Extractor Pattern Design for 3D Textured Displays and Light Pipes

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1、Click to edit Master text styles,,Second level,,Third level,,Fourth level,,Click to edit Master title style,,Backlight Optimization,LT Seminar, Novi, June 2005,32,Extractor Pattern Design for 3D Textured Displays and Light Pipes,Dr. William J. Cassarly,,Optical Research Associates,,billc@,,,,Abstra

2、ct:,,The design of backlit displays and light guides used in instrument lighting often includes the use of 3D textures on the flat surfaces of a complicated plastic part. This talk will describe an iterative technique that can automatically define the texture pattern for a desired spatial luminance

3、 distribution by using illumination simulation results. Numerous examples using LEDs and CCFLs will be demonstrated.,,Outline,,Display devices,,Backlights,,Instrument Panels,,Appliqué,,Optimization,,Elements of an optimizer,,Merit Function and Noise,,Mesh Feedback Optimization,,Examples,,Variable s

4、ize and placement,,1D (CCFL) and 2D (LED),,Summary,,What Is A Backlight?,Backlights,,LCD backlight,,Instrument Panels,,Appliqués,,etc,,Nominally Consists of,,A light guide,,Usually made of plastic,,A light source,,CCFL and LED are typical,,Optic to increase collection efficiency,,Other elements ofte

5、n used,,Diffuser,,Brightness enhancing films,,Backplane reflector,,Some elements may not be used, depending on size, cost, and other requirements,Typical Backlight,Light source,Light guide,Diffuser + BEF,Reflector,Reflector,Typical Design Goal,Extract light in a direction perpendicular to the direct

6、ion of propagation,,Spatial light modulator (e.g., LCD or Appliqué) is placed over the backlight,,Typically want uniform light extraction,Light Source,Preferred direction of light extraction,Direction of light propagation,Light Guide,Light extraction from a light guide,Design Process: Uniformity,Ava

7、ilable power varies within the light guide,,Extraction efficiency,varies along length to compensate,,Ways to vary extraction efficiency include,,Paint density, Texture size, Texture spacing,,Need a means to design the extraction pattern,Distance from the source,Available power,Extraction efficiency,

8、Uniform output,Optimization,,Optimization,,Ability to automatically refine the performance of a system based upon a user specified performance criteria,,Parameterization,,Definition of system variables,,Choose variables that influence performance,,Merit Function,,Quantifies system performance,,Small

9、er value means better performance,,Algorithm,,Various possible methods,,Local versus global,Optimization,,Algorithm,Merit,,Function,Model,,Parameterization,User Interface ties these elements together,Optimization Flowchart,,,,,Evaluate Merit Function,,,,Compare MF With Termination Criteria,Setup,Alg

10、orithm Computes New Variable Values,Update Model,Done,Merit Function,,Optimizer needs quantity to determine ‘goodness’,,Called the Merit Function, MF,,Weighted Sum of the Squares is typical,,Smallest MF when V,i,= T,i,for all i,,Weights, W,i,, control relative importance of the V,i,- T,i,MF =, W,i,

11、2,(V,i,- T,i,),2,,,W,i,= Weight of i,th,MF item,,V,i,= Current Value of i,th,MF item,,T,i,= Target of i,th,MF item,,Termination,,V,i,can be obtained using Monte Carlo simulations,,Values have noise,,,i,,,and therefore the Merit Function has noise,,LightTools,®,computes the noise in the Merit Functi

12、on,,Typically, reduce noise by tracing more rays,,Optimizer terminates when Noise becomes large relative to MF,Luminance,,with,,10,000 Rays,Luminance,,with,,1,000,000 Rays,MF =, W,i,2,(V,i,+ ,i,- T,i,),2,,,MF =  W,i,2,(V,i,- T,i,),2 +,Noise,Feedback Optimization,,Most backlights represent a very

13、special type of illumination system,,There is a 1:1,correlation,between the extractor position and the spatial luminance distribution,,Properties of paint or 3D texture extractor elements (size, depth, position, etc.) affect the luminance distribution in a relatively localized manner,,An efficient o

14、ptimization algorithm is possible because of this correlation,,This approach is very powerful and will be described over the next few slides,Mesh Feedback Optimization,,Uniformity obtained by iteratively changing the paint or texture pattern,,Reduce extraction where (il)luminance is too high,,Increa

15、se extraction where (il)luminance is too low,,Amazingly robust,,STARTING PATTERN CAN BE ‘FAR’ FROM FINAL PATTERN,Evaluate (il)Luminance,Adjust Extraction Pattern,Uniformity OK?,NO,YES,Examples,,Changing Size,,3D texture placement does not change, but extraction efficiency depends upon feature size,,

16、Paint density (size of paint dot),,Prism Width/Depth,,Sphere or Cone Tip Depth,,Changing Placement,,Feature size stays constant, but extraction efficiency depends upon relative spacing,,Typically chosen to avoid step of ‘painting’ the backlight by integrating placement features into the mold,,Exampl

