Ceramic discharge metal halide lamp
Encyclopedia
The ceramic discharge metal-halide (CDM) lamp, mostly referred to as Ceramic Metal Halide lamp (CMH), is a relatively new source of light that is a variation of the old (high-pressure) mercury-vapour lamp. The discharge is contained in a ceramic tube. During operation, the temperature of this ceramic tube can exceed 1200 kelvin
s. The ceramic tube is filled with mercury
, argon
and metal-halide salt
s. Because of the high wall temperature, the metal halide salts are partly vaporized. Inside the hot plasma
, these salts are dissociated into metallic atoms and iodine.
The metallic atoms are the main source of light in these lamps, creating a bluish light that is close to daylight with a CRI (color rendering index) of up to 96. The exact correlated color temperature and CRI depend on the specific mixture of metal halide salts. There are also warm-white CDM lamps, with somewhat lower CRI (78-82) which still give a more clear and natural-looking light than the old mercury-vapour and sodium-vapour lamps when used as street lights, besides being more economical to use.
CDM lamps use one fifth of the power of comparable tungsten
incandescent light bulb
s for the same light output (80–117 lm/W) and retain colour stability better than most other gas discharge lamps.
Applications for these lamps include television and film making as well as shop lighting, digital photography
, street and architectural lighting
.
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s. The ceramic tube is filled with mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
, argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
and metal-halide salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
s. Because of the high wall temperature, the metal halide salts are partly vaporized. Inside the hot plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
, these salts are dissociated into metallic atoms and iodine.
The metallic atoms are the main source of light in these lamps, creating a bluish light that is close to daylight with a CRI (color rendering index) of up to 96. The exact correlated color temperature and CRI depend on the specific mixture of metal halide salts. There are also warm-white CDM lamps, with somewhat lower CRI (78-82) which still give a more clear and natural-looking light than the old mercury-vapour and sodium-vapour lamps when used as street lights, besides being more economical to use.
CDM lamps use one fifth of the power of comparable tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
incandescent light bulb
Incandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...
s for the same light output (80–117 lm/W) and retain colour stability better than most other gas discharge lamps.
Applications for these lamps include television and film making as well as shop lighting, digital photography
Digital photography
Digital photography is a form of photography that uses an array of light sensitive sensors to capture the image focused by the lens, as opposed to an exposure on light sensitive film...
, street and architectural lighting
Lighting
Lighting or illumination is the deliberate application of light to achieve some practical or aesthetic effect. Lighting includes the use of both artificial light sources such as lamps and light fixtures, as well as natural illumination by capturing daylight...
.