 The Source Four's reflector is dichroic, meaning that it reflects light of only certain wavelengths.The Source Four's reflector reflects back 95% of the visible light striking it, while allowing over 90% of the infrared radiation (heat) to pass out the back of the instrument.This produces a much cooler light which is less destructive to gobos or color gels at the front of the fixture, and reduces localized heating of the lighting target.