17、e 1, CCFL with Painted LP,,6 merit function evaluations to obtain reasonable solution for 2D texture pattern with uniform grid at start,Small Source,,(e.g., LED),2D Display,Texture Pattern,Output,Example 2, LED with Painted LP,,Single 120° LED, air space between LED and light pipe,,Max density near

18、the input (left) edge,,Start,Final,Example 3, LED with Painted LP and Cutout,,Single LED with circular cutout near the input,,Max density near the far (right) edge,,Circular cutout,Start,Final,Example 4: Prism Width Example,,Lambertian LED located along left edge of backlight,,Surface composed of

19、+/-45° prisms with the width variable. Prisms are rotated 45° with respect to the backlight edges.,,Resulting prism width distribution is very non-uniform, but output is uniform,,,Prism Width Distribution,,Start,Final,Texture Pattern,Output,Example 5: Sphere Depth,,Lambertian LED located along lef

20、t edge of back light,,Surface composed of equally spaced spheres with constant radius,,No paint applied to the texture,,Surface to vertex of sphere is varied,,Surface to Vertex,Surface to Vertex Distribution,Final Luminance,Example 6, Paint Density with NonUniform Target,,This example illustrates a

21、 target distribution,,that is not constant.,,The letters L and T have target values that are twice the background.,Texture Pattern,Output,Start,Final,3D Textures, Placement,,Changing 3D texture spacing is more complicated than changing feature size,,,Typically need to avoid overlap of 3D textures,,S

22、pacing changes in one region can alter spacing in another,,Total number of 3D textures can change,,2D extraction pattern is more complicated than 1D,Prism,Spacing,with CCFL,Polynomial prism spacing coefficients controlled,Prism Spacing, After,Prism Spacing, Before,Optimize with 5000 ray, Results sho

23、wn below with 50,000 rays,Specify 2D Density,,Zone is divided into Nx by Ny bins,,Area = BinArea,,Bins contain 3D textures,,Number = N,ij,,3D textures fit inside rectangles,,Rectangle Area = A,,Density,ij,= N,ij,(A/BinArea),,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

24、,,,,,,,,,,,,,,,,,,,,,,,,,2D Placement,,2D spacing is defined using 2D mesh.,,Within each bin of the mesh, spacing is either,,uniform in X and Y, or,,neighboring bins are used to compute a slope term and the spacing is varied linearly across a bin.,,Number of bins equals number of mesh bins, by defau

25、lt, but user can over-ride,,,2X2,4X4,4X4 with linear change,Dither Within a Bin,,Dither allows textures to have ‘random’ shifts with respect to their nominal centers, but randomization is controlled so that textures do not overlap,Dither X,Y=1,0,Dither X,Y=0,1,Dither X,Y=1,1,Dither X,Y=0,0,Dither X,

26、Y=.2,.2,Dither X,Y=.5,.5,Placement with Hemisphere Textures,,Nonuniform placement of identical textures is used to vary the extraction efficiency,,This example uses ‘smooth’ hemisphere textures (i.e., no diffuse paint on the textures),Texture Density,Output,LED,Start,Final,Two LEDs, No Symmetry,,Pla

27、cement example,,Two LEDs,,No symmetry,LEDs,Start,Final,Texture Density,Output,Texture Density,Output,Two LEDs, Some Symmetry,,Placement example,,Two LEDs,,Some symmetry,,Texture Density,Output,LEDs,Start,Final,Texture Density,Output,Zero Target Edge Bins,,It is not always desired to have the edge re

28、gion of the light pipe lit,,By using zero targets around the edge, uniform output within the center region is obtained,,Notice that optimization increases density near edges of the target,Texture Density,Output,LED,Zero target edge bins,Texture Density,Output,Start,Final,Nonrectangular Shape Example

29、,,A new feature in LT computes area of partial bins areas on a surface,,This example uses the partial areas as the optimization targets,,Texture Density,Output,LED,Cutouts,Matching Target,partial edge bins,Texture Density,Output,Start,Final,Prismatic Films,,Prismatic films are often added to a backl

30、ight,,increase on-axis luminance,,reduce off-axis luminance,,LED,Backplane,Light Pipe,Prism Films,Texture Density,Output,Start,Final,Texture Density,Output,Low and High Contrast Targets,,Nonuniform targets can have spatial structure and can have variable contrast,,Shown here are 0:1 and 0.5:1.0 exam

31、ples,TARGET,DENSITY,ILLUMINANCE,TARGET,DENSITY,ILLUMINANCE,LOW,,CONTRAST,,TARGET,HIGH,,CONTRAST,,TARGET,Hybrid Optimization,,Helps to decouple efficiency and uniformity,Done,Evaluate Illuminance,Adjust Extraction Pattern,Uniformity OK?,Evaluate Merit Function,Compare MF With Termination Criteria,Set

32、up,Algorithm Computes New Variable Values,Update Model,Summary,,An overview of backlights and optimization was provided,,Statistical noise impacts the optimization algorithm,,Termination criteria,,Mesh Feedback Optimization Described,,Changing extractor sizes,,Changing extractor placement,,Lots of examples,,ROBUST and FLEXIBLE!!!,,