An investigation into LED multiplexing and homogenisation

Currently the market for white light emitting diodes (LED) is dominated by the use of blue pump LEDs and a photoluminesant material which combine to make a white light. An alternative approach is multiplexing where different coloured LEDs (usually red, blue and green) are mixed to produce white light. The advantages of this approach are there is no longer a dependency of the photoluminesant material, the brightness and efficiency is now only subject to how well the LEDs and optical system work. There is also the advantage of being able with the correct combination of wavelengths to reach almost all parts of the CIE chromaticity diagram which would allow a multitude of correlated colour temperatures (CCT). This paper will investigate the use of Zemax optical modelling software to create a model of the patent pending Neolight LED Multiplexer, which is designed for LED multiplexing through the use of dichroics. The model will be used to look at the properties of the light exiting the system including a measure of the total luminous flux, the angular distribution, uniformity of the illuminance and colour mixing at the exit aperture. Optimisation is then carried out to find the CCT of the D65 CIE standard illuminant and analysis carried out to determine the changes that creates.