Fluorescent Lamps and Incandescent Lamps
Fluorescent lamps operate by passing electrical current through a gas or vapour contained in glass bulb, which is in turn coated with phosphor on the inside. The electrical discharge created within the vapor (often mercury vapor) is transformed into light energy by passage through the phosphor coating. Such lamps are efficient, in that a good proportion of the discharge engery is turned into light, and modern developments which use a triple coating of phosphor have allowed these lamps to give much better colour rendering. Fluorescent lamps also have a long life.
The range of compact fluorescent lamps offers the performance and life of conventional fluorescents, with the added advantage of a small lamp size. They are increasingly popular in many design applications, and a wide range of fitting is now available for them. Miniature fluorescents allow excellent lighting from a lamp little bigger than a pencil.
Standard fluorescent lamps require ballast and a starter gear; today electronic high frequency ballasts should be used for preference, since these both avoid problems of flicker on start-up, and allow the lamps to be dimmed.
In contrast, incandescent lamps generate light by the passage of an electric current through a wire coil mounted in a vacuum. These were the earliest type of lamps to be developed, and are still widely available, particularly for domestic use. They are, however, relatively inefficient, much of the energy used being radiated as heat rather than light, and the lamp life is relatively short. The first major development in incandescent lamps was the tungsten GLS lamp, which has a warm colour, followed by PAR lamp, with its integral reflector, which allows better directional control. PAR lamps also a longer lamp life.
Tungsten halogen lamps have a light quality that is closer to daylight than standard or tungsten incandescent, as well as longer lamp life. Developments in mains-voltage tungsten halogen allow these lamps to be retrofitted into existing main systems.
Lower voltage tungsten lamps offer excellent colour rendition, small lamp sizes, long life and low operating costs. However, these lamps require transformers which are either integral to the fitting or need to be mounted near the lamp.