16-22 thereby abruptly dimming traffic signal lamps connected to the rectier. By using a rectifier as the diode 56, the power applied to the lamp is decreased to about one-half of its original value and the light intensity drops from about a percent level to about a 26 percent level. The reduction in power and lamp intensity is due to diode 56 conducting only during onel9 half the portion of the alternating current voltage cycle.

The above represents one possible solution to the problem of dimming traffic signal lamps either in a single phase, a plurality of phases or of the entire intersection. The light responsive electrical lamp dimming system is disclosed and claimed in an application led concurrently herewith of Stanley L. Ross, identilied as Serial No. 742,628.

In certain applications, it is desirable not to abruptly dim the entire intersection but to proportionally dim only selected traic signal lamps or indications. By using the teachings of the present invention, at least four possible combinations are possible: (1) dimming a single tratlic signal lamp or indication in a selected trafiic signal face; (2) dimming traffic signal lamps or indications which are identical and in the same phase wherein each lamp is located in a different traic signal face; (3) dimming traflic signal lamps or indications in a single trac signal face; and (4) dimming traic signal lamps or indications in a plurality of traic signal faces in the same phase. These typical combinations which utilize the teachings of the present invention will now be considered with respect to FIGURES 2 through 5.

FIGURE 2 discloses a single traic signal face 90 having a red indication 92, an amber indication 94, a green indication 96 and a left turn indication 98. Each of the indications 92-98 is selectively controlled from a traic signal controller (not shown) via control leads 100-106 respectively. Each of the neutrals of indications 92-98 is electrically connected to a-common neutral 110. The red indication 92 has a light responsive electrical lamp dimming circuit 112 electrically connected in series between it and its associated control lead 100. Similarly, other light responsive electrical lamp dimming circuits, which are illustrated as dashed line rectangles and designated as 112 in FIGURE 2, can be selectively connected between other indications 94-98 and the control leads 102-106 respectively. The circuit 112 is capable of proportionally dimming the intensity of the traliic signal lamp only of the red indication of the tratiic signal face 90 from a normal or high intensity level to a predetermined intensity level as a function of sensed background illumination. The traic signal lamps of the remaining indications (without circuits 112'), namely, amber ndication 94, green indication 96 and left turn indication 98, remain at normal intensity levels. Thus, a single control circuit 112 connected betWeen the control lead 100 and red indication 92 is capable of proportionally dimming a single trai'lc signal lamp or indication in a traffic signal face. A light responsive electrical lamp dimming circuit for dimming only a single traic signal lamp is illustrated in FIGURE 5.

Trailc signal lamps or indications which are identical and in the same phase but located in different traic signal faces can also be dimmed. For example, two control conductors 116 and 118 to other red indications located in other trac signal faces (not shown) can be proportionally dimmed by circuit 112. It is necessary that circuit 112 have a suicent current carrying capability to dim the desired number of traic signal lamps. A light responsive electrical lamp dimming circuit for dimming a plurality of traffic signal lamps, as described above, is illustrated in FIGURE 7.

FIGURE 3 illustrates a different traic signal face 120 which is similar to the traflic signal face 90 of FIGURE 2. However, traic signal face 120 includes a red indication 122, an amber indication 124, a green indication 126 and a right turn indication 128. Each of the tralc signal lamps of indications 122-128 is selectively controlled via control leads 132-138 respectively, which leads are in turn controlled by a traffic signal controller (not shown). The neutrals from each of the traffic signal lamps of indications 122-128 are electrically connected to a common neutral 140. Each of the tralc signal lamps of indications 122-128 is illustrated as being electrically connected to the control leads 132-138 respectively via series connected light responsive electrical lamp dimming circuits generally designated as 142-148 respectively, which control leads are in turn controlled by a traffic controller (not shown). By using a separate dimming circuit 142-148 for each indication in a traffic signal face, each trafc signal lamp is proportionally dimmed as a function of sensed background illumination. Thus, either some or all of the traific signal lamps or indications in a single traffic signal face can be proportionally dimmed. A dimming circuit which can be used as the dimming circuits 142-148 is illustrated in FIGURE 5.

