Illuminated Light Box With Light-Emitting Diodes

• US 20080062116A1
• Filed: 09/06/2005
• Published: 03/13/2008
• Est. Priority Date: 09/28/2004
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Morbieu, Bertrand, Chaillou, David
• Granted Patent: US 8,215,818 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/32 Pulse-control circuits

Abstract

The invention relates to a light box, intended especially for the backlighting of liquid crystal displays. The box includes a lightguide in the form of a thin plate having two opposed main faces and at least two edges, the lightguide having a light-diffusing optical structure on one of the faces. Light-emitting diodes are placed linearly along at least one of the edges of the lightguide, the light emitted by the light-emitting diodes illuminates the lightguide via the edge, and is being diffused by that face of the lightguide having the optical structure. The light-emitting diodes placed along each of the edges of the lightguide are organized in at least two rows and in such a way that a light-emitting diode in one row supplied by an electric power supply (S1 to S8) is immediately followed by a light-emitting diode in the other row supplied by another electric power supply.

Claims

1. A light box, intended especially for the backlighting of liquid crystal displays, the box comprising:

a lightguide in the form of a thin plate having two opposed main faces and at least two edges, the lightguide having a light-diffusing optical structure on one of the faces;

light-emitting diodes placed linearly along at least one of the edges of the lightguide, the light emitted by the light-emitting diodes which illuminates the lightguide via the edge being diffused by that face of the lightguide having the optical structure;

wherein the light-emitting diodes placed along each of the edges of the lightguide are organized in at least two rows and in such a way that a light-emitting diode in one row supplied by an electric power supply is immediately followed by a light-emitting diode in the other row supplied by another electric power supply.

2. The light box as claimed in claim 1, comprising at least one photodetector delivering a luminous intensity signal corresponding to the light emitted by the box.

3. The light box as claimed in claim 2, wherein the luminous intensity data output by the photodetector is transmitted to a device for controlling or servocontrolling the luminance of the light box.

4. The light box as claimed in claim 1, wherein the LEDs of at least one of the branches (or rows) emits a light spectrum different than that of the other branches.

5. The light box as claimed in claim 4, comprising three photodetectors provided with color filters, respectively, for capturing the light radiation of the light box in the red, green and blue colors so as to produce signals for chromatically balancing the rows of light-emitting diodes.

6. The light box as claimed in claim 4, comprising a lightguide of rectangular shape having four edges and eight rows of light-emitting diodes, one pair of diode rows illuminating a respective edge of the lightguide.

7. The light box as claimed in, claim 1, comprising:

a case having a bottom and an opening facing the bottom of the case, in particular for the backlighting of a liquid crystal display;

on the bottom side of the case, a printed circuit parallel to the bottom of the case; and

a lightguide having, on one of the faces turned toward the bottom of the case, an optical structure for diffusing the light propagating in the lightguide, the printed circuit having, on one of its faces, on the lightguide side, a reflector for reflecting, onto the openings, the light diffused by the optical structure of the lightguide, the printed circuit of the light box comprising eight rows Rb1, Rb2, . . . Rb8, of seven LEDs Lnm in series, n being the number of the row from 1 to 8, and m being the number of the LED in each row, the rows being aligned in pairs on each of the edges B1, B2, B3, B4 of the lightguide, respectively, rows Rb1 and Rb2 illuminating the edge B1, rows Rb3 and Rb4 illuminating the edge B2, rows Rb5 and Rb6 illuminating the edge B3 and rows Rb7 and Rb8 illuminating the edge B4.

8. The light box as claimed in claim 7, wherein each of the rows Rb1, Rb2, . . . Rb8 of the LEDs is supplied by an independent power supply S1, S2, . . . S8 respectively and in that, for a given edge of the lightguide, a light-emitting diode Lnm in a row Rbn supplied by an electric power supply is immediately followed by a light-emitting diode L(n+1)m in the other row Rb(n+1) supplied by another electric power supply;

thus, the LEDs in rows Rb1 and Rb2 are interleaved in such a way that the LED L11 in row Rb1 is immediately followed by the LED L21 in row Rb2, then the latter by the LED L12 in row Rb1 and so on until the last LED L28 in row R2 terminating the illumination of the edge B1 of the lightguide, the other edges B2, B3 and B4 having the LEDs of the other branches, Rb3, Rb4;

Rb5, Rb6; and

Rb7, Rb8, respectively, in the same configuration.

