US3040168A - Instrument lighting device - Google Patents

Description

June 19, 1962 T. STEARNS 3,040,158

INSTRUMENT LIGHTING DEVICE Filed Sept. 25, 1957 4 Sheets-Sheet 1 INVENTOR. ZWoIe A ra/y 5215mm BY W June 19, 1962 'r. STEARNS 3,040,163

INSTRUMENT LIGHTING DEVICE Filed Sept. 25, 1957 4 Sheets-Sheet 2 INVENT OR. 7770/9/10 JA STE/7616 BYW a June 19, 1962 T. STEARNS INSTRUMENT LIGHTING DEVICE 4 Sheets-Sheet 5 Filed Sept 25, 1957 June 19, 1962 T. ,STEARNS INSTRUMENT LIGHTING DEVICE Filed Sept. 25, 1957 4 Sheets-Sheet 4 15.24. R25- m //4 m //6 INVENTOR. fla /v72 5259mm arraa/m Unite'dsiats Patent My invention relates to a non-glare illuminatin means for illuminating displays such as aircraft instrume ts, and more specifically relates to a non-glare illuminatin means of the so-called wedge type which gives a uniformly distributed illumination of a display. i

Wedge lighting for devices such as aircraft instruments is well known in the art and com-prises the use of a transparent wedge-shaped body which is positioned in front of a display such as an aircraft instrument dial and in a plane substantially parallel to the plane of the dial. A

light rays after they are within the wedge, or to control or extend the angular distribution of the light rays by light source is placed at the wide base of the wedge and light rays are directed from the wide base towards the apex of the wedge.

More specifically, light rays entering the wedge base and impinging on the sides at angles greater than the critical angle of total reflection will receive multiple total reflections from the inner surfaces of the wedge. With each successive reflection, the rays will approach the next surface at a lesser angle until they impinge upon a surface at an angle which is less than the critical angle for,

surface. Clearly, the light which emerges from the side djacent the dial surface or display surface will serve to illuminate the display, while the light emerging from the opposite side of the surface will emerge as glare.

in order to eliminate at least a portion of this glare it is possible to place a second wedge adjacent the first wedge with its apex adjacent the base of the first wedge. When the wedges are in this relation the light which normally emerges as glare will now be impinged upon the second wedge and, because of refraction, will impinge the wedge material whereupon they will emerge from that upon the opposite surface of the second wedge at an angle which is greater than the critical angle. The rays will then undergo multiple internal reflections at successively greater angles going down the secondwedge and towa-d its base where it may be trapped in a light trap,

or may be utilized to illuminate a second display.

One of the major difficulties with the above noted type of wedge lighting system is that the dial surface is not uniformly lighted, but the lighting is more intense at the lower dial portions adjacent the apex side of the first wedge.

The primary reason for this non-uniformity is that an insufficiently wide range of light rays enters the wedge at its upper and wide portions and thus few or no rays impinge uponthe inner surfaces near the base at an angle which is less than the critical angle to emerge and thereby impinge upon the display to be illuminated.

Therefore, the upper portion of the dial or display is not illuminated to the same intensity as are the lower portions which are illuminated by rays which enter the base of the wedge at an angle which is greater than the critical angle and approach the critical angle after a plurality of reflections within the wedge so as to thereafter emerge from the wedge to illuminate the lower por tions. That is to say, light does not escape from the region close to the base of the wedge because the angular range of the rays entering is normally insuflicient to include rays which emerge before undergoing several internal reflections.

The principle of my invention is to control or extend the angular range of the rays entering the base of the wedge or to control or extend the angular range of the combinations of both of these means, thus to secure more efficient and uniform illumination of the display.

In one embodiment of my invention the base portion of the wedge could be'corrugatcd to thereby assure that substantially all. light rays impinged upon the wedge base will be distributed internally so as to emerge equally throughout the length of the wedge.'

In another embodiment of my invention it may be sufiicient to roughen the surface of the base whereby each roughened particle will serve as a secondary source sending out rays in all directions within the material of the wedge.

