Backlighting device for the display screen of a television or mobile phone

Abstract

Backlighting device for a screen for a television, mobile phone or the like, wherein the backlighting device comprises: a first light source adapted to emit light having a peak wavelength between 600 and 630 nm; a second light source adapted to emit light having a peak wavelength between 510 and 530 nm; a third light source adapted to emit light having a peak wavelength between 440 and 460 nm; wherein the light emitted by one of the light sources has a bandwidth of less than 15 nm, preferably less than 10 nm, more preferably less than 5 nm.

Claims

1. A backlighting device for a screen for a television, mobile phone or the like, wherein the backlighting device comprises: a first light source adapted to emit light having a peak wavelength between 600 and 630 nm; a second light source adapted to emit light having a peak wavelength between 510 and 530 nm; a third light source adapted to emit light having a peak wavelength between 440 and 460 nm; wherein the light emitted by one of the light sources has a bandwidth of less than 15 nm, preferably less than 10 nm, more preferably less than 5 nm.

2. The backlighting device according to claim 1, wherein light emitted by the second light source has a bandwidth of less than 15 nm, preferably less than 10 nm, more preferably less than 5 nm.

3. The backlighting device according to claim 1, wherein the light emitted by each of the light sources has a bandwidth of less than 15 nm, preferably less than 10 nm, more preferably less than 5 nm.

4. The backlighting device according to claim 1, wherein the light emitted by the light sources forms peaks which are spectrally symmetric.

5. The backlighting device according to claim 1, wherein the backlighting device provides a spectral power distribution with a spectral power at 555 nm which is less than 50%, preferably less than 20%, more preferably less than 10% of the spectral power at the peak wavelength of the first light source.

6. The backlighting device according to claim 1, wherein the backlighting device comprises a plurality of clusters, each of which comprises a first light source, a second light source and a third light source.

7. The backlighting device according to claim 1, wherein the three light sources are positioned in an array, preferably a rectangular array.

8. The backlighting device according to claim 1, wherein at least one of the light sources is a LED light source or wherein all light sources are LED light sources.

9. The backlighting device according to claim 1, wherein at least one of the light sources is a VCSEL light source or wherein all of the light sources are VCSEL light sources.

10. The backlighting device according to claim 1, wherein the third light source is a LED light source and the second light source is a VCSEL light source, and preferably wherein the first light source is a VCSEL light source.

11. The backlighting device according to claim 1, wherein the backlighting device is adapted to emit light in a spectral power distribution with an S/P ratio of between 2 and 5.

12. The backlighting device according to claim 1, wherein the CCT of the spectral power distribution is between 6000 and 7000 K, preferably around 6500 K.

13. The backlighting device according to claim 1, wherein the backlighting device has a spectral power distribution with a maximum spectral power and the spectral power in the range between 470 and 490 nm is less than 15% of the maximum spectral power, preferably with a minimum spectral power of less than 5% of the maximum spectral power.

14. The backlighting device according to claim 1, wherein the backlighting device has a spectral power distribution with a maximum spectral power and the spectral power in the range between 550 and 590 nm is less than 15% of the maximum spectral power, preferably with a minimum spectral power of less than 10% of the maximum spectral power.

15. A screen for a television, mobile phone or the like, comprising the backlighting device according to claim 1.

16. The screen according to claim 15, wherein the screen is an LCD screen comprising a screen plane for displaying an image, the screen comprising a pixel array with for each pixel three liquid crystals and three colour filters, such as TFTs, corresponding to the first, second and third light sources, and wherein the backlighting device is configured to emit light towards the pixel array, and wherein the liquid crystals are aligned with the colour filters so as to determine the transmission of light from the backlighting device towards the front plane.

17. The screen according to claim 16, wherein the screen further comprises a processing device for converting a digital image to a collection of desired pixel colours, and a controller for controlling the transmission of the liquid crystals, wherein the processing device is configured to communicate the collection of desired pixel colours to the controller, and wherein the controller is configured to adapt the transmission of the liquid crystals in each pixel to transmit light through a subset of the colour filters, such that each pixel emits a desired colour according to the collection of desired pixel colours.

18. The screen according to claim 16, wherein each filter is configured to transmit substantially no light coming from light sources other than the light source it corresponds to.

19. The screen according to claim 16, wherein the screen further comprises a diffuser for scattering the light emitted by the backlighting device, to increase the uniformness of directional and spatial distribution of the light, wherein the diffuser is placed between the backlighting device and the liquid crystals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The features and advantages of the invention will be further appreciated upon reference to the following schematic drawings of a number of exemplary embodiments, in which corresponding reference symbols indicate corresponding parts.

[0040] FIG. 1A schematically shows a front view of a television screen according to an embodiment;

[0041] FIG. 1B schematically shows a cross-section of part of a television screen according to an embodiment;

[0042] FIG. 2 schematically shows a spectral distribution of a lighting device according to the prior art;

[0043] FIG. 3 schematically shows a spectral distribution of a screen or lighting device according to an embodiment of the invention;

[0044] FIG. 4A schematically shows a spectral distribution of a screen or lighting device according to an embodiment of the invention;

[0045] FIG. 4B schematically shows a colour space or gamut corresponding to the spectral distribution in FIG. 4A;

[0046] FIG. 5 again schematically shows the spectral distribution of FIG. 4A, together with exemplary filter characteristics.

