Have you ever been out shopping for replacement lamps for your home and saw acronyms like HID, HPS, MSR, and HMI? These acronyms refer to lamps that are different than your typical household incandescent with a filament – HID stands for High Intensity Discharge lamp, and refers to lamps that utilize an electric arc to create light. HID sources are typically very, very bright, and have a very high color temperature on average. Color rendering indexes, and correlated color temperatures are all usually very high in HID sources.
High intensity discharge lamps don’t have a filament, and do not function like an incandescent lamp except for in the fact that they require electricity. As a matter of fact, they’re about twice as efficient than incandescent Tungsten Halogen filamented sources, typically. Once the lamp is ignited, it burns consistently and clean during its arc phase.
Take a look at this image:
HID sources usually consist of a few basic parts – an arc tube, arc electrodes, a metal salt, and a gas, usually of the halogen or chalcogen family on the periodic table. Once the arc is ignited, the gas and metal salts heat and evaporate to a plasma phase, which greatly increases the light output of the lamp, and also makes it use less electricity. HID lamps need a ballast to both start and maintain the arc that occurs in the arc chamber (the glass envelope part of the lamp) – to start, the ballast sends a high voltage across the arc gap, which refers to the distance between the electrodes. Depending on the lamp, this could be as little as 500V or as much as 3500V. Once the arc is established, the ballast drops the voltage down to a “maintenance” voltage, maintaining the arc and keeping the lamp lit.
HID laps are similar to welding – they put off high amounts of very high color temperature light that can hurt your eyes if you look directly at them. HID lamps are sort-of like controlled welding in a way, except the deposit that welders make is not quite how HID lamps operate. HID lamps are made of all sorts of chemistries, from Mercury Vapor lamps (the streetlights that are extremely white/blue), Sodium Vapor lamps (very yellow/amerish light), to Medium-Source Rare-Earth or Hydrargyrum Medium-Arc Iodide lamps.
What? Hydrargyrum? Did someone burp? Hydrargyrum is another name for Mercury.
HID sources are used all over the place. When a need for wide area lighting is required, HIDs do the trick – next time you’re at your favorite big-box retailer, look up and see what’s lighting the store. Fluorescent tubes are HID lamps, and they are found everywhere. HIDs are used in Film and TV Lighting, moving lights, and anywhere that a bright, consistent and efficient source of light is needed. They’re everywhere – the World Trade Center site, atop the Luxor in Vegas, in some car headlamps, video projectors, and in millions of other places.
Handling of HID sources takes some extra care; when changing out an HID source, the best bet is to use some sort of face shield and eye protection while it is still warm. As the lamp cools down, the lamp is even more fragile than in its cooled state, and could possibly explode in your face if you weren’t careful. Never look at the source, as mentioned before – this can cause overall blindness and loss of night vision. HID sources are usually high voltage sources too when in operation. Take extra care!