In each of the two embodiments above described a small portion of the wedge surface may be coated with a reflecting material which will operate as a secondary source within the wedge material. Thus, the light rays which enter through the corrugated portions of the wedge or the roughened surface of the wedge will have at least a portion thereof impinged upon the reflecting material which will operate as a secondary source primarily for illuminating the. upper portion of the display.

- In the circular shaped display, I have further found that the uniformity of lighting over the dial surfaces is increased by making one surface of the first wedge concave and the adjacent surface of the second wedge convex. This increases the angle between the wedge surface closest to the light source thus requiring fewer successive internal reflections to achieve incidence angles less than critical in this region of the wedge. This increases the illumination adjacent to the lamps. In addition, this always has the effect of making the center section of the wedge thinner than the edge in a region extending above the light sources toward the thickest point of the edge so that the wedge distributes some light above the light sources in the normal manner.

It has been further found that the surface at which light enters the round wedge devices may be concave rather than grooved while still achieving the desired uniform lighting. The concave shape, however, is easily polished and this feature aids in concealing the light source from an observer viewing the display.

It is to be noted that this problem has been dealt with in the past by forming the wedge to have an obtuse angle between the base and the surface adjacent the display. This construction allows the upper display areas to be illuminated, since it allows rays to enter the upper portions of the dial at the critical angle. However, in this constructiomthe angular range of light rays which can be supplied by the light source is limited by theoretical Accordingly, the primary object of my invention is to provide a novel non-glare illuminating means for illuminating displays.

Another object of my invention is to provide a novel illuminating means for uniformly illuminating displays.

Another object of my invention is to provide a wedge type lighting illuminating means which achieves uniform illumination over the substantial length of wedge.

Another object of my invention is to provide a wedge type illuminating means wherein the heavy base portion of the wedge is adapted with secondary reflecting surfaces for achieving a uniformity in the illumination of the upper as well as the lower portions of the wedge.

A still further object of my invention is to provide a double wedge illumination system which uniformly illuminates a display and substantially decreases glare.

A further object of my invention is to provide a double wedge illuminating system for both rectangular and circular displays.

Another object of my invention is to provide a secondary emitting surface on the heavy portion of a wedge for illuminating a circular display wherein the light sources are positioned below the said heaviest portion of the wedge.

Another object of my invention is to provide a double wedge lighting system wherein the first wedge has a convex surface and the second wedge surface adjacent said FIGURE 16 shows a side view of a previously used type of wedge.

FIGURE 17 shows a side view of FIGURE 16 and schematically illustrates the manner in which illumination is distributed across the surface of a dial associated with the wedge.

FIGURE 18 is similar to FIGURE 11 and illustrates the convex surface of the wedge constructed in accordance with my invention.

FIGURE 19 is a side view of FIGURE 18 and illustrates the manner in which the convex surface more uniformly distributes the lighting of the dial associated with the wedge of FIGURE 18.

Referring now to FIGURES 1, 2a, 2b, 2c and 2d, it is desired to illuminate a first and second display 20 and 22 respectively wherein display 20 comprises a first, second and third longitudinal display associated with pointers 24, 26 and 28 respectively, while display 22 is a drum type display which is rotatable around an axis therethrough.

Instruments of these types are well known in the art and will not be described more fully hereinafter.

first surface is concave to further improve uniformity of lighting a circular display.

These and other objects will become apparent from the following description when taken in conjunction with the drawings, in which:

FIGURE 1 is a perspective view of a first and second wedge constructed in accordance'with my invention when positioned in front of a rectangular display.

FIGURES 2a, 2b, 2c and 2d are each side views of the device of-FIGURE 1 and schematically illustrate light rays proceeding down the length of the wedges to be irrpinged upon a display.-

FIGURE 3 shows the Wedge of FIGURES l and L. which have corrugated surfaces as being further provided with secondary reflecting surfaces for achieving a more uniform distribution of lighting for the display of FIG- URE 1.