[0047] The figures are for illustrative purposes only, and do not serve as a restriction on the scope or the protection as laid down by the claims.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0048] FIG. 1A schematically shows a front view of an LCD television screen 1 according to an embodiment, placed in a casing 2 in which the screen 1 is mounted. The screen includes a pixel array 3 (only partly shown) built up of an array of pixels of which the colour can be set individually. In order to show an image on the screen 1, a digital image (delivered by for instance a network server, a digital memory or a computer) is converted by a processing device 4 to a collection of colours corresponding to the pixels in the pixel array 3. The processed image is communicated to a controller 5 which controls the individual colours of each pixel in the pixel array 3. Processing device 4 and controller 5 are preferably incorporated in the casing 2 of the screen 1 itself, for instance at the back side of the screen. Alternatively, they are separate from the screen 1 but are able to communicate with the relevant parts of the screen 1, in particular the pixel array 3 or specifically the liquid crystals.

[0049] FIG. 1B schematically shows a cross-section of a part of the LCD television screen. The figure shows a cross-section of a part of a screen 1, excluding the casing in which the screen is mounted. At the back side, the screen 1 comprises a backlighting device 10 including an array 11 of clusters 19 which each comprise a first light source 12, a second light source 14 and a third light source 16. The light emitted from the lighting device passes through a diffuser 18 towards the liquid crystals 30. The diffuser ensures that the light from the various light sources is mixed, such that the colours are spatially and directionally uniformly distributed over the screen. The liquid crystals 30 and filters 40 are divided by subpixel 31a, 31b, 31c, 32a, 32b, 32c, 41a, 41b, 41c, 42a, 42b, 42c so as to be able to vary the colours by controlling the transmission through each filter 40 by means of its corresponding liquid crystal 30. Three subpixels of the three different colours form a pixel 31, 41 in the pixel array. The liquid crystals 30 and filters 40 are sandwiched in between mutually perpendicular polarisers 20, 50. At the front side, a transparent cover layer 60 limits the screen 1. The person skilled in the art will understand that many variations to the screen's components and layers can be conceived which are compatible with the invention. In the illustrated case, the three types of light sources 12, 14, 16 in the lighting device 10 are mounted in clusters 19 in an array 11 behind the liquid crystals 30. Alternatively, the clusters 19 may be placed only at the edges of the screen 1, emitting into a waveguide which corresponds to the entire screen surface. In another alternative embodiment, the light sources may not be clustered. The working of exemplary backlit LCD screens has been explained in more detail for instance in U.S. Pat. No. 6,243,068, which is incorporated herein by reference in its entirety.

[0050] FIG. 2 schematically shows a spectral distribution 200 of a lighting device according to the prior art. This spectrum is generated by a white, phosphor conversion (PC) LED. The blue peak 215 corresponds to the blue LED which excites the phosphor of which the phosphor emission peak 213 is centred around 555 nm. The blue peak 215 is weakened by means of a yellow filter, which leads to a loss of efficiency. It is clear from the spectrum that a large fraction of the light, in particular most of the broad phosphor emission peak 213, is generated far from the central transmission wavelengths of the filters 241, 243, 245 (indicated by the shaded rectangles). A large fraction of the light is blocked by the filters and/or does not contribute to the perceived resolution of a screen equipped with the lighting device.

[0051] FIG. 3 shows a spectral distribution 100 of a screen or lighting device according to an embodiment of the invention. The displayed spectral distribution 100 corresponds to the intrinsic emission from the lighting device. The peaks 113, 115, 117 of the first, second and third light sources each emit a narrow, substantially symmetric peak corresponding to the wavelengths of 625, 530 and 450 nm, respectively. In this case the light sources are LEDs. The narrow peaks 113, 115, 117 ensure that substantially all light can be used to form the coloured screen emission and hardly any light is to be filtered out. In particular the peak 113 of the first light source is narrow, with a FWHM of about 14 nm.

[0052] The illustrated spectral distribution 100 enables the screen to emit white light when desired, with a CCT (correlated colour temperature) of about 6500 K, corresponding to natural daylight.

[0053] FIG. 4A shows a spectral distribution 400 emitted by a screen or lighting device according to an alternative embodiment of the invention. The spectral distribution 400 comprises peaks 413, 415, 417, corresponding to first, second and third light sources, respectively. In this case, the light sources are VCSELs. The first light source emits a peak 413 around 625 nm, the second light source emits a peak 415 around 525 nm, and the third light source emits a peak 417 around 450 nm. The bandwidths (FWHM) of the three peaks are about 5 nm or less.

[0054] FIG. 4B shows a colour space or gamut 401 corresponding to the spectral distribution in FIG. 4A. It can be appreciated that the colour space 401 of the spectral distribution emitted by the claimed device (labelled SPD) is larger than the colour space 409 according to the HDTV (rec. 709) standard or the colour space 408 according to the UHDTV (rec. 2020) standard, due to the wavelength of the second peak 415, which is shorter than the corresponding peak in the standards (about 535 nm). Therefore, more different colours can be generated with a lighting device emitting light with the SPD spectral distribution, compared to those emitting light according to the standards.

[0055] FIG. 5 shows the spectral distribution 400 of FIG. 4A, with the characteristic transmission spectra 443, 445, 447 of the filters corresponding to the respective peaks 413, 415, 417. The transmission spectra 443, 445, 447 have very limited or substantially no overlap with the peaks 413, 415, 417 of the light sources and are distant from the 555 nm range.

[0056] The invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

[0057] Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.