FIGURE 4 illustrates a means for dimming all of the traffic signal lamps or indications in all of the tratic signal faces in the same phase. A traic signal face 156, which is typical of a plurality of trai-lic signal faces in the same phase, is illustrated in FIGURE 4 as having a red indication 158, an amber indication and a green indication 162. The trac signal lamps of indications 158-162 are controlled by control leads 164-168 respectively, which control leads are in turn controlled by a traffic controller (not shown). Each of the neutrals of the lamps of indications 158-162 is electrically connected to a single light responsive electrical lamp dimming means 170. Dimming means is in turn electrically connected to a common neutral 172 which in turn is connected to the system ground. If a phase utilizes more than one traic signal face, all of the traic signal faces in that phase must be electrically connected together and in lturn be connected to a single dimming means 170, having suicient current carrying capacity, which is in turn connected to the system ground. When a single control circuit 170 is required to control more than one face, a common neutral from each face, such as for example common neutrals illustrated as dashed lines 171 in FIGURE 4, is connected together before the control circuit 170. In this application, it is necessary that all the common neutrals from the faces on the same phase be connected together such that ground loop problems are eliminated and the desired dimming of the entire phase between a high intensity level and the predetermined low intensity level is obtained. A dimming means 170 for controlling a single phase having a single traic signal face is illustrated in FIGURE 7.

FIGURE 5 is a schematic diagram of a light responsive electrical lamp dimming circuit which could be used as the dimming circuit 112 and 112 of FIGURE 2 or as the dimming circuits 142-148 of FIGURE 3. For purposes of example, the dimming circuit illustrated schematically in FIGURE 5 is the dimming circuit 112 of FIGURE 2.

Dimming circuit 112 controls dimming of the traffic signal lamp 92 of the red indication 92. The lamp 92 is electrically connected to the control lead 100 which is selectively switched to a source of alternating current voltage 174 'by the tralc signal controller, which is represented by the single pole, single throw switch identified TSC. Thus, the dimming circuit 112 is essentially electrically connected in series between the lamp 92', whose intensity is to be proportionally dimmed, and the control lead 100. The neutral of lamp 92 is in turn connected to the common neutral 110.

The circuit which forms the dimming circuit 112 includes a capacitor 176 electrically connected between the control lead 100 and lamp 92', An inductor 178 is electrically connected in parallel to the capacitor 176. Capacitor 176 and inductor 178 function to suppress undesired radio frequency signals and the like generated within the circuit 112 from being applied across the voltage source 174. A photocell 182, which forms part of the background illumination sensing means, is connected to the inductor 178 via resistor 190 and is used to control the sensitivity of a bi-directional triggering means, generally designated as 184, which is used to control a bidirectional conducting means, generally designated as 186, which is essentially connected in series with lamp 92. The

triggering means 184 and the conducting means 186 may be an integral solid state device, generally designated as 188. The conducting means 186 selectively conducts an electrical current through the lamp 92', the magnitude of which depends on the state of conduction of the conducting means at the time it is rendered conductive. The photocell 182 is electrically connected to the lamp 92 by a capacitor 192. A variable resistor 1'94 is electrically connected in parallel to the photocell 182, and variable resistor 194 is used to adjust the sensitivity level for the triggering means 184. The predetermined low intensity to which lamp 92' is to be dimmed is selected by the value of resistance of resistor 194.

The remaining portion of the background illumination sensing means includes, in addition to the photocell 182, a light reducing means, generally designated as 198. In this embodiment, the light reducing means 198 is a red jewel 200 and an apertured disk 202. The red jewel 200 and apertured disk 202 selectively control the amount of ybackground radiation or light from the background illumination which impinges on the photocell 182. The resistance of the photocell 182 in turn varies the switching state or phase angle of conduction of conducting means 186, which in this embodiment is a bi-directional semiconductor device. In this way, the dimming circuit 112 proportionally dims the lamp 92' as a function of sensed background illumination.

Typically, the operation of the dimming circuit of FIG- URE 5 is as follows. The background illumination in the vicinity of the lamp 92 is sensed by the background illumination sensing means, which in this exemplary embodiment comprises a photocell 182 and a light reducing means 198. When the background illumination is at a bright level, the light reducing means 198 reduces the level of the illumination to about 2 footcandles or so causing the resistance of the photocell 182 to be at a Value which enables the triggering means, which is a triggering circuit formed of resistor 190, photocell 182, variable resistor 194, capacitor 192 and triggering diode 184, to permit the bi-directional thyristor 186 to conduct at a rst state or at a first phase angle of conduction. This permits an electrical current to pass through the lamp 92' to establish a voltage thereacross for substantially an entire portion of the alternating current cycle which operates the lamp at a high intensity level.

