WO2016030217A1

WO2016030217A1 - Light-emitting diode lighting device comprising a light compatible with the use of night vision binoculars and comprising a light guide

Info

Publication number: WO2016030217A1
Application number: PCT/EP2015/068787
Authority: WO
Inventors: Arnaud Petitdemange; Sébastien Pelletier; Olivier Rols; Laurent Mozer
Original assignee: Thales
Priority date: 2014-08-29
Filing date: 2015-08-14
Publication date: 2016-03-03
Also published as: CA2959711A1; FR3025287B1; EP3186548A1; FR3025287A1

Abstract

The general field of the invention is that of lighting devices compatible with the use of night vision binoculars. Such a lighting device comprises at least: a row of first light-emitting diodes (11) carried and powered by an electronic circuit (12); a second light-emitting diode (14) surmounted by an optical filter (15), said optical filter having spectral transmission such that the light from the second diode filtered by said filter is compatible with the use of said night vision binoculars. The lighting device according to the invention comprises a light guide (16) comprising an input face (161) disposed in front of the second filtered light-emitting diode, a light guide area (162) of which the length is equal to that of the row of first light-emitting diodes and a plurality of diffusing output faces (163) disposed at and between the first light-emitting diodes.

Description

Light-emitting diode illumination device having compatible illumination of the use of night vision binoculars and comprising a light guide

The field of the invention is that of "NVG" compatible light-emitting diode devices for flat display screens such as liquid crystal matrices. By NVG-compatible lighting is meant lighting that can be used with NVG's "Night Vision Goggle" light-amplification binoculars, that is, the lighting does not saturate the binocular amplification systems. Lighting devices are also known in the Anglo-Saxon terminology of "backlighting". Flat screens have multiple applications. They can be used, for example, to make aircraft cockpit visualization devices.

The night vision binoculars amplification devices have a significant amplification coefficient in a spectral band starting at the red end of the visible spectrum, around 650 nanometers and ending in the near infrared, around 930 nanometers. The diodes emitting in the green or in the blue are naturally compatible NVG, their emission in the red or near infrared being very weak or non-existent. It is not the same for red emitting diodes that must be filtered so as not to saturate the binoculars.

There are different types of NVG-compatible backlighting.

A first solution is to use NVG-compatible red light sources whose emission in the higher wavelengths of red is therefore reduced. Thus, the patent EP 1 974 190 entitled "Night vision compatible display backlight" of the company "Astronautics Corporation of America" provides lighting with NVG-compatible "orange" diodes. The main disadvantage of this solution is that the colorimetry of the "day" image is substantially modified.

A second solution is to have an NVG filter covering all the emitter diodes. We find the previous disadvantage. A variant of this solution consists in arranging the filters only red-emitting diodes to achieve the best possible compromise between NVG compatibility and colorimetry. Patent FR 2 942 023 of the Applicant entitled "NVG-compatible light-emitting diode lighting device" proposes a technical solution of this type.

A third solution is to have specific lighting independent of the daylight to ensure NVG lighting. EP 0 560 614 from Kaiser Aerospace & Electronics Corporation entitled "Backlight for a liquid crystal display" proposes a solution of this type. The mixture of light sources is provided by a prismatic light guide. This solution preserves daytime colorimetry. However, it has a larger footprint than previous devices and requires the addition of optical components.

In general, backlightings can be grouped into two architectures. The first architecture consists in forming a carpet of light-emitting diodes arranged directly under the liquid crystal matrix to be illuminated.

The second architecture is to illuminate a light guide by the edge. It is shown in Figures 1 and 2. Figure 1 shows an exploded view of the various components of the backlighting, Figure 2 shows a partial sectional view in the plane of the light diodes. Backlighting 1 then comprises:

a light guide 10 of substantially parallelepipedal or prismatic shape, of small thickness, arranged under the liquid crystal matrix 20 to be illuminated;

an illumination consisting of light-emitting diodes 1 1 arranged in line;

a supply circuit 12 for the light-emitting diodes;

a mechanical structure 1 3 which carries the supply circuit 12 and the lighting diodes 1 1.

For this lighting to be NVG compatible, a possible technical solution is to have an NVG filter on some red emitting diodes. Figure 3 shows a view in the previous section plane of this implantation. In this FIG. 3, the diodes 14 filtered are shown in black and are surmounted by a filter 15 shown schematically by a white rectangle. This technical solution has the following defects:

- The size of the filtered LEDs is greater than those of the unfiltered LEDs. This size imposes that the light guide is away from the bar LEDs daylight. This causes a loss of luminous efficiency of the lighting system for daylight mode where this parameter is very important;

- It is necessary that the NVG LED filtering is perfectly efficient and there is no light leakage outside the filter. It is therefore important that the NVG LED be surrounded by a light absorbing area that does not pass through the filter. A black body or the addition of a black cap around the LED is then necessary. o The presence of this absorbing element increases the spacing between the diodes and reduces the number, which limits the number of LEDs used in normal mode and therefore reduces the light output of the backlighting day; o The presence of this absorbent element near the LEDs of the normal mode also impairs the injection efficiency of the

Normal mode LEDs in the light guide absorbing part of the luminous flux of these LEDs.