FIGURE 4 is a side view of FIGURE 3.

FIGURE 5 is a perspective view of a circular display having illuminating means positioned in the corners of a square which would contain the circular display.

FIGURE 6 shows a front view of the second wedge of FIGURE 5.

FIGURE 7 shows a view of FIGURE 6 when taken across the lines 77.

FIGURE 8 is a front view of the first wedge adjacent to the dial surface in FIGURE 5.

FIGURE 9 is a top view of FIGURE. 8.

FIGURE 90 shows a view of FIGURE 8 when seen in the direction of the arrows 911-90.

FIGURE 10 is a side view of FIGURE 8.

FIGURE 11 is a cross-sectional view of FIGURE 8 when taken across the lines 11-11 and specifically shows the possible curvature which could be imparted to the surface of the wedge of FIGURE 8.

FIGURE 12 is similar to FIGURE 11 and specifically illustrates the operation of theacute angle formed between the dial surface and the wedge base in conjunction with the reflecting material fastened to the top surface of the wedge.

FIGURE 13 is a side view of FIGURE 12 specifically illustrating the manner in which the reflecting surface is applied to the base of the wedge.

FIGURE 14 shows another manner in which the wedge of FIGURES 8 and 12 could be constructed in conjunc- ItJion with a reflecting material impressed upon the wedge ase.

FIGURE 15 is a side view of FIGURE 14.

Positioned in front of these displays are a first and second wedge 30 and 32 respectively having their apices adjacent the base of the opposite wedge. In accordance with my novel invention, the base of the first wedge 30 which is adjacent to the dial 20 which is to be illuminated is corrugated, as seen by the slots 34, 36 and 38 running across the top of the base.

Positioned above this corrugated base, as best seen in this reflecting strip being a strip of white paint, a eoat-- ing of white ceramic, or any other material which would be a good reflector and is in intimate contact with the glass surface of the prism.

In operation, the light of the light sources 40 through 46 will enter the first wedge 30 and that portion of-the light which emerges from the dial side of the wedge will illuminate the dial.

The portion of the light which emerges from the opposite side of the first wedge, however, enters the upper portion of the outer wedge whereby some of this light is trapped by the blackened edges of the Outer wedge, as indicated in FIGURE 1 by a stippled area, while the remainder emerges from the dial side of the lower portion of the outer wedge to illuminate the cylindrical display 22. The remainder of the light will emerge from the front side of the outer wedge as stray light.

The operation of my novel wedge is more specifically set forth in FIGURES 2a, 2b, 2c and 2d wherein each of the figures trace the path of a first and second ray which are progressively further down the length of the wedge. Thus in FIGURE 2a, light rays from bulb 40 which enters the corrugated surface of the wedge is shown in solid lines 52 and 54. Light rays 52' and 54 enter the wedge and are totally reflected from the opposing surfaces of the wedge since they strike the surfaces at an angle which is greater than the critical angle.

After the first reflection light ray 54 achieves an angle which is less than the critical angle so that a ray 56 emerges from the wedge to impinge upon dia'. 20. The remainder, or refiectcd light of ray 54, seen as a short dotted line 58, emerges from the opposite side of the dial surface and enters the second wedge 32. A portion of the ray 58 which enters wedge 32 is internally reflected as is seen by the long dashed line 60, while the other portion of ray 58 emerges from the second wedge as stray light indicated by light ray 62.

Light ray 52 has a similar course to that of light ray 54 where the effective illuminating light of ray 52 emerges as ray '64 impinging upon dial surface 20.

Of the light which was reflected in the second we: go 32 and indicated by the long dashed line, it is seen that upon subsequent reflections this light approaches the sarface of the wedge at an angle which is increasingly greater than the critical angle required for emergence of light from the surface so that the light rays in the second wedge will execute multiple complete reflections until they reach the bottom of the wedge to emerge from the bottom of the wedge and illuminate the second display 22.