10. The light box as claimed in claim 7, comprising a printed circuit having a photoelectric sensor receiving the light diffused by the diffusing optical structure of the lightguide through the hole in the opaque coating and the central hole in the printed circuit, the photoelectric sensor delivering electrical data Up as a function of the luminous intensity of the light box illumination.

11. The light box as claimed in claim 10, wherein the electrical data Up output by the photoelectric sensor is transmitted, after being digitized, to a microprocessor connected to a control device for controlling the power delivered by the supplies S1 to S8 for rows Rb1 to Rb8 of the LEDs of the light box, the data Up output by the photoelectric sensor being used by the microprocessor in order to act on the control device so as to maintain the luminous intensity in the light box within a specified range of possible illumination levels output by the LEDs.

12. The light box as claimed in claim 1, wherein, when the rows of LEDs are supplied with a periodic signal in the form of rectangular pulses, the illumination output by the light-emitting diodes is controlled by varying the duty cycle of the rectangular pulses.

13. The light box as claimed in claim 7, comprising three photoelectric sensors each having a respective red filter, green filter nd blue filter, the sensors receiving, via the hole in the coating and the hole n the printed circuit of the light box, the light diffused by the lightguide.

14. The light box as claimed in claim 12, wherein the electrical data output by each of the three photodetectors corresponding to the respective red, green and blue levels of the spectrum emitted by the light box is sent, after being digitized, to the input of a microprocessor connected to a control device for controlling the power delivered by the supplies S1 to S8 for rows Rb1 to Rb8 of the LEDs of the light box of each row of LEDs emitting a different color spectrum, the microprocessor being configured by a memory for driving the various rows of LEDs in such a way that the spectrum of the light output by the box is as close as possible to the desired color, for example the color white, and to the desired luminous intensity.

15. The light box as claimed in claim 1, wherein the rows of LEDs themselves are covered by a near-infrared optical filter, in the form of a mask, over the entire length of the branches of LEDs.

16. The light box as claimed in claim 1, wherein the rows of LEDs are molded with a material that filters out near-infrared radiation.

17. The light box as claimed in claim 1, wherein the LEDs are wired to the printed circuit so as to emit light radiation perpendicular to the faces of the lightguide, the rows of diodes being encased in a small case of the length of the rows, said small case being closed in its upper part by a longitudinal near-infrared optical filter, a mirror along the entire length of the branches and inclined at 45°

to the faces of the lightguide, reflecting the filtered light emitted by the rows of LEDs onto the respective edges B1, B2, B3 and B4 of the lightguide.

18. The light box as claimed in claim 1, wherein comprising a stack of light-emitting diode branches and waveguides associated with each set of branches in any one plane.

19. The light box as claimed in claim 18, comprising a first stage E1 having first branches Rb1 to Rb8 of LEDs wired to a first printed circuit having a reflector and its first associated lightguide and a second stage E2 having second branches Rb′

1 to Rb′

8 wired to a second printed circuit, which is open over the entire surface area of the first lightguide so as to let through all of the light from the two stages that is reflected by the reflector of the first stage E1 and a second lightguide associated with the second branches Rb′

1 to Rb′

8.

9. The light box as claimed in wherein it includes, on the bottom side of the case, a printed circuit parallel to the bottom of the case and pierced by a central hole, the lightguide having, on one of the faces turned toward the bottom of the case, an optical structure for diffusing the light propagating in the lightguide, the printed circuit being coated, on one of its faces, on the side facing the lightguide, with a translucent white film and with a diffusing opaque coating having a hole in the coating coaxial with the axis of the central hole of the printed circuit.