Effect of voltage on performance
Tungsten halogen lamps behave in a similar manner to other incandescent lamps when run on a different voltage. However the light output is reported as proportional to V^3, and the luminous efficacy proportional to V^{1.3}.[13] The normal relationship regarding the lifetime is that it is proportional to V^{-14}. For example, a bulb operated at 5% higher than its design voltage would produce about 15% more light, and the luminous efficacy would be about 6.5% higher, but would be expected to have only half the rated life.
Halogen lamps are manufactured with enough halogen to match the rate of tungsten evaporation at their design voltage. Increasing the applied voltage increases the rate of evaporation, so at some point there may be insufficient halogen and the lamp goes black. Over-voltage operation is not generally recommended. With a reduced voltage the evaporation is lower and there may be too much halogen, which can lead to abnormal failure. At much lower voltages, the bulb temperature may be too low to support the halogen cycle, but by this time the evaporation rate is too low for the bulb to blacken significantly. There are many situations where halogen lamps are dimmed successfully. However, lamp life may not be extended as much as predicted. The life span on dimming depends on lamp construction, the halogen additive used and whether dimming is normally expected for this type.
Spectrum
Like all incandescent light bulbs, a halogen lamp produces a continuous spectrum of light, from near ultraviolet to deep into the infrared.[14] Since the lamp filament can operate at a higher temperature than a non-halogen lamp, the spectrum is shifted toward blue, producing light with a higher effective color temperature.
Safety
Halogen lamps get hotter than regular incandescent lamps because the heat is concentrated on a smaller envelope surface, and because the surface is closer to the filament. This high temperature is essential to their operation. Because the halogen lamp operates at very high temperatures, it can pose fire and burn hazards. In Australia, numerous house fires each year are attributed to ceiling-mounted halogen downlights.[15][16] The Western Australia Department of Fire and Emergency Services recommends that home owners consider instead using compact fluorescent lamps or light emitting diode lamps because they produce less heat.[17] Some safety codes now require halogen bulbs to be protected by a grid or grille, especially for high power (1–2 kW) bulbs used in theatre, or by the glass and metal housing of the fixture to prevent ignition of draperies or flammable objects in contact with the lamp.
To reduce unintentional ultraviolet (UV) exposure, and to contain hot bulb fragments in the event of explosive bulb failure, general-purpose lamps usually have a UV-absorbing glass filter over or around the bulb. Alternatively, lamp bulbs may be doped or coated to filter out the UV radiation. With adequate filtering, a halogen lamp exposes users to less UV than a standard incandescent lamp producing the same effective level of illumination without filtering.
Effect of voltage on performance
Tungsten halogen lamps behave in a similar manner to other incandescent lamps when run on a different voltage. However the light output is reported as proportional to V^3, and the luminous efficacy proportional to V^{1.3}.[13] The normal relationship regarding the lifetime is that it is proportional to V^{-14}. For example, a bulb operated at 5% higher than its design voltage would produce about 15% more light, and the luminous efficacy would be about 6.5% higher, but would be expected to have only half the rated life.
Halogen lamps are manufactured with enough halogen to match the rate of tungsten evaporation at their design voltage. Increasing the applied voltage increases the rate of evaporation, so at some point there may be insufficient halogen and the lamp goes black. Over-voltage operation is not generally recommended. With a reduced voltage the evaporation is lower and there may be too much halogen, which can lead to abnormal failure. At much lower voltages, the bulb temperature may be too low to support the halogen cycle, but by this time the evaporation rate is too low for the bulb to blacken significantly. There are many situations where halogen lamps are dimmed successfully. However, lamp life may not be extended as much as predicted. The life span on dimming depends on lamp construction, the halogen additive used and whether dimming is normally expected for this type.
Spectrum
Like all incandescent light bulbs, a halogen lamp produces a continuous spectrum of light, from near ultraviolet to deep into the infrared.[14] Since the lamp filament can operate at a higher temperature than a non-halogen lamp, the spectrum is shifted toward blue, producing light with a higher effective color temperature.
Safety
Halogen lamps get hotter than regular incandescent lamps because the heat is concentrated on a smaller envelope surface, and because the surface is closer to the filament. This high temperature is essential to their operation. Because the halogen lamp operates at very high temperatures, it can pose fire and burn hazards. In Australia, numerous house fires each year are attributed to ceiling-mounted halogen downlights.[15][16] The Western Australia Department of Fire and Emergency Services recommends that home owners consider instead using compact fluorescent lamps or light emitting diode lamps because they produce less heat.[17] Some safety codes now require halogen bulbs to be protected by a grid or grille, especially for high power (1–2 kW) bulbs used in theatre, or by the glass and metal housing of the fixture to prevent ignition of draperies or flammable objects in contact with the lamp.
To reduce unintentional ultraviolet (UV) exposure, and to contain hot bulb fragments in the event of explosive bulb failure, general-purpose lamps usually have a UV-absorbing glass filter over or around the bulb. Alternatively, lamp bulbs may be doped or coated to filter out the UV radiation. With adequate filtering, a halogen lamp exposes users to less UV than a standard incandescent lamp producing the same effective level of illumination without filtering.
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