Calendar

SPIE Optics and Photonics
Booth 301
Aug. 26-30, 2007
San Diego, CA
SPIE website

Introduction to Illumination Design Using LightTools
Oct. 1-3, 2007
Pasadena, California
Click here for more details and to enroll

Advanced Topics in LightTools:  Optimization, COM/API, and Photorealistic Rendering
Oct. 4-5, 2007
Pasadena, California
Click here for more details and to enroll

LEDs 2007
Booth 76
Oct. 24-26, 2007
San Diego, CA
LEDS 2007 website

Optimizing Backlight Patterns in LightTools

Backlit displays are used in many applications such as laptops, digital cameras, cell phones, etc.  The most common backlit displays use one or more light sources located on the edge of a light guide designed to direct the light to the front of the display for viewing.  Illumination design engineers are typically trying to meet display brightness and uniformity requirements, with as few light sources as possible in order to minimize manufacturing costs and power use.  These conflicting requirements can be difficult to achieve, so ORA has developed a new LightTools utility for optimizing the extraction patterns for backlit displays.

The new Backlight Pattern Optimization (BPO) utility is available for download from ORA's customer area of the web, www.oraservice.com, under LightTools Support > Utility and Macro Downloads.   The BPO utility is an enhancement to the LightTools Optimization Module (license required) to provide a fast and accurate way to optimize the extraction pattern for backlit displays.  It can work with any type of source (e.g., CCFL or one or more LEDs) and with any type of 2D or 3D texture supported by LightTools, including user-defined 3D textures.  Texture feature size can be as small as necessary with texture patterns as dense as necessary.  Even highly asymmetric source positions can be used (e.g., a single LED at the corner of the display).

BPO requires a starting system that includes a light guide, 2D or 3D extraction pattern (a uniform pattern can be used to start), one or more sources, a receiver parallel to the extraction surface, and a target illumination pattern defined as an optimization mesh merit function (usually uniform, but any target pattern can be used).  The BPO utility includes features for making sure the setup is valid, for displaying pattern density and illumination patterns, and for controlling unwanted effects such as Moiré effects caused by interference of rectangular extraction patterns.

As an example, the figure below shows the initial illuminance on the receiver for a backlit display with a uniform extraction texture and 2 LED sources (Figure 1), followed by figures of the resulting illuminance (Figure 2) and extraction pattern (Figure 3) after BPO has optimized the placement of the extraction textures.

Figure 1. Two LED source with Uniform Extraction Pattern Initial Illuminance

Figure 2. Illuminance after BPO

Figure 3.  Nonuniform Extraction Pattern after BPO

Included in the BPO utility download on www.oraservice.com is a BPO Utility Users Guide, installation instructions, and several example files.  In addition, a related technical paper from the 2006 IODC meeting, "Optimizing Density Patterns to Achieve Desired Light Extraction for Displays", T.L.R. Davenport and W.J. Cassarly, is available for download under LightTools Support > Technical Papers.  This paper used an early version of the BPO utility and confirms its results with a prototype.