LED backlighting system with closed loop control

• US 20090122533A1
• Filed: 10/24/2008
• Published: 05/14/2009
• Est. Priority Date: 11/08/2007
• Status: Active Grant

• Current Assignee: Innovations in Optics, Inc.
• Original Assignee: Innovations in Optics, Inc.
• Inventors: Brukilacchio, Thomas J.
• Granted Patent: US 8,746,943 B2
• Time in Patent Office: Days
• US Class Current: 362/231
• CPC Class Codes: G02B 6/003 Lens or lenticular sheet or layer
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources
• CPC Class Codes: G02B 6/0073 Light emitting diode [LED]
• CPC Class Codes: G02B 6/0085 Means for removing heat created by the light source from the package heat extraction or cooling elements for semiconductor light sources in general H01L33/64
• CPC Class Codes: G02B 6/009 of the light source in the package G02B6/0021 takes precedence
• CPC Class Codes: G02F 1/133507 Films for enhancing the luminance
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/133628 with cooling means

Abstract

A light emitting diode (LED) based illumination system with particular application to large scale side lighted liquid crystal displays (LCD). The invention uses on board closed loop intensity control in conjunction with red, green and blue (R,G,B) LED die and a hybrid non-imaging optical system to overcome substantial temperature dependence, loss in intensity with time, increased system cost and complexity, and decreased dynamic range. The invention obtains a large color gamut in excess of 110% of the NTSC (National Television System Committee) recommendation. A high performance thermal management design, the use of “chip on board” technology, compact and efficient collection optics, and on board closed loop intensity control increase and maintain luminous performance and decrease cost relative to less efficient RGB LED approaches. One or more line sources can be generated for applications other than in lighting LCD displays.

Claims

1. Illumination apparatus for producing high intensity line sources of uniform intensity and spectral content, said illumination apparatus comprising:

an elongated support member having formed thereon a linear array of regularly spaced LED modules each of which comprises one or more LED emitting areas having a predetermined spectral output that is emitted over a predetermined solid angle;

an elongated collection optic having an array of non-imaging concentrators the individual non-imaging concentrators of which are optically coupled in one-to-one correspondence with said regularly spaced LED modules, each non-imaging concentrator in said array of non-imaging concentrators operating to collect radiation emitted by each of said LED modules and to re-emit substantially all of said collected radiation as a diverging beam having a solid angle smaller than said predetermined solid angle over which radiation is emitted by each of said LED modules where said diverging beam is spatially and spectrally uniform in the near field of said exit aperture and propagates in a direction along an optical axis of said apparatus; and

an elongated converging optical element positioned to receive said diverging beam and converge it in a vertical plane to form a line source of predetermined dimensions.

2. The illumination apparatus of claim 1 wherein said LED emitting areas are selected from the group comprising R,G,B LEDs, Blue LEDs used in conjunction with red and green phosphor, and Blue and Green LEDs used in conjunction with red phosphor.

3. The illumination apparatus of claim 1 wherein said non-imaging concentrators are selected from the group comprising compound parabolic, elliptical, hyperbolic concentrators, straight tapers, and concentrators having curvatures described by higher order polynomial functions.

4. The illumination apparatus of claim 3 wherein said non-imaging concentrators are rectangular in cross section to control the divergence of said diverging beam in vertical and horizontal planes mutually perpendicular to said optical axis.

5. The illumination apparatus of claim 1 said collection optic further includes an elongated mixing section having a single continuous surface for receiving said diverging beams from said non-imaging concentrators, mixing their colors for more spectral and spatial uniformity, and re-emitting them along an exit face thereof for travel to said elongated converging optical element.

6. The illumination apparatus of claim 5 wherein said collection optic further includes an elongated θ

by θ

compound parabolic concentrator section following said mixing section and a second elongated truncated compound parabolic concentrator section following said θ

by θ

compound parabolic concentrator section, said θ

by θ

compound parabolic concentrator section being structured to receive the light emerging from said exit face of said mixing section and direct it into said elongated truncated compound parabolic concentrator section after which the light emerging from said second elongated truncated compound parabolic concentrator section strikes said elongated converging optical element.

7. The illumination apparatus of claim 1 wherein said elongated converging optical element comprises a cylindrical lens.

8. The illumination apparatus of claim 7 wherein said cylindrical lens has at least one aspheric surface.

9. The illumination apparatus of claim 5 wherein said elongated converging optical element comprises a substantially cylindrical off-axis parabolic reflector for directing the output from said collection optic through an angle of substantially ninety degrees.

10. The illumination apparatus of claim 1 further including a planar wedge light guide for receiving light from said line source and propagating it along the length of said planar wedge guide, said planar wedge guide having small optical features on one surface thereof to deflect light upwards out of said wedge guide through an exit face thereof opposite to the surface having said small optical features.

11. The illumination apparatus of claim 10 further including a diffuser positioned opposite said exit face of said planar wedge guide to receive light therefrom to improve its homogeneity and control its angular direction for subsequent use with an LCD display panel.

12. The illumination apparatus of claim 1 further including a heat sink attached to said elongated support member to control the temperature of said illumination apparatus by selectively dissipating heat generated in the process of converting electrical energy to optical power to enhance the quantum efficiency of said apparatus.

13. The illumination apparatus of claim 1 further including a plurality of regularly spaced photodiodes mounted on said support member to monitor the individual output of said LED modules to provide a signal for feedback control of the intensity of light output from said LED modules.

14. The illumination apparatus of claim 6 wherein said collection optic is formed as a single piece of injection molded optical plastic.

16. The illumination apparatus of claim 13 further including at least one electronic controller mounted on said support member to receive said signals and provide feedback control of said LED modules.

15. Illumination apparatus for producing high intensity line sources of uniform intensity and spectral content, said illumination apparatus comprising:

an elongated support member having formed thereon a linear array of regularly spaced LED modules each of which comprises one or more LED emitting areas having a predetermined spectral output that is emitted over a predetermined solid angle;

an elongated cylindrical collection optic comprising a substantially parabolic cylindrical hollow reflector having entrance and exit apertures, said cylindrical collection optic operating by reflection to direct the light from said LED modules incident on said reflector into a desired angle space; and

a cylindrical collimation lens centrally positioned on the axis of said substantially parabolic cylindrical hollow reflector to direct light incident thereto from said LED modules in directions through said exit aperture and within said desired angle space so that substantially all of the light collected by said collection optic is emitted therefrom as a diverging beam having a solid angle smaller than said predetermined solid angle over which radiation is emitted by each of said LED modules where said diverging beam is spatially and spectrally uniform in the near field of said exit aperture and propagates in a direction along an optical axis of said apparatus; and

an elongated converging optical element positioned to receive said diverging beam and converge it in a vertical plane to form a line source of predetermined dimensions.