The lighting device according to the invention does not have these disadvantages. More specifically, the invention relates to a compatible lighting device for the use of night vision binoculars, said lighting device comprising at least:

a row of first light-emitting diodes carried and fed by an electronic circuit;

a second light-emitting diode surmounted by an optical filter, said optical filter having a spectral transmission such that the light coming from the second diode filtered by said filter is compatible with the use of said night-vision binoculars,

characterized in that the illumination device comprises a light guide comprising an input face disposed in front of the second diode filtered electroluminescent array, a light guide zone whose length is equal to that of the row of first light-emitting diodes and a plurality of diffusing output faces disposed at and between the first light-emitting diodes.

Advantageously, the light guide is substantially in the form of a thin planar blade and elongate shape, the second filtered LED is arranged along a slice of the planar blade.

Advantageously, the thin planar blade comprises hollow housing, the first light-emitting diodes being disposed in said hollow housing.

Advantageously, the thin planar blade comprises slots, the first light-emitting diodes being disposed between said slots.

Advantageously, the thin planar blade is substantially in the form of a right prism with triangular faces, each triangular face having the shape of an elongated rectangle triangle, the second filtered electroluminescent diode being disposed along the short side of the right triangle, the row of first electroluminescent diodes being arranged along the long side of the right triangle.

Advantageously, the light guide comprises at least one reflective cutaway disposed between the light guide zone and one of the diffusing exit faces.

Advantageously, the light guide comprises two reflective cut faces disposed between the light guide zone and one of the diffusing outlet faces, the two cut faces forming a triangular prism.

Advantageously, the light guide comprises at least one butt-shaped portion disposed between the light-guiding zone and one of the diffusing exit faces.

Advantageously, the light guide is substantially in the form of a right prism with trapezoidal faces, each face having the shape of an isosceles trapezium, the second filtered electroluminescent diode being disposed along the small base of the trapezium, the row of first light-emitting diodes. being arranged along the large base of the trapezium. Advantageously, each slot has a triangular notch so that the light guide consists of a plurality of secondary optical guides, each secondary guide leading the light from the second diode filtered between two first light emitting diodes.

Advantageously, the light guide comprises, apart from the ^inlet face and the faces of diffusing outputs, a reflective treatment on at least one of its faces.

Advantageously, the second light-emitting diode is of the same type as at least one of the first light-emitting diodes.

Advantageously, the second electroluminescent diode is partially masked so that its emitting surface is adapted to the surface of the input face.

Advantageously, the electronic circuit is a flexible printed circuit carrying both the first light-emitting diodes and the second light-emitting diode, the second diode being in a different plane from that of the first light-emitting diodes.

The invention will be better understood and other advantages will become apparent on reading the description which follows given by way of non-limiting example and by virtue of the appended figures among which:

Figure 1 shows an exploded view of a backlighting having a daylight;

Figure 2 shows a partial sectional view of said daylight backlighting;

3 shows a partial sectional view of a backlighting comprising NVG-compatible lighting according to the prior art;

FIG. 4 represents a partial sectional view in a first plane of a first backlighting comprising NVG-compatible lighting according to the invention;

Figure 5 shows a partial sectional view in a second plane of the first backlighting;

FIG. 6 represents a partial sectional view in the first plane of a first variant of the first backlighting; Figure 7 shows a partial sectional view in the first plane of a second variant of the first backlighting;

FIG. 8 represents a partial sectional view in the first plane of a third variant of the first backlighting;

FIG. 9 represents a partial sectional view in the first plane of a fourth variant of the first backlighting;

FIG. 10 represents an electronic supply circuit for a backlighting comprising NVG-compatible lighting according to the invention;

FIG. 11 represents a partial sectional view in the second plane of a second backlighting comprising NVG-compatible lighting according to the invention;

FIG. 12 represents a partial sectional view in the second plane of a variant of the exit zone of this second backlighting;

Figure 13 shows a partial sectional view in the second plane of a first variant of the second backlighting.

The different figures are represented in an oriented reference (X, Y, Z). The plane (X, Y) corresponds to the plane of the main light guide disposed under the liquid crystal matrix to be illuminated. The X axis corresponds to the main axis of the array of light emitting diodes. The Z axis is perpendicular to the (X, Y) plane. In these different figures, the main light guide is not shown.

