Backlighting device for display screen by night-vision compatible transmission

• US 20040057226A1
• Filed: 07/23/2003
• Published: 03/25/2004
• Est. Priority Date: 01/26/2001
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Berthou, Nicolas, Breda, Jean-Marc
• Granted Patent: US 6,847,173 B2
• Time in Patent Office: Days
• US Class Current: 362/31
• CPC Class Codes: B60Q 3/14 lighting through the surface to be illuminated
• CPC Class Codes: B60Q 3/18 for varying the light intensity
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133613 characterized by the sequence of light sources
• CPC Class Codes: G02F 1/133626 providing two modes of illumination, e.g. day-night

Abstract

The present invention relates to a backlighting device, having several brightness levels, for a transmission display screen (12). The device comprises light sources placed in a case (14) between a translucent front wall formed by a diffuser screen (20) and a rear wall (24). The light sources, selected according to the desired brightness level, are mosaics (24, 28) of light-emitting diodes (26, 30) that are placed immediately behind the diffuser screen with, for the highest brightness level, a first mosaic (24) of light-emitting diodes that provides daytime illumination and with, for the lowest brightness level, a second mosaic (28) of light sources that supplies night-time illumination.

Application: light box for transmission display screens

Claims

1. A backlighting device, having several brightness levels, for a transmission display screen (12), comprising light sources placed in a case (14) between a translucent front wall formed by a diffuser screen (20) and a rear wall (21), the light sources being selected according to the desired brightness level, characterized in that the light sources are mosaics (24, 28) of light-emitting diodes (26, 30) that are placed immediately behind the diffuser screen with, for the highest brightness level, a first mosaic (24) of light-emitting diodes that provides daytime illumination and with, for the lowest brightness level, a second mosaic (28) of light sources that supplies night-time illumination.

2. The backlighting device as claimed in claim 1, characterized in that the first mosaic (24) and the second mosaic (28) of light-emitting diodes lie in the same plane, the light-emitting diodes being wired to the same printed circuit (22) that includes electrical conductors for supplying current to the diodes.

3. The backlighting device as claimed in either of claims 1 and 2, characterized in that each mosaic (24, 28) is formed from a defined number of arrays (DB1, DB2, . . . DBn)(DV1, DV2, . . . DVp) of light-emitting diodes, the light intensity of the light-emitting diodes of an array being adjusted by controlling the current through the diodes by a semiconductor (TB1, TB2, . . . TBn)(TV1, TV2, . . . TVn).

4. The backlighting device as claimed in claim 3, characterized in that the diodes of an array of light-emitting diodes in series with a semiconductor are preferably dispersed over the mosaics (24, 28).

5. The backlighting device as claimed in one of claims 1 to 4, characterized in that the light box includes an infrared filter (32) between the diffuser (20) and the mosaics (24, 28) of diodes that further reduces the low amount of infrared radiation able to be produced by the second mosaic (28) of diodes.

6. The backlighting device as claimed in claim 5, characterized in that the infrared filter (32), between the diffuser (20) and the diodes, and in immediate proximity to the mosaics of light-emitting diodes, comprises a mosaic of holes (40) having the same distribution as the first mosaic (24) of light-emitting diodes, each of the light-emitting diodes of the first mosaic (24) facing a respective hole (40) of the infrared filter.

7. The backlighting device as claimed in one of claims 2 to 6, characterized in that the distribution of diodes on the printed circuit (22) is regular, of the honeycomb type, the diodes of the two mosaics (24, 28) interpenetrating with a regular pitch, a line Ln of light-emitting diodes comprising only diodes of the first mosaic, the next line L(n+1) or the previous line L(n−

1) comprising a series of alternating diodes of the first and second mosaics.

8. The backlighting device as claimed in one of claims 2 to 7, characterized in that the printed circuit (22) includes drive electronics (34) for turning on the diodes.

9. The backlighting device as claimed in one of claims 1 to 8, characterized in that it includes a supply circuit (50) for the first mosaic (24) and the second mosaic (28) of light-emitting diodes, the diodes of the two mosaics being grouped together in an array of a small number of diodes, the array including an input and an output.

10. The backlighting device as claimed in claim 9, characterized in that the supply circuit (50) includes a supply line La supplying, via first current-limiting resistors (RB1, RB2, . . . RBn), the respective inputs of n arrays (DB1, DB2, . . . DBn) of a number J of light-emitting diodes per array of the first mosaic (24) and, via second current-limiting resistors (RV1, RV2, . . . RVp), the respective inputs of p arrays (DV1, DV2, . . . DVp) of a number K of light-emitting diodes per array, each array of diodes being connected, via a respective semiconductor (TB1, TB2, . . . TBn) for the first mosaic (24) and (TV1, TV2, . . . TVp) for the second mosaic (28), to a reference potential (M), each semiconductor including a control input EC1 for the semiconductors of the first mosaic and a control input EC2 for the semiconductors of the second mosaic, allowing the current in the arrays of diodes to be varied.

11. The backlighting device as claimed in claim 10, characterized in that the semiconductor is a field-effect transistor.

12. The backlighting device as claimed in either of claims 10 and 11, characterized in that the J diodes and K diodes of each of the arrays of diodes are connected in series, it being possible for the loss of a diode of an array DBx, where x=1,2, . . . n, or DVy, where y=1,2, . . . p, to cause at most the extinction of only the diodes of the array DBx or DVy.

13. The backlighting device as claimed in one of claims 2 to 12, characterized in that the printed circuit (22) comprises a honeycomb distribution of light-emitting diodes and in that, considering a part (60) of the printed circuit (22) to comprise eight lines of eight light-emitting diodes each referenced DIc, I being the rank of the diode along a line and c the rank of the line, the distribution of the diodes is such that, when a line comprises only diodes of the first mosaic (24), the next or previous line comprises an alternation of a diode of the first mosaic (24) and a diode of the second mosaic (28) and so on, the first line being a line of the first mosaic, the second and sixth lines starting with a diode of the second mosaic.

14. The backlighting device as claimed in claim 13, characterized in that, in a first distribution of the diodes of a diode array of the part (60) in question of the printed circuit (22):

the array of the second mosaic (28) comprises four diodes, the diodes D23, D46, D63 and D86 being connected in series, the distribution being repeated by a horizontal translation along the lines forming arrays of the second mosaic that relate to this part (60) of the printed circuit (22); and

the array of the first mosaic (24) comprises four diodes, the diodes D22, D45, D62 and D85 being connected in series, the distribution being repeated by a horizontal translation along the lines forming arrays of the first mosaic (.24) that relate to this part (60) of the printed circuit (22).

15. The backlighting device as claimed in claim 13, characterized in that, in a second distribution of the diodes of a diode array of the part (60) in question of the printed circuit (22):

the array of the second mosaic (28) comprises four diodes, the diodes D23, D44, D63 and D84 being connected in series, this distribution being repeated by a horizontal translation along the lines forming arrays of the second mosaic that relate to this part (60) of the printed circuit (22); and

the array of the first mosaic (24) comprises four diodes, the diodes D12, D33, D52 and D73 (or D22, D43, D62 and D83) being connected in series, this distribution being repeated by a horizontal translation along the lines forming arrays of the first mosaic (24) that relate to this part (60) of the printed circuit (22).

16. The backlighting device as claimed in one of claims 13 to 15, characterized in that the combination of the array of the first mosaic (24) and the array of the second mosaic (28) is obtained by considering the entire surface of the printed circuit (22).