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The Kelvin color temperature scale ranges from 1000K (amber) to 3000K (yellow) to 5500K (white) to 8000K (blue) to 12000K (purple). HID Lamp Color Temperature Range. HID lamps produce different colors of light primarily through the use of various metal additives in the lamp's arc tube and the physics of the gas discharge process. [11]
The color temperature scale describes only the color of light emitted by a light source, which may actually be at a different (and often much lower) temperature. [ 1 ] [ 2 ] Color temperature has applications in lighting , [ 3 ] photography , [ 4 ] videography , [ 5 ] publishing , [ 6 ] manufacturing , [ 7 ] astrophysics , [ 8 ] and other fields.
Like other gas-discharge lamps such as the very-similar mercury-vapor lamps, metal-halide lamps produce light by ionizing a mixture of gases in an electric arc.In a metal-halide lamp, the compact arc tube contains a mixture of argon or xenon, mercury, and a variety of metal halides, such as sodium iodide and scandium iodide. [7]
A densitometer measures the degree of light passing through or reflected by a subject. [4] A color temperature meter measures the color temperature of an incident illuminant. Two spectral reflectance curves. The object in question reflects light with shorter wavelengths while absorbing those in others, lending it a blue appearance.
Separated columns are often a problem in both alcohol and mercury thermometers, and they can make a temperature reading inaccurate. The precision or resolution of a thermometer is simply to what fraction of a degree it is possible to make a reading. For high temperature work it may only be possible to measure to the nearest 10 °C or more.
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HIDs are still used where CFLs or LEDs can't do the job. Namely operation in wide temperature range (CFLs don't like cold, LEDs don't like hot) or at high brightness levels. They tend to produce 'harsh' light - that is light which is not composed of a continuous spectrum, but have light output concentrated at a few wavelengths.
With HMI bulbs, color temperature varies significantly with lamp age. A new bulb generally will output at a color temperature close to 15,000 K during its first few hours. As the bulb ages, the color temperature reaches its nominal value of around 5600 K or 6000 K. With age, the arc length becomes larger as more of the electrodes burn away.