As the background illumination varies from and becomes less than the bright level, the radiation impinging upon the photocell 182 via the jewel 200 and apertured disk 202 also proportionally reduces in intensity. The reduced amount of radiation impinging on the photocell 182 causes the resistance thereof to increase proportionally to the decrease in background illumination level. The increase in resistance of the photocell 182 causes the triggering means or the triggering circuit to vary the state or angle of conduction of the conducting means 186 in proportion to the decrease in background illumination.

When the background illumination reaches a predetermined low intensity level, the intensity of the illumination reaching the photocell is substantially at zero foot-candles and the resistance of the photocell 182 remains at substantially a high value. The resistance of the photocell 182 together with the resistance of resistor 194 establishes the minimum triggering condition of the conducting means 186. In particular, a second state or second angle of conduction is established wherein an electrical current is passed through the lamp -to establish a voltage thereacross for at least a portion of the alternating current voltage cycle which operates the lamp at the predetermined low intensity level. Thus, the conduction of the conducting means 186 is varied between the rst state, or first angle of conduction, and the second state, or second angle of conduction, in proportion to sensed changes in background illumination which varies from a bright level to a preselected dark level. When the background illumination is at or below the preset dark level, the

intensity of the lamp is maintained at the predetermined low intensity level.

Typical components for the circuit of FIGURE 5 are listed hereinbelow.

Signal lamp 92-150 watt tungsten lamp. Capacitors 176, 192-.O47 nf., 400 volts. Inductor 178-100 ith., torroidal coil, 30 turns of AWG wire on .68 O.D. x .35 I.D. x .27" thick torroidal core Photocell 182-GE. B245 Resistors:

190-4.7k$2, 1/2 watt 194-500 kQ potentiometer, 1/2 watt Triggering diode 184 and Bi-directional semiconductor device 186 (An integral unit 188)-Quadrac; Electronic Control Corporation Cat. No. Q2005T The curve of FIGURE 6 illustrates the characteristics of the dimming circuit of FIGURE 5 using both a red jewel and a yellow jewel as the jewel 200 together with the aperture disk 202 having an aperture in the order of about 1/16 inch (about 2 mm.) to about l/s inch (about 3.5 mm.). In FIGURE 6, three curves are illustrated, curve 206 for the circuit using a red jewel which represents the voltage across the lamp as a function of illumination in foot-candles, curve 208 for the circuit using a yellow jewel which represents the voltage across the lamp as a function of background illumination in foot-candles, and curve 210 for the circuit using a yellow jewel which represents the percent light output of the lamp plotted as a function of background illumination in foot-candles. From curve 210, it is readily apparent that the dimming of the signal lamp is substantially proportional to the background illumination and the percent of light output of the lamp can be selectively controlled betweenabout l5 percent, at a very low background illumination, to slightly more than about 95 percent for a relatively bright background illumination. When the background illumination is in excess of 1200 foot-candles, the percentage light output of the lamp approaches percent.

FIGURE 7 illustrates schematically an embodiment of a circuit for a light responsive electrical lamp dimming circuit 170 of FIGURE 4 for controlling a phase having only a single traffic face. For purposes of explanation, operation of only the tratiic signal lamp 158' of red indication 158 is illustrated. It is understood that the traic signal lamp for the amber indication 160 and green indication 162 are electrically connected in parallel to the lamp 158 and would be simultaneously dimmed.

The lamp 158 is electrically connected to the control lead 164 which is selectively switched to an alternating current voltage source 222 by the traflic signal controller, which is represented by the single pole, single throw switch identified TSC.

The dimming circuit generally includes a radio frequency filtering network connected across the lamp 158 and to common neutral 172 which is formed of a resistor 223 connected in series with a capacitor 224 and in parallel to a second capacitor 226. In addition, the filtering network includes an inductor 228 which is electrically connected in series with the common neutral 172.

