Version 6.0 of the LightTools illumination design and analysis software package, scheduled to ship in Summer 2007, includes features that will enhance the capabilities of any optical designer.

LightTools 6.0 includes a major enhancement that allows optical designers to create models with multiple levels of immersion. Now a geometric solid A can be surrounded by, or immersed in, solid B, which is in turn immersed in solid C. This feature is especially useful for designers that need an accurate light-emitting diode (LED) model. A white LED model will have the blue-emitting die immersed in a phosphorescent material, which itself is immersed in the epoxy dome. A designer can also add another level of detail by modelling the LED die as a volumetric emitter immersed in a cube of gallium nitride. Using an apodised volume emitter as the diode junction provides the highest model accuracy.

Often, one piece of geometry is not fully immersed inside another. The traditional software solution for partial immersion forces the designer to break one solid into two or more parts so that each piece is fully immersed in its proper material. LightTools allows partial immersion without the need to split the geometry, even when an object has multiple levels of immersion.

This release of LightTools also marks the end of the Beta period for its fully integrated illumination optimisation engine. During the Beta, the optimisation engine was successfully used in many illumination designs worldwide, ranging from LED optics to LCD backlights to helmet mounted displays.

In many systems, there is a tradeoff between uniformity and efficiency; increasing one reduces the other. A new optimisation enhancement balances this tradeoff and assists in finding a design that best meets both conditions. One system that benefits from this enhancement is an LCD backlight, in which the output needs to be very uniform and have minimal losses.

Parameter sensitivity

LightTools 6.0 marks the first availability of the Parameter Sensitivity utility, which allows an engineer to analyse the effect on the performance of a design by small changes in model parameters. The utility is available in conjunction with the optimiser; the parameters and metrics used by the Parameter Sensitivity utility are the same variables and merit functions used by the optimiser. Hence, any model parameters that can be used as optimisation variables can be utility parameters; these parameters can range from surface curvatures to the distance between optical elements. Individual surface reflectivities or scatter profiles can also be used as parameters. The performance metric used by the utility is any analysis metric that can be used as a merit function. Uniformity, efficiency, and level of collimation are just a few of the possible metrics.

For each parameter defined for the Parameter Sensitivity utility, a minimum, maximum, and number of steps are established. The utility evaluates the performance metrics at each of the combination of steps for the parameters and reports on the changes that occur at each permutation. Upon completion of the analysis, the user is presented with curves that show the performance metric as a function of the individual parameters. This information allows the designer to establish sensitivities for the parameters.

Comparing these sensitivities to manufacturing tolerances determines whether or not a design can be manufactured while maintaining a performance specification.

Enter 24 or at www.engineerlive.com/eee

Michael Zollers is Senior Optical Engineer, Optical Research Associates, Pasadena, California, USA. www.opticalres.com