The Köhler illumination concept was originally invented to achieve uniform illumination in microscopy1. Köhler
integrators can also be formed by arrays of lenticulations that can be any combination of reflective and/or refractive
surfaces, organized in corresponding pairs. Arrays of integrating facets can be arranged not only on flat surfaces but on
rotationally symmetric and even freeform surfaces6. Currently flat lenslet arrays are widely applied as homogenizing
optics2 for lithography, machine vision illumination, and projection.
Adding Köhler facets onto already designed surfaces can improve the optical system performance, while respecting its
original function. In general, the optics output can be made somewhat independent of the source characteristics, although
at the expense of a slight ètendue dilution or efficiency losses.
This work revises the Köhler concept and its application to different kind of optics, ranging from photovoltaic
concentrators to automotive LED headlights. In the former, irradiance peaks on the solar cell can be avoided, while
preserving high aiming tolerance (acceptance) of the solar concentrator. In the latter, LEDs drawbacks like large source
image sizes, source misalignments, ill defined source edges, and low source radiance can be compensated.