In order to increase the illumination of display 22, it is possible to provide an auxiliary reflecting surface 66 which receives emerging light that would normally not be impinged upon the display 22. Whatever light travelling down wedge 32 is not utilized in illuminating display 22 will be trapped in the blackened surface of the second wedge edges, as has been seen in FIGURE I.

FIGURE 2b shows a trace of rays which will be emitted from light source 40 which will be reflected a plurality of times until they achieve the critical angle required for emergence from the wedge surface to that rays 68 and 70 eventually emerge to illuminate a lower portion of the wedge, and in a similar manner, FIGURES 2c and 2d show the path of other light rays which will eventually emerge as rays 7274 and 76--78 respectively, which illuminate still lower portions of the dial surface.

It is to be noted that the solid lines in each of FIG- URES 2a through 2a represent the initial light ray emitted by the source, while the short dotted lines represent the path of remaining light after the light ray achieves its critical angle.

Thus, it is seen that by using my novel corrugated surface or roughened surface which causes a dispersion of the light as it enters the wedge, I can achieve a uniformity of illumination along the total length of the dial 20. In the past, as has been described above, it has been necessary to utilize a complex wedge construction of appreciable width at the base in order to have the rays of FIGURE 2a be useful rays which can operate to illuminate the upper portions of the dial surface.

If, in addition to the corrugated surface, the secondary source of FIGURE 3 were utilized so that light impinging upon strips 48 and 50 were reflected, then it is clear that a large portion of all the light which enters the wedge surface, regardless of its angle, will be utilized in illuminating dial 20 in a substantially uniform manner with the remainder illuminating display 22, with a very small portion of light being emitted as glare from lthe last surface of the second wedge.

It is important to note however that it is not essential to use corrugations if the secondary strips 48 and 50 are used. Furthermore, these strips 48 and 50 could be white ceramic coatings for diffusion of light impinged thereon, or reflecting coatings for actual reflection of light impinging thereon. If desired, one strip could be used and this strip could be the coated surface (not shown) of a separating member which separates two wedges when the double wedge is used.

FIGURES 1, 2a through 211, 3 and 4 have shown my novel invention in conjunction with a rectangular display. FIGURE 5 shows a perspective ,view of the manner in which my novel invention may be utilized in conjunction with a round display.

FIGURE 5 is more specifically comprised of a round dial 80 having a pivotally mounted pointer 82 rotatable with respect therewith. As was the case in FIGURE 1, illumination of dial 80 is achieved by means of a first and second wedge 84 and 86 respectively which have their apices adjacent the base of opposite wedges.

The second wedge 86 is seen in a side cross-sectional view in FIGURE 7, while FIGURE 6 shows a front view of wedge 86. FIGURE l, the outer surfaces of wedge 86 of FlGURE 5 are blackened in any desired manner so as to prevent the revelation of stray light, this blackening being schematically indicated by the stippled area.

As was the case of the second wedge of.

sources for illuminating display of FIGURE 5 are,

positioned in the corners of a square in which the round display 80 would fit so as to conserve space, these light sources being seen as bulbs 88 and 90.

Light sources 88 and are positioned adjacent portions 92 and 94 in the base of prism 84 whereby wedge action, as above described in FIGURES 2a through 2d,

will occur only for wedge portions below the level of light sources 88 and 90.

Thus, in a circular type of wedge, it is seen that the dial portions which are above the level of light sources 88 and 90 will not be illuminated.

That is, even though the portions 92 and 94 of the base of the first prism adjacent the display are constructed to be corrugated, the portions above the light sources still will not receive any substantial lighting.

In accordance with my invention, however, I have provided a secondary illuminating means, seen in FIGURES 9 and 10 as the reflecting surface 96 which receives light coming up the wedge, and diffuses this light b. ck and into the upper dial surface. This reflecting mellium could again be white paint or white ceramic material, as was the case of the secondary source material in FIGURES 3 and 4.

In order to further enhance the operation of this secondary source, the rear portion of the base may be sloped, as seen by the sloped surface 100 in FIGURE 10, the operation of which will be described more fully hereinafter.