As a first nonlimiting example, FIGS. 4 and 5 show two partial sectional views in the (X, Z) and (X, Y) planes of a first backlighting comprising NVG compatible lighting according to the invention. This lighting device comprises at least:

- A row of first light emitting diodes 1 1 carried and supplied by an electronic circuit 12. These diodes 1 1 are intended to provide daylight main illumination. Generally, they emit in three different spectral ranges so as to ensure white lighting. The electronic circuit 12 is generally a flexible printed circuit or "flex";

a second electroluminescent diode 14 surmounted by an optical filter 15, the optical filter having a spectral transmission such as that the light from the second filtered diode 14 is compatible with the use of said night vision binoculars. This diode emits in the red part of the spectrum and the filter cuts the radiation located beyond a certain wavelength. This diode may be of the same type as the red diodes of the row of diodes 1 1 used for the main illumination. Generally, this second diode is powered by the same electronic supply circuit 12 which is a flexible circuit called flex. By adjusting the shape and flexibility of the flex, as illustrated in FIG. 10, it is indeed possible to arrange the second diode in a plane different from that of the first row of light-emitting diodes; a light guide 16 comprising:

an input face 161 disposed in front of the second filtered light-emitting diode 14. The second light-emitting diode 14 may have an emitting surface of dimensions greater than those of said input face. In this case, the second light-emitting diode is partially masked so that its emitting surface is adapted to the surface of the input face and no stray light disturbs the proper operation of the optical guide;

a guide zone 162 of the light whose length is equal to that of the row of first light-emitting diodes. In the example of FIGS. 4 and 5, the guiding zone is substantially in the form of a thin, elongated planar blade, the second filtered LED being disposed along a wafer of this planar blade. The propagation of light rays inside the light guide is essentially by total reflections on the walls of the guide. To increase its efficiency, this guide zone may be wholly or partly metallized;

a plurality of diffusing output faces 163 disposed at and between the first light-emitting diodes 1 1. These faces 163 are represented by striped areas on the different figures. Diffusion zones 163 can be obtained in different ways. For example, we can depolish these areas. One can also add microstructures that will deflect the light flowing in the guide to the entrance of the main light guide.

In the example of FIGS. 4 and 5, the thin planar blade comprises hollow housings 164, the first light-emitting diodes 1 1 being disposed in said hollow housings. In this example and in the following, the various figures comprise a single filtered light-emitting diode, for the sake of clarity of the figures. It is, of course, possible to have several filtered diodes to obtain more light or a better homogeneity of lighting or improve the reliability of the backlighting.

There are different variant configurations of this first backlighting. Figure 6 shows a first variant. The light guide has a notch 165 in which the electroluminescent diode 14 and its filter 15 are housed.

FIG. 7 represents a second variant of the device of FIGS. 4 and 5. In this variant, the guide zone comprises a series of slots 166 between which the first light-emitting diodes 1 1 are arranged.

FIG. 8 represents a third variant of the device of FIGS. 4 and 5. In this variant, the thin planar blade 162 is substantially in the form of a right prism with triangular faces, each triangular face having the shape of an elongated rectangle, the second filtered electroluminescent diode 14 being disposed along the short side of the right triangle, the row of first light emitting diodes 1 1 being arranged along the long side of the right triangle. This blade shape facilitates the propagation of light rays from the second filtered diode. As can be seen in FIG. 8, these light rays, symbolized by hatched arrows, are reflected, by total reflection, on the hypotenuse 167 of the triangular face. In this figure 8, the guide zone also comprises a series of slots 166 between which are arranged the first electroluminescent diodes 1 1. In an alternative embodiment, the diodes can also be arranged in housings.

FIG. 9 represents a fourth variant of the device of FIGS. 4 and 5. In this variant, the thin planar blade is simply arranged under the row of the first light-emitting diodes 1 1, which simplifies the shape of the blade which no longer comprises any housing nor slots.

To reduce clutter, the light guide may include a reflective cutaway disposed between the light guide zone and each exit face. It may also comprise two reflective cut faces disposed between the light guide zone and each exit face, the two cut faces forming a triangular prism.

In the backlighting of FIGS. 4 to 9, the injection of the filtered light is made on one of the lateral sides of the row of the first light-emitting diodes 1 1. One of the difficulties of this configuration is to illuminate the output faces 163 located between these first light-emitting diodes in a homogeneous manner.

As a second nonlimiting example, FIGS. 11, 12 and 13 show a second embodiment of a backlighting according to the invention used in longitudinal mode. In this configuration, the NVG light guide is disposed under the main light guide disposed in front of the daylighting diodes 1 1. The light guide 17 may comprise cut-off lugs 170 making it possible to fold the light beams coming from the filtered diode towards crenels 174 placed between the first light-emitting diodes 1 1.

