High-intensity discharge lamp
Metal-halide and ceramic metal-halide lamps can be made to give off neutral white light useful for applications where normal color appearance is critical, such as TV and movie production, indoor or nighttime sports games, automotive headlamps, and aquarium lighting.
High-pressure sodium lamps tend to produce a much whiter light, but still with a characteristic orange-pink cast.
Moreover, the presence of thorium in electrodes reduces the work function which again results in easier arc starting and sustaining.
More recently, HID lamps have been used in small retail and even residential environments because of advances in reduced lumen bulbs.
HID lamps have made indoor gardening practical, particularly for plants that require high levels of direct sunlight in their natural habitat; HID lamps, specifically metal-halide and high-pressure sodium, are a common light source for indoor gardens.
Exposure to HID lamps operating with faulty or absent UV-blocking filters causes injury to humans and animals, such as sunburn and arc eye.
Many HID lamps are designed to quickly extinguish if their outer UV-shielding glass envelope is broken.
The higher efficacy of HID lamps compared to halogen units means longer burn times for a given battery size and light output.
The majority of HID lamps are produced in the color temperature range of 5000K to 6000K, which is similar to natural daylight.
This is useful for applications requiring high levels of luminosity such as sport stadiums, warehouses, projection TVs, and gardening lights.
[12] However, for certain applications such as automotive headlamps, HID lamps are produced in nearly every color from yellow and white to blue and purple.
The highest wear occurs when the HID burner is ignited while still hot and before the