Modeling Sources in LightTools

http://www.cadfamily.com/downinfo/303169.html

It is important to consider the electrode structure of the LED to produce accurate models.The electrode usually blocks the light emitted from the die,which can produce distinct patterns in the output beam.This is a critical consideration for applications where uniform illumination is needed. Most LED designs use a single circular electrode at the top. Many other electrode configurations exist, primarily to provide more uniform current densities.Uniform current density is important to obtain uniform luminance.Current-spreading layers are common in LEDs to produce uniform current density across the die.AlGaInP,AlGaAs,SiC,GaAsP,and GaP die(s)typically have one contact on the top and one on the bottom of the die.
The GaN/Al2O3 die typically has both contacts on the top.Figure 49 illustrates schematics of various electrode structures found in LEDs.