文稿案例成果lcd example

1、Lighting & Illumination Design Using ZEMAXLCD Backlight3 - 2 LCDLiquid crystal displays (LCDs) are one of the most commonly used display technologies in the marketBottom-lit designs use sources placed behind the LCDEdge-lit designs use a wedged guide to distribute light from a source placed beside t

2、he LCDA brightness enhancement film (BEF) is used to control the intensity and polarization of the emitted lightWe will use ZEMAX to model the BEF using an array of prismsCan use the Array object to model the array with a small memory footprint3 - 3 Schematic of LCD BacklightSource is usually a cold

3、-cathode fluorescent lamp (CCFL) or a series of light-emitting diodes (LEDs)Place a reflector behind the source to increase system efficiency3 - 4 LCD Backlight Design SpecsConstraints used in our design:Display area based on a standard cell phone75 mm x 75 mmLight guide thickness chosen to limit ov

4、erall package height4 mm input face, 1 mm end faceBEF scaled from VikuitiTM T-BEF 90/24 designSee the Knowledge Base article entitled “How To Model Brightness Enhancement Film” for details3 - 5 LCD Backlight Initial DesignOpen the file SamplesShort coursesc_lcd_backlight1.ZMXFile represents initial

5、setup of LCD backlightSource Tube used to model CCFL sourceCylinder Volume object used to model physical sourceAllows rays to interact with source housingBiconic Surface acts as a cylindrical reflector for the sourceWedged light guide modeled with the Rectangular Volume objectWedge formed using diff

6、erent Y half-widths for front vs. backObject is tilted to ensure upper face of the guide is parallel to the XZ planeFront and Rear faces of the volume are tilted by the same amount to ensure they remain parallel to the YZ plane3 - 6 LCD Backlight Initial DesignRectangular mirrors are placed around t

7、he light guide keep light from leaking out the bottom or sidesSimple Rectangular Volume object is used to model the backing of the BEFEach element in the BEF is also modeled with a Rectangular Volume objectForm triangular prism by setting Back Y width = 0:3 - 7 BEF DesignThe BEF is constructed from

8、an array of triangular prismsPrism half-width = 12 micronsReplicating the parent prism by hand would be time-consumingMore importantly, would slow down ray-tracing significantly!Can create a rectangular array using the Array object:3 - 8 Array ObjectThe Array object allows you to form a rectangular

9、array from any previously-defined object in the NSCESpecify number of elements in X, Y and ZSpecify spacing between elements in X, Y and ZSpacing can be non-linear (up to 4th order polynomial)Grid on which array is formed need not be identical to XYZ axes for local or global coordinate systemDirecti

10、on cosines for each grid axis can be independently specifiedAll object properties are copied, except for “Do Not Draw” and “Rays Ignore This Object”Changes to parent object affect Array, so it can be optimizedUses only as much memory as the single parent object!3 - 9 BEF DesignThe BEF in our backlig

11、ht design is composed of a 3125 x 3125 array of prisms in X and YArray spacing is 24 microns (so that elements just touch)We select “Rays Ignore This Object” and “Do Not Draw” for the parent, so that the parent does not interfere with the ArrayJust like with the Boolean object 3 - 10 Performance Goa

12、lsThe criteria we will use to assess performance of the backlight are:High energy efficiencyCharacterized by the ratio of energy emitted by display to energy emitted by sourceSpatial uniformityMinimum flux per pixel deviationAngular uniformityFor this application (cell phone display), well look with

13、in a small ( 30 degree) half-cone angleFor larger devices (e.g. TV or computer monitor), uniformity would be required over larger angles ( 90 degrees)3 - 11 Initial PerformanceTrace rays with splitting on and errors ignoredAbout 60% of the source energy reaches the detectorSmall amount of energy los

14、t due to ray errorsNegligible for this applicationWill discuss geometry errors in a little bitAlmost 15% of energy lost due to thresholdsTermination criterion for rays is set fairly high Minimum Relative Ray Intensity = 0.001If we lower this to 1.0E-6, energy lost to thresholds is reduced by an orde

15、r of magnitudeRay tracing time increasesTrade-off is up to the engineer!3 - 12 Initial PerformanceInitial illuminance is highest on the side opposite the sourceDue to light guide causing TIR close to the sourceIntensity distribution shows many “hot spots”3 - 13 Add ScatteringApply a Lambertian scatt

16、ering distribution (Scatter Fraction = 1, Number of Rays = 1) to Face 1 of light guide (object #6)Spatial uniformity improves, but not angular performanceMake sure to select “Scatter Rays” during ray-trace3 - 14 Scatter From Top of Light GuideScattering may be more effective elsewhere on the light g

17、uideTry scattering from the top of the guideWith the Rectangular Volume object the top and bottom faces are a single coat/scatter groupCould replace Rectangular Volume object with an object in which top and bottom faces are separateOr add a Rectangular Volume object that overlaps the top of the ligh

18、t guide, and place scattering distribution on that objectAs long as this new object comes AFTER the light guide in the NSCE, nesting rule will apply3 - 15 Scattering ObjectAdd an object in the NSCE after the light guideObject #7: Rectangular VolumeX = 0; Y = 2; Z = 38.5Tilt About X = -90Front/Back X

19、, Y Half Widths = 37.5Z Length = 0.01Face 1: Lambertian scatteringScatter Fraction = 1Number of Rays = 13 - 16 Better Angular UniformityAngular distribution “hot spots” are eliminatedSpatial uniformity is degradedIf scattering is also applied to the bottom of light guide, efficiency is reduced3 - 17

20、 More Effective ScatteringResults suggest ideal scattering profile would be at the top of the light guide and would scatter more light as we move away from the sourceRather than scattering from a rough surface, scatter from an array of non-linearly spaced microstructuresModel using Array objectParen

21、t object will be small spheres3 - 18 Add Array of SpheresDelete object #7 from the NSCE, and add the following objects after the “End Reflector” (which should be object #10):Object #11: SphereX = 37; Y = 2, Z = 75.5Tilt About X = 90Tilt About Z = 180Radius = 0.5Is Volume? = 1Set “Do Not Draw” and “R

22、ays Ignore This Object”3 - 19 Add Array of SpheresObject #12: ArrayRef Object = -1 (relative referencing)Parent Object # = 11Number X = 75Number Y = 59Delta1 X = 1Delta 1 Y = 1Delta2 Y = 0.005 (non-linear spacing)Array only needs to be non-linear in Y due to symmetry of systemDraw Limit = 25 (so arr

23、ay wont be drawn on layout)3 - 20 Optimization Merit FunctionWill optimize array parameters to achieve best spatial and angular uniformityMerit function will look like this:3 - 21 Optimization Merit FunctionIn the merit function:Operands 6 and 9 are used to maximize spatial uniformity and total flux

24、, respectivelyOperands 11 and 12 control the centroid of the intensity distributionOperand 14 controls the radius of the intensity distributionDont want collimated output, but within a range of 30 degreesOperands 16-19 are boundary constraints for array of spheresPrevent array from ing too small or largeNecessary as optimization has a tendency to produce extreme solutions if unboundedNegative weights act as Lagrangian multipliersForce targets to be met3 - 22 Optimize!Define as variables:Sphere (object #11): RadiusA