While the base portions adjacent light sources 88 and 90 of FIGURE 5, or more specifically, portions 92 and 94 of FIGURES 8 and 9, could be of the corrugated nature as set forth above, I have found that I can also construct portions 92 and 94 to have concave polished surfaces such as the surface 102. of FIGURE 9a.

When the surfaces 92 and 94 are so constructed, 1 have found that I achieve the same desirable features of uniform lighting below the line of the light source while still obtaining a surface which is easily polished. so as to eliminate light spots at the edge of the illuminated display which are caused by irregularities in the surface through which light is emitted into the wedge.

The surface of the first wedge 84 which is away from the surface of display 80 may have a concave curvature, as seen at surface 104 of FIGURE 11 which cooperates with the convex shaped surface 89 of the second wedge 86 of FIGURE 7, thus achieving the results to be set forth hereinafter.

However. surface 104 could be a planar surface cooperating with a planar surface of the second wedge.

By whitening the upper base portion of. the wedge, as was set forth in FIGURES 8 and 9, I provide a secondary emitting surface which will reflect light coming up the wedge onto the dial 80. Thus, as may be seen in FIGURES l2 and [3, a layer of light reflecting material 96 is adhered to the surface of the prism. Hence. when light strikes the surface of reflecting material 96. it will be reflected to cause a first portion to go down the prism, as indicated by my 106, while a second ray 108 will be diffused into the upper portions of dial 80 of FIGURE 5 to thereby illuminate that upper portion of the dial which normally would not be illuminated because it is above the level of the light sources.

The distribution of light intensity at reflecting surface 9 6 is indicated by the length of the arrows within the circle 110 in FIGURE 12. Thus, by causing the surface to form an acute angle with respect to the wedge surface adjacent the dial, the intensity distribution curve is slanted circle 116.

over so that higher intensity rays are emitted towards the upper portion of the dial. If this relatively high in tensity illumination is not required at the upper portion of the dial, then the prism need not have the cut-away portion and may be shaped as set forth in FIGURES l4 and 15 where the upper base surface is coated with a reflecting material, as seen at positions 112 and 114.

Here again it is seen that light coming up the wedge will be impinged upon surface 112, and will be reflected with an intensity distribution given by'the lines within the Since the acute angle is not provided in the case of FIGURE 14, however, most of the light which is impinged upon the upper portions of the dial is re fiected from surface 114, rather than from surface 112-. In either'the structure of FIGURE l2 or FIGURE l4 an appreciable portion of the upper dial surface is illuminated. even though this portion is above the: light sources.

The effect of having the cooperating surfaces of the adjacent first and second wedges respectively concave and convex is best seen in FIGURES 16 through 19.

More specifically, FIGURES 16 and 17 show an inner wedge 118 which has a flat surface 3.20 which is adjacent a cooperating flat surface of a second wedge (not shown). if, in FIGURE 17, the light sources illuminating this wedge were point sources i292 and 3124, then the general light distribution across the wedge is seen in the curved lines indicating the discrete bands of illumination from these sources. Note that this effect of bands is eliminated by using sources of finite size in an actual case. The dash lines horizontally crossing the figure depict the sloping surface of the wedge in the same manner as contour lines show hills and valleys on a map.

By forming the wedge surfaces to be cooperating convex and concave surfaces as shown for prism 34 of FIGURE 18, then the distribution of light from point sources 122 and 124 is seen to be changed so that the light reaches more upward portions of wedge 84, as seen in FIGURE 19. Examination of the dashed contour lines shows why this is so since light from the edge is crossing contour lines even when travelling upward from the source, contrary to the condition for the planar wedge shown in FIGURES l6 and 17.

That is to say, portions of the dial surface 84) ot'FIG- URE adjacent the thicker portion of the wedge 84 of FIGURE 18, would be more illuminated than they would in the case of a pair of wedges having planar surfaces.

Thus, it is seen that the construction of my novel illuminating device of FIGURE 5 contains many features each of which could .be used individually or in any combination.