In the two sectional views of FIG. 11 made in the planes (X, Y) and (Y, Z), the light guide 17 is substantially in the form of a right prism with trapezoidal faces, each face being in the form of an isosceles trapezoid, the second filtered light emitting diode 14 being disposed along the small base 171 of the trapezium, the row of first light-emitting diodes 1 1 being arranged along the large base 172 of the trapezium. The hatched arrows represent the path of the light rays coming from the source 14. The base 171 may comprise a diffusing treatment or an array of diffusing patterns 173 making it possible to improve the diffusion and propagation of the light rays in the light guide.

As seen in FIG. 12, the light guide may also include one or more curved butt-shaped portions 177 disposed between the light guiding region and the diffusing exit faces. The cross section may be rectangular or circular.

To improve the transport and distribution of the light rays ^up to areas between the first emitting LEDs 1 1, each slot 174 may comprise a triangular notch 175 as shown in Figure 13. The light guide is then composed of a plurality of secondary optical guides 176 in the form of thin blades spread fanwise, each secondary guide leading, by total reflection on the walls of the secondary guide, the light from the second filtered diode 14 between two first light emitting diodes 1 1. The hatched arrows represent the path of the light rays from the filtered source 14. The advantages of the backlightings according to the invention are as follows:

- Keep without modification, the main guide of light emitting diodes in normal mode. This preserves all the injection efficiency of the daylighting diodes;

- Get a small footprint of the entire backlighting;

- Use a reduced number of NVG-compatible light-emitting diodes;

- Obtain homogeneous lighting;

- Use only one power flex and one additional light guide for night lighting.

Claims

1. A lighting device (1) compatible with the use of night vision binoculars, said lighting device comprising at least:

a row of first light-emitting diodes (1 1) carried and supplied by an electronic circuit (12);

a second light-emitting diode (14) surmounted by an optical filter (15), said optical filter having a spectral transmission such that the light coming from the second diode filtered by said filter is compatible with the use of said night-vision binoculars,

characterized in that the illumination device comprises a "NVG" light guide (16, 17) comprising an input face (161, 171) disposed in front of the second filtered LED, a guide region (162) of the light having a length equal to that of the array of first light-emitting diodes and a plurality of diffusing output faces (163) disposed at and between the first light-emitting diodes.

2. Lighting device according to claim 1, characterized in that the light guide (16) has substantially the shape of a thin planar blade and elongated shape, the second filtered light emitting diode being disposed along a wafer of the flat blade.

3. Lighting device according to claim 2, characterized in that the thin planar blade comprises hollow housings (164), the first light-emitting diodes being disposed in said hollow housing.

4. Lighting device according to claim 2, characterized in that the thin planar blade comprises crenellations (166), the first light-emitting diodes being disposed between said crenellations.

5. Lighting device according to claim 2, characterized in that the thin planar blade is substantially in the form of a right prism with triangular faces, each triangular face having the shape of a right triangle. elongated, the second filtered LED being disposed along the short side of the right triangle, the row of first light emitting diodes being disposed along the long side of the right triangle.

6. Lighting device according to claim 1, characterized in that the light guide (17) comprises at least one reflective cutaway disposed between the light guide zone and one of the diffusing outlet faces.

7. Lighting device according to claim 6, characterized in that the light guide (17) comprises at least two reflective cut faces disposed between the light guide zone and one of the diffusing outlet faces, the two cut panes. forming a triangular prism (170).

8. Lighting device according to claim 1, characterized in that the light guide comprises at least one butt-shaped portion (177) disposed between the light guide zone and one of the diffusing exit faces.

9. A ^lighting equipment according to claim 4, characterized in that the light guide (17) is substantially in the shape of right prism with trapezoidal faces, each face having the shape of an isosceles trapezium, the second light emitting diode being filtered disposed along the small base (171) of the trapezoid, the row of first light-emitting diodes being arranged along the large base (172) of the trapezium.

10. Lighting device according to claim 9, characterized in that each slot has a triangular notch (175) so that the light guide is constituted by a plurality of secondary optical guides (176), each secondary guide leading to light from the second diode filtered between two first light emitting diodes.

1 1. Lighting device according to one of the preceding claims, characterized in that the light guide comprises, outside the input face and the diffusing output faces, a reflective treatment on at least one of its faces.

12. Lighting device according to one of the preceding claims, characterized in that the second light-emitting diode is of the same type as at least one of the first light-emitting diodes.

13. Lighting device according to one of the preceding claims, characterized in that the second light-emitting diode is partially masked so that its emitting surface is adapted to the surface of the input face.

14. Lighting device according to one of the preceding claims, characterized in that the electronic circuit (12) is a flexible printed circuit carrying both the first light-emitting diodes and the second light-emitting diode, the second diode being in a plane different from that of the first light-emitting diodes.