A trimming or extended range circuit, which enables the circuit to operate over a wider range of maximum and minimum limits, is connected across the lamp and to common neutral 172. The extended range circuit includes a resistor 232 having one end thereof connected to the neutral of lamp 158 and with the other end of which is connected at a common junction terminal witha capacitor 234 which in turn is connected to a common conductor 230. Common conductor 230 is connected via inductor 228 to common neutral 172. The remainder of the extended range circuit includes a second resistor 244 having one end thereof connected to the neutral of lamp 158 and with the other end thereof connected at a common junction terminal with a capacitor 242 and a resistor 1-3 ductor 230. The resistor 236 is also connected to the com- 236. Capacitor 242 in turn is connected to common conmon junction terminal of resistor 232 and capacitor 234.

The triggering means or triggering portion of the sensing circuitry includes a photocell 240 `which forms part of the background illumination sensing means. The photocell 240 is electrically connected in parallel to resistor 244. Resistor 244 also serves the function of establishing the predetermined low intensity level of the lamp 158. A bi-directional triggering diode 246 is electrically connected to the common junction terminal between photocell 240, capacitor 242 and resistor 244 and is responsive to the charge built up on capacitor 242 to trigger a bidirectional conducting device 248, which may be for example a triac.

The background illumination sensing means further includes, in addition to the photocell 240, a light reducing means, generally designated as 250, which selectively and proportionally controls the amount of background radiation or intensity representing the background illumination which reaches the photocell 240. In this embodiment, the light reducing means 250 includes a jewel, generally designated 252, and an apertured disk 254. The combination of the jewel 252 and apertured disk 254 controls the amount of radiation of the background illumination which is directed upon and impinges upon photocell 240. The radiation directed upon the photocell 240 varies as a function of the changes in background illumination in the vicinity of the traffic signal face 156 and in turn varies the resistance of the photocell to provide a substantially linear dimming of the lamp 158 in proportion to sensed changes in background illumination.

The operation of the dimming circuit of FIGURE 7 is very similar to the dimming circuit of FIGURE 5. Thus, a detailed description of circuit operation as a function of sensed changes in background illumination is not deemed necessary. l It is important that the operational characteristics of the background illumination sensing means be selected or matched, so to speak, with the lumen level of the background illumination.

As discussed hereinbefore, a photocell abruptly changes its resistance from a low resistance to a high resistance in response to about 2 foot-candles to about zero footmeans must be capable of providing a change in operational characteristics as a function of and substantially in proportion to the change in background illumination. The change in operational characteristics disclosed herein is a change of resistance of a photocell. The amount of light -which impinges on the photocell is selectively reduced, or filtered in these embodiments, by a light reducing means. A change in light energy `which impinges onto the photocell causes a change in resistance thereof which is proportional to the changes in background illumination. In the absence of such a light reducing means, it was determined that a photocell, not so selected or compensated, operated substantially as a bi-directional switch.

Typical components capable of being used in the embodiment of FIGURE 7 are set forth hereinbelow.

Lamp 158-G.E. Model #12S-1, 150 wana-120 v. A.C. Resistor 22S- 8252 Capacitor:

224-,22pf., 400 Volts 226.047ptf., 200 volts Inductor 22S-100Mb., torroidal coil, 30 turns of AWG wire on .68 O.D. x .35 LD. x .27" thick torroidal COle Resistor 232-68kt) Capacitor 234-.1,uf., 400 volts Resistor:

244-82kt) (could vary depending on photocell from k@ to 100km Capacitor 242-laf Photocell 240-GE. B425 Bi-directional triggering diode 246-G.E. ST2 Triac 248-G.E. SC41B Table I hereinbelow discloses the operation characteristics of the circuit of FIGURE 7. In Table I, background illumination is shown in foot-candles in both a westerly and an easterly direction and the lamp precent illumination viewing in an easterly direction and voltage applied across the lamp is shown wherein the light reducing means is a red jewel with an apertured disk having about a 1/16 inch (approximately 2 mm.) aperture. Clearly, the dimming of the lamp is proportional to the decrease in backcandles of lllumlnatlon respectively. By means of the llght 4 ground lllumlnatlon.

