Ceiling Downlight Halogen Lamps
Dichroic or Aluminium?
The Video
Dichroic
Lamps with a dichoric reflector project most of the heat through the back of the lamp. These are intended for use in display fittings, where objects are illuminated by lamps located a short distance away.
In this situation, heat is not projected forward to avoid the illuminated item being damaged. The lamp is installed in a open back fitting, so the heat can be dissipated.
If used in a ceiling downlight fitting, particularly those which are 'fire rated' or of the enclosed type, the excessive heat will damage the lampholder and wiring. It could even cause a fire.
Dichroics are sometimes sold as 'cool beam' lamps.
Aluminium
Lamps with aluminium reflectors project most of the heat forwards with the light. These are the correct type to use in ceiling downlights, as the heat emitted from the back of the lamp is minimised.
The extra heat in the beam from the front of the lamp is not an issue, since objects will not be placed close to the front of the lamp.
Aluminium reflectors are sometimes sold as 'cool fit' or PAR lamps.
Identification
While the packaging should state the type of reflector, the lamps themselves often are not marked. Some retailers, particularly online websites, describe lamps incorrectly. In some cases, the exact type of reflector is not stated at all.
An easy way to identify
By placing a light source behind the lamp, or holding the lamp up to a window, the type of reflector is easily identified.
Dichroic reflectors will appear partially transparent, usually with a pink or orange tint.
Aluminium reflectors are solid, and no light will pass through them.
Summary
Dichroic reflector lamps are fine when used for their intended purpose of display spotlights in open fittings. They are totally unsuitable for room lighting and should not be used. They are a fire hazard when used in enclosed light fittings.
When purchasing lamps for downlights or other general illumination, ensure that they have aluminium reflectors.
