Popular light sources currently used for solar simulation include the Hydrargyrum Quartz Iodide (HQI) lamp which is a type of high-intensity discharge (HID) light, produces its light by an electrical arc in a gas envelope using electrodes. Note that Hydrargyrum is the Latin name for the element mercury. Also Xenon lamps that use tungsten metal electrodes in a glass tube filled with xenon gas. For xenon flash tubes, a third "trigger" electrode usually surrounds the exterior of the arc tube. Xenon lamps often have a relatively short lifetime of 200 to 2000 hours. As with all electrode based light sources the colour quality and luminous efficiency of the light changes dramatically as the electrodes burn away during use. And the tungsten lamp, which is similar to the classic incandescent domestic version, but with an extra high-temperature filament so that it gives high illumination and high colour temperature for the price of a short lifetime. In nearly all cases solar simulators using a combination of these old technologies can only represent part of the solar spectrum at the same time and many have extremely elaborate and vulnerable reflector and filter systems to simulate the Sun’s radiation at all wavelengths.