The bright form of lighting used in stadiums, road ways and in some luxury cars must have caught your eye. If you are curious enough to go near them, you might have noticed that they also emit low heat and much more light compared to normal incandescent or fluorescent lights. To produce that bright light, a technology referred to as high intensity discharge (HID) is used.
What is high intensity discharge (HID) lighting?
HID produces light using an electric arc made of transparent/translucent fused quartz or fused alumina arc tube, gas and mineral salts, and electrodes usually tungsten. This greatly differs from traditional lighting where a wire filament engulfed by an inert gas is used.
What is an electric arc?
Also known as voltaic arc, electric arc was discovered in 1802 by a Russian scientist Vasily V. Petrov. An electric arc is described as current flow from one electrode to another through a non-conductive element such as air or other gases.
How high intensity discharge lighting works
Depending on their intended use, color rendering index (CRI), color temperature (K), energy efficiency, lifespan and light intensity required, different gases and minerals are used to produce high intensity discharge lighting.
Using the arc theorem, a gas is used to initiate the arc (current flow from one electrode to another through a non-conductive element). The arc then heats the metal salts to evaporation resulting to formation of plasma. The plasma amplifies the light intensity from the arc while reducing power consumption. A similar technology that relies on formation of plasma through voltage, noble gases and mercury is plasma displays.
According to the attained color temperature measured in Kelvin (K), HID lighting can produce 4100K (similar to sunlight) or go as high as 8000K producing an elegant blue hue light mostly used in luxury cars. Mercury is used to produce the bluish-greenish light; while Xenon, metal and ceramic metal halides produce a more natural light when at 4100K. Under a low pressure, sodium gives a deep yellow-orange light commonly used in dark rooms.
Uses of high intensity discharge lighting
HID lighting is used to provide high intensity lighting and low power consumption. Today the technology is used and not limited to, car headlights, stadiums, swimming pools, movie theatres, and parking lots. Since HID lighting can match natural light, it can also be used in indoor aquariums and gardens.
Caution
Most HID lamps produce UV radiation and care should be taken when purchasing them. It is recommended that you use HID lights fitted with UV-blocking filters.
Sources:
Howstuffworks – How do the blue-ish headlights on expensive luxury cars work?
Orca.st.usm.edu – HID Headlight FAQ and Installation [What is meant by color temperature?]
Danielsternlighting.com – Thinking of converting to HID?
Ausport.gov.au – High intensity discharge lamps (pdf) [pg3 – Types of Lamps]