TABLE I (Around sunset) background (East viewing) light illumination Time reducing means (foot-candles) between (volts) red jewel readings Lamp percent, with aperature disk West East Remarks (min.) illumination H6 (2 mm.)

500+ 0 100 123 500+ 7 88 118 500 do 15 82 115 500+ 350 Sun behind cloud. 21 82 1 15 500+ 240 do 17 75 112 500+ 10 71 110 220 12 55 103 160 10 49 100 45 9 36 94 19 6 31 90 6 10 27 88 2 8 27 88 0 7 27 88 Euns=125 volts; Erine-EpnomiFlZS volts; Photocell: G.E. B425.

(Open circuit) (Photocell in circuit) vary over a wide range of illumination levels, such as for example from about 1200 foot-candles to zero footcandles, and the intensity of the controlled lamp can be varied by the photocell in proportion to the change in background illumination.

Table II hereinbelow discloses the operating characteristics of the circuit of FIGURE 7 showing the lamp percentage illumination for a different light reducing means; namely, a blue jewel with a red filter instead of an apertured disk. In Table II, background illumination is shown in foot-candles in a westerly, easterly and overhead direction and shows the lamp percentage illumination viewing in both an easterly and westerly viewing direction.

In summary, the background illumination sensing In this Table II, it is readily apparent that the dimming of the controlled lamp is proportional to the sensed changes in background intensity.

16 ming system can be easily installed into existing traffic signal control systems.

TABLE II Light reducing means blue jewel Background illumination Time with red i'llter (foot-candles) between Lamp (volts) readings percent, West East Overhead Remarks (min.) illumination East West 1,225 400 1, 175 Behind Cloud 0 99. 4 122 122 6, 400 650 1,800 Sum up ...Y 15 99. 4 123 123 1, 600 240 400 do 70 92. 4 120 124 400 140 240 Sun up tree. 20 81. 9 116 120 180 65 150 Sun half dow 10 74. 6 112 119 10 60. 8 106 115 10 43. 1 95 106 10 35. 8 92 100 7 30. 5 90 96 5 25. 5 87 91 5 25.0 87 88 8 23.5 86 S6 5 23. 5 86 86 23. 5 86 86 (Open circuit) (Photocell in circu FIGURE 8 is a graph showing a curve 266 which represents the percent light output as a function of voltage across the lamp in FIGURE 7 when a yellow jewel is used for the jewel 252.

FIGURE 9 is a fragmentary cross-sectional elevational side view of an assembled and packaged circuit of FIG- URE 5 installed in a traic signal section. The assembled and packaged circuit is generally illustrated as 272. The rearwardly located and lower exterior walls of a traflic signal housing are represented by cross-sectional housing 274. The rearwardly located exterior wall is drilled and tapped to form a threaded aperture 276 which is adapted to receive a threaded yellow plug member 278. The yellow plug member 278 may be a S. S. White special plastic protector part #160480-Y described in their catalog dated August 1965 having a diameter of 5/8 inch (about 1.6 cm.) and a pitch of 18 threads per inch (about 18 threads per 2.54 cm.). The yellow plug member 278 has an outer flange 280 which is spaced from the rearwardly located exterior wall of housing 274 by means of a waterproof gasket 282. The overall dimension of flange 280 is approximately 7A; inch (about 2.25 cm.). The top portion of the threaded yellow plug member 278 has a slot 286 which is adapted to receive the bit of a screwdriver for threading the yellow plug member 278 into threaded aperture 276. The slot 286 also forms a thin outer Wall section of the plug 278 which enables the portion of the plug just below the slot to form a lter for background illumination. The center of the plug member 278 is hollowed-out so as to form a light passage area 290. An apertured disk 292 is located within the hollowed-out area or light passage area 290 and adjacent the portion of the yellow plug member 278 just below slot 286.

Thus, background illumination in the vicinity of the traffic signal section passes through the slot 286 of the plug member 278 and is generally focused to a small beam having a predetermined cross-sectional area by means of the apertured disk 292 (having a diameter in the order of a few mils). The light beam then passes through the hollowed-out area 290 and impinges upon an aligned photocell which is located in the packaged circuit 272. In this manner, the amount of background illumination impinging on the photocell within the packaged circuit 272 selectively changes the resistance of the photocell such that proportional control and dimming can be obtained. In this embodiment, if the plug member 278 and the apertured disk 292 were omitted, the photocell would merely abruptly change its resistance when the background illumination reached a certain level. When this occurs, the device is then operative as a bi-stable switching device.