Although I have described preferred embodiments of my novel invention, many variations and modifications will now be obvious to those skilled in the art, and I prefer therefore to be limited not by the specific disclosure herein but only by the appended claims.

I claim:

l. A display illuminating device comprising a wedge of substantially transparent material positioned in front of said display and a light source positioned adjacent a relatively thick portion of said wedge for introducing light into said wedge; said wedge having arcircular face, said light source being positioned in the corner of a square within which said circular face wedge would fit whereby said light source does not appreciably extend the volume required for mounting said circular face wedge; a portion of the thicker portions of the base of said wedge other than the portion adjacent to said light source being coated with a reflecting material for reflecting illuminating light to the portions of said display adjacent the thicker portions of said wedge, said thicker portions of said wedge being further constructed to form an acute angle with respect to said display.

2. A display illuminating device comprising a wedge of substantially transparent material positioned in front of said display and a light source positioned adjacent a relatively thick portion of said wedge for introducing light into said wedge; said wedge having a circular face, said light source being positioned in the corner of a square within which said circular face wedge would fit whereby said light source does not appreciably extend the volume required for mounting said circular face wedge; a portion of the thicker portions of the base of said wedge other than the portion adjacent to said light source being provided with secondary light distributing means constructed to redistribute at least a portion of the light of said light source entering said wedge, said thicker portions of said wedge being further constructed to form an acute angle with respect to said display.

3. A display illuminating device comprising a wedge of substantially transparent material positioned in front of said display and a light source positioned adjacent a. relatively thick portion of said wedge for introducing light into said wedge; said wedge having a circular face, said light source being positioned in the corner of a square within which said circular face wedge would fit whereby said light source does not appreciably extend the volume required for mounting said circular face wedge; a portion of the thicker portions of the base of said wedge other than the portion adjacent to said light source being provided with secondary light distributing means constructed to redistribute at least a portion of the light of said light source entering said wedge; said portion of said wedge adjacent said light source having a polished concave surface, said thicker portions of said wedge being further constructed to form an acute angle with respect to said display.

4. A display illuminating device comprising a wedge of substantially transparent material positioned in front of said display and a light source positioned adjacent a relatively thick portion of said wedge for introducing light into said wedge; said wedge having a circular face, said light source being positioned in the corner of a square within which said circular face wedge would fit whereby said light source does not appreciably extend the volume required for mounting said circular face wedge; a portion of. the thicker portions of the base of said wedge other than the portion adjacent to said light source being provided with secondary light distributing means constructed to redistribute at least a portion of the light of said light source entering said wedge; said secondary light distributing means including a reflecting material on a portion of the face of said wedge adjacent said base which face is away from the surface of said display, said thicker portions of said wedge being further constructed to form an acute angle with respect to said display.

5. A display illuminating device comprising a first wedge of substantially transparent material positioned in front of said display and a light source positioned adjacent a relatively thick portion of said first wedge for introducing light into said first wedge; said first wedge having a circular face, said light source being positioned in the corner of a square within which said circular face first wedge would fit whereby said light source does not appreciably extend the volume required for mounting said circular face first wedge; a portion of the thicker portions of the base of said first wedge other than the portion adjacent to said light source being provided with secondary light distributing means constructed to redistribute at least a portion of the light of said light source entering said first wedge; and a second circular wedge; said second circular wedge having its heavy base portion adjacent the thin apex portion of said first circular wedge, said thicker portions of said first wedge being further constructed to form an acute angle with respect to said display.

(Other references on following page} 9 UNITED STATES PATENTS Rylsky Ian. 30, 1940" Triplctt Sept. 10, 1940 Christensen et a1. May 2, 1944 -Gardner Sept. 26, 1950 5 Prideaux et al. July 24, 1951 Levy May 26, 1953 1% Nierenbcrg et a1. July 28, 1953 Lazo Aug. 28, 1956 Hudson O91, 6,--1 959 FOREIGN PATENTS France Apr. 19, 1943 France Oct. 27, 1954

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