Halogen Lighting – A Guide For The Domestic Buyer

The Halogen Cycle

The process by which Halogen lamps actually work! Occurring when the filament of a Halogen lamp has reached operating temperature, Halogen atoms within the bulb envelope attach themselves to the vaporised Tungsten particles emanating from the filament. The Halogen atoms carry them back to the filament where they are reused.

Linear Tungsten Halogen Tube

The high wattage tubular lamps found in security floodlights. These were among the first commonly used domestic halogen lamps, and whilst they now come in lots of different sizes, wattages and voltages, by far the most common is still 117mm, 300w or 500w, 240v. They have two ceramic caps at each end, and must not be touched by the bare hands when installing, as the salt from the sweat of your fingers will compromise the quartz envelope at high temperatures, leading to explosion!

Dichroic Lamp / ‘M’ Lamp

This very popular Halogen Reflector is the lamp principally seen in recessed down lights. The word ‘dichroic’ refers to the fact that electromagnetic radiation is split into two distinct areas: heat and visible light. A dichroic filter throws light forward and two thirds of the heat backwards through the reflector. Whilst the term ‘dichroic’ relates to both mains and low voltage lamps, it is commonly used when referring to low voltage ‘m’ lamps.

The two common sizes are 50mm and 35mm. This measurement describes the diameter of the reflector. Dichroic lamps are available in many wattages, and with a range of beam widths, covering both ‘spot’ and ‘flood’ applications.

Most lighting manufacturers and some in the lighting trade still abide by the original naming convention which used ‘M’ numbers. A 50mm, 50w, 38degree for example is an M258, whilst an M223 is 35mm, 35w, 38degree.

In terms of its cap the Dichroic lamp follows a low voltage standard in having two parallel pins at its base which fit into a ceramic lampholder.

Coming in a variety of colours, they are nowadays, usually glass fronted, to prevent the touching of the sensitive quartz capsule.

GU10 Halogen Lamp

The mains version of the 50mm dichroic. These lamps were developed fairly recently in response to the need for a compact halogen lamp for use without a transformer. GU10s are distinct physically from their low voltage counterparts by their base or cap. GU10s have a large bevelled ceramic base with two thick ‘twist and lock’ studs which fit into a plastic lampholder. (Dichroics, as described above, have two parallel pins).

GZ10 Halogen Lamp

Similar to a GU10 lamp, in that it is a mains halogen lamp. Unlike a GU10, however, which has an aluminium reflector, GZs use a dichroic reflector so that all the heat produced during normal operation is thrown backward. GZ10s are used in applications where heat must not be thrown forward.

Par Lamp

Halogen version of the common incandescent reflector. These too were developed fairly recently and met demand for a halogen lamp which fitted existing fittings. They therefor, most commonly, have an ES cap, though SES and BC versions are available. Their physical size is part dependent upon the wattage, which can range from 25w – 150w. A typical spec would be Par20, 50w es.


Original brand name for par lamps and GU10s coined by Sylvania, the first company to bring mains halogen lamps to the market.

Capsule Lamps

Very small 2 pin low voltage lamp. They are available in a range of wattages and in two different cap sizes, either G4 or G6.35. This measurement refers to the 4mm or 6.35mm distance between the two pins.


Rather like a capsule lamp but operates on mains not low voltage. They may be distinguished from a capsule lamp as they slightly larger and have 2 ‘loops’ rather than 2 pins at the base. G9 refers to the 9mm gap between these two loops. 25w, 40w, 60w, 75w, frosted or clear.


Like a G9, Halolux lamps are used in a mains voltage environment, but are fitted with standard SBC, SES or ES caps instead of two loops. With a second envelope housing the ‘working’ capsule they are physically bigger than a G9. Made only by Osram, they are available in frosted or clear.


Like a Halolux, Halogenas employ two envelopes and standard caps, this time BC and ES. Made only by Philips they are available in 100w and 150w.

For more information on all mains and low voltage halogen lighting please visit Gil-Lec