Halogens are Incandescent Lamps where the filament envelope is filled with a gas from the Halogen Family (Chlorine, Bromine, Fluorine, Iodine) thus enabling it to produce a larger amount of light and have a significantly longer life, since the halogen enables the tungsten vapour to recondense back on the filament. As a result, halogens are twice as efficient and have twice the lifetime of Incandescent Bulbs.
ADVANTAGES-
·Availability and Cost: They are easily available and do not cost much - Rs50 to Rs 300, depending on the optics, colour and filters.
·Variety: In the dichroic version, they are available in different colour temperatures and beam angles which make them an ideal choice for lighting Art and residential Interiors.
· Colour rendering: They have perfect colour rendering (Ra-100) that causes object colours to appear almost the same as in natural daylight.
· Control: They can be dimmed easily, by simply varying the input voltage.
DISADVANTAGES-
· Luminous Efficacy: The Luminous Efficacy is quite low- at best around 30 lumens per watt.
· Life: The Lifetime is also quite low compared to other lamps - 2000 to 4000 hours. They burn out without warning and need regular replacement.
· Replacement: Replacing a halogen bulb is a very delicate operation. You cannot smudge it with your fingertips because the slight deposit of grease will burn from the too high heat resulting in the speedy loss of the bulb.
· Heat: Halogens are hot and piercingly bright and produce a significant amount of heat in a room.
USAGE:
Since, halogens provide a very even, vibrant light and have perfect colour-rendering, they are used predominantly for warm spotlighting of art and accent lighting. They are also used in automobile headlights, underwater lighting and as outdoor floodlights.
Because of their limited uses and poor efficiency they are not a very popular choice nowadays. More energy efficient options like CFLs are preferred.
