Downlights and Dichroic bulbs.
Bulbs, namely the MR16 (Low voltage) and GU10 (Mains voltage) with Dichroic reflectors
commonly reflect visible light forward whilst allowing the invisible infrared light (RADIATED
HEAT) to pass out of the rear of the fixture, resulting in a beam of light that is “cooler”.
The integrated dichroic reflector, was originally designed for use in slide projectors to avoid
melting the slides and photographic film, but now widely used for interior home and commercial
lighting with a decorative purple coloured light coming from the rear.
They pose a serious fire hazard if used in recessed downlights or enclosed
luminaires by allowing infrared radiation (HEAT) into those luminaires
Also if the luminaire is a fire rated unit with intumescent seals, they are likely to activate the
seals prematurely and cause the lamps components to melt and drip onto the surface below
For these applications non-cool beam (ALU or Silverback) lamps must be used.
NEVER EVER use a dichroic bulb for a downlight.
They can be easily identified if you hold them up to the light and look through the rear of the
bulb. A dichroic bulb will have a purple or pearly colour, whilst an aluminium reflector bulb will
look dark and silver as it won’t pass any light (or heat) through.
Unfortunately, both types are sold side by side, are totally interchangeable and are still called
MR16 and GU10, but are VERY different, dichroic are usually cheaper and more likely to be
Lamps suitable for use in recessed or enclosed luminaires will have the ALU or aluminium
reflector on the packaging and will have a symbol showing red wavy lines (heat) coming from
the front of the bulb.