By using these teachings, a relatively inexpensive, effective and waterprQOf light responsive electrical lamp dim- FIGURE 10 is a fragmentary cross-sectional elevational side view of an assembled and packaged circuit of FIGURE 7 installed in a traiic signal section similar to that of FIGURE 9. The assembled and packaged circuit is generally illustrated as 300. The rearwardly located and lower exterior walls of a tratiic signal section are i1- lustrated in cross-section with the rearwardly located exterior wall designated as 302. Exterior wall 302 has a threaded aperture 306 which is adapted to receive a threaded nipple 308 such that the end of the nipple 308 protrudes or extends slightly beyond the outer surface of exterior wall 302. A red jewel member 310 has a threaded adjustable collar 312 which is adapted to be threaded onto the extended or'protruding portion of the nipple 308 such that the red jewel member 310 is supported in the alignment with the end of the nipple 308. Also located at the end of the nipple 308 and in alignment with the red jewel member 310 is an apertured disk 314. Disk 314 receives the radiation from the background illumination from red jewel member 310 and functions to limit the radiation from the background illumination to a predetermined cross-sectional area. The interior or center of nipple 308 permits the limited amount of background illumination passing through apertured disk 314 to impinge on the photocell (240 of FIGURE 7) which is located in the packaged circuit 300 adjacent the other end of nipple 308.

In this embodiment, the red jewel member 310 and the apertured disk 314, in combination, selectively permit a limited amount of background illumination to impinge upon and vary the resistance of the photocell as a function of the change in background illumination. The change in resistance of the photocell enables circuit 300 to variably dim the traiiic signal lamp in proportion to the sensed change in background illumination. The packaged circuit 300 as described herein together with the nipple 308, red jewel member 310, collar 312 and apertured disk 314 can be easily installed into an existing traiiic signal section.

It is readily apparent from the embodiments described herein that many other combinations, modications, improvements and the like can be made of the light responsive electrical lamp dimming system, circuits and means disclosed herein and all are deemed to be within the scope of the appended claims.

What is claimed is:

1. A light responsive electrical lamp dimming means comprising a pair of leads one of which is adapted to be electrically connected in series with a lamp to be dimmed;

a controllable bi-directional conducting means capable of being selectively rendered conductive electrically connected in series with said leads;

triggering means electrically connected in parallel with and operatively connected to said bi-directional conducting means which, when an alternating current voltage is applied across said series connected lamp and said bi-directional conducting means, selectively varies the state of conduction of said bi-directional conducting means between a first state wherein an electrical current is passed through said lamp to establish a voltage thereacross for substantially an entire portion of the alternating current cycle which is capable of operating said lamp at a high intensity level and a second state wherein an electrical current is passed through said lamp to establish a voltage thereacross for at least a portion of the alternating current voltage cycle which is capable of operating said lamp at a predetermined low intensity level; and

background illumination sensing means adapted to detect changes in background illumination in the vicinity of said lamp and operatively connected to and capable of controlling said triggering means for varying conduction of said bi-directional conducting means between said first state and said second state in proportion to sensed changes in background illumination.

2. The electrical lamp dimming means of claim 1 further comprising means operatively coupled to said triggering means for disabling control thereof in response to said background illumination sensing means when said background illumination decreases below a preselected dark level and for establishing conduction of said bidirectional conducting means at said second state whereupon said lamp remains at said predetermined low intensity level whenever said background illumination is at a level below said preselected dark level.

3. The electrical lamp dimming means of claim 2 wherein said background illumination sensing means includes a light reducing means disposed to receive and selectively transmit light from said background illumination as a light beam having an intensity which varies in proportion to the changes in said background illumination; and

a light sensing means capable of varying its resistance as a function of light incident thereon operatively coupled to said triggering means and positioned adjacent to and in alignment with said light reducing means to receivesaid light `beam for controlling operation of said triggering means in response to said sensed changes in said background illumination.

4. A light responsive electrical lamp dimming system adapted to be connected in series with a lamp which is energized from a source of alternating current voltage for proportionally controlling intensity of said lamp between a high intensity level and a predetermined low intensity level as a function of background illumination in the vicinity of said lamp, said system comprising a controllable bi-directional semiconductor device adapted to be electrically connected in series with a lamp for controlling conduction of an electrical current through said lamp when bi-directional semiconductor device is rendered conductive;

triggering means operatively connected to said bi-directional semiconductor device for selectively varying conduction thereof between a first state wherein an electrical current is passed through said lamp to establish a voltage thereacross for substantially an entire portion of the alternating current cycle which operates said lamp at said high intensity level and a second state wherein an electrical current is passed through said lamp to establish a voltage thereacross for at least a portion of the alternating current voltage cycle which operates said lamp at said predetermined low intensity level;

means operatively coupled to said triggering means for disabling control thereof when said lamp reaches said predetermined low intensity level for setting the conduction state of said bi-directional semiconductor device at said second state whereupon said lamp remains at said predetermined low intensity level whenever said triggering means attempts to change conduction of said bi-directional semiconductor device to a state which is other than between said first and second states; and

background illumination sensing means adapted to detect changes in background illumination in the lvicinity of said lamp, said background illumination sensing means comprising means for selectively transmitting light from said background illumination along a predetermined path, and

light responsive means operatively coupled to said triggering means and positioned along said path and adapted for receiving light from said background illumination to control said triggering means for varying conduction of said ybi-directional semiconductor device between said first state and said second state in proportion to sensed changes in background illumination.

5. The electrical lamp dimming system of claim 4 wherein said selectively transmitting means includes a filter disposed to receive and selectively transmit,

along said predetermined path, light from said background illumination as a light beam Vwhich varies in intensity in proportion to changes in said background illumination; and an apertured disk positioned along said predetermined path between said filter and said light responsive means for reducing said light beam to a predetermined cross-sectional area. V6. A light responsive electrical lamp dimming apparatus comprising an electrical circuit comprising -a pair of leads one of which is adapted to be electrically connected in series with a lamp to be dimmed,

a bi-directional gate controlled switch electrically connected in series with said leads and said lamp, said gate controlled switch being capable of Ibeing selectively rendered conductive when an alternating current voltage is applied across said series connected lamp, leads and gate controlled switch, and

a triggering circuit operatively connected in parallel to said gate controlled switch and operatively connected to the gate of said gate controlled switch, said triggering circuit includmg a bi-directional triggering diode having one of its leads electrically connected to the gate of said gate controlled switch,

a photocell electrically connected Ibetween the other lead of said bi-directional triggering diode and said one lead connected in series with said lamp,

a capacitor electrically connected between said other lead of said bi-directional triggering diode and the other of said pair of leads, and

resistance means electrically connected to said photocell and the other lead of said bidirectional triggering diode for.establishing a lminimum angle of conduction at which said bidirectional triggering diode can render said bi-directional gate lcontrolled switch conductive; and

light reducing means positioned adjacent said photocell and adapted to selectively transmit light of an intensity level which varies the resistance of said photocell in proportion to change in intensity level 19 of background illumination in the vicinity of said lamp. 7. A light responsive electrical lamp dimming means adapted for use with a traffic signal control system energized from an alternating current voltage source wherein said dimming means proportionally controls intensity of a traflic signal lamp between a high intensity level and a predetermined low intensity level as a function of background illumination in the vicinity of the trafiic signal lamp, said dimming means comprising a controllable bi-directional conducting means adapted to be electrically connected in series with said lamp for selectively controlling conduction of an electrical current through said lamp as a function of the phase angle and voltage amplitude of the alternating current voltage when Isaid conducting means is rendered conductive; triggering means operatively connected to said controllable bi-directional conducting means for selectively varying the angle of conduction thereof between a first angle of conduction wherein an electrical current is passed through said lamp to establish a voltage thereacross for substantially an entire portion of an alternating current cycle which operates said lamp at a high intensity level and a second angle of conduction wherein an electrical current is passed through said lamp to establish a voltage thereacross for at least a portion of an alternating current cycle which operates said lamp at a predetermined low intensity level; and background illumination sensing means capable of detecting background illumination in the vicinity of said lamp for controlling said triggering means to vary the angle of conduction of said controllable bidirectional conducting means between said first conduction angle and said second conduction angle in proportion to changes in sensed background illumination.

8. The electrical lamp dimming means of claim 7 further comprising means operatively coupled to said triggering means for disabling control thereof by said background illumination Isensing means when said background illumination decreases below a preselected dark level when said triggering means has established conduction of said controllable bi-directional conducting means at said second angle which operates said lamp at said predetermined low intensity level whenever said background illumination level is below said preselected dark level.

`9. The electrical lamp dimming means of claim 8 wherein said background illumination sensing means includes a light reducing means disposed in a traffic signal face of said traffic control system and positioned to receive and selectively transmit light from said background illumination directly behind 'said traffic signal face as a light beam having an intensity which varies in proportion to the changes in said background illumination; and

.a light sensing means capable of varying its resistance as a function of incident light thereon operatively coupled to said triggering means and positioned adjacent to and in alignment with said light reducing means to receive said light beam for controlling operation of said triggering means in response to t 'changes in said background illumination.

10. The electrical lamp dimming means of claim 7 wherein said dimming means is electrically connected between a control lead and a single trafiic signal lamp of a traiiic signal face.

11. The electrial lgmp dimming means of claim 10 adapted for use it; an intersctipn having at least a one phase tra entrollcr wherein said dimming means iS 20 electrically connected between all of the traffic signal lamps of the same indication located in different traffic signal faces in the same phase.

12. The electrical lamp dimming means of claim 10 wherein a separate said dimming means is electrically connected between more than one traffic signal lamp and its associated control lead in the same traffic signal face.

13. The electrical lamp dimming means of claim 10 adapted for use in an intersection having at least a one phase traiiic controller wherein said dimming means is electrically connected between the common neutrals of all traffic signal faces of the same phase.

14. The electrical lamp dimming means of claim 7 wherein said source of alternating current is capable of being a voltage of approximately 120 volts, 60 HZ. and wherein the intensity of said traffic signal lamp can be varied from between about percent intensity level and about 23 percent intensity level.

15. The electrical lamp dimming means of claim 9 wherein said light reducing means includes a filter disposed to receive and selectively transmit along a predetermined path said light from said background illumination as said light beam which varies in intensity in proportion to changes in said background illumination; and

an apertured disk positioned along said predetermined path between lsaid lter and said light sensing means for reducing said light beam to a predetermined cross-sectional area.

16. rlhe electrical lamp dimming means of claim 15 wherein said controllable bi-directional conducting means is a bi-directional gate controlled switch and wherein said triggering means further comprises a bi-directional triggering diode having one of its leads electrically connected to the gate of said gate controlled switch and its other lead electrically connected to said light sensing means;

a capacitor electrically connected between the other leads of said bi-directional triggering diode and the output of said gate controlled switch; and

resistance means electrically connected to said light sensing means and to the other lead of said bi-directional triggering diode for establishing said second angle of conduction at which said bi-directional triggering diode can render said bi-directional gate controlled switch conductive.

17. The electrical lamp dimming means of claim 11 further comprising a radio frequency suppressing circuit electrically connected across said bi-directional gate controlled switch.

18. The electrical lamp dimming means of claim 16 wherein said bi-directional gate controlled switch is a triac and wherein said light sensing means is a photocell.

19. The electrical lamp dimming means of claim 18 wherein said resistance means is a resistor electrically connected in parallel with said photocell.

20. The electrical lamp dimming means of claim 18 wherein said filter is selected to be a yellow jewel and said apertured disk has an aperture of about 1/16 inch.

21. The electrical lamp dimming means of claim 18 wherein said filter is selected to be a red jewel and said apertured disk has an aperture of about 1A@ inch.

22. The electrical lamp dimming means of claim 21 further comprising a radio frequency suppressing circuit electrically connected between said lamp and said triac; and an extended range circuit electrically connected between said radio frequency suppressing circuit and said triac. v

(References on following page) References Cited UNITED STATES PATENTS JOHN W. HUCKERT, Primary Examiner SIMON BRODER, Assistant Examiner Seidler 315-159 Patterson 315-292 U-SC1XR Feser et al. 340-40 5 315-154, 194; 340-40, 335 Pfennighausen et al. 340-22 Jahns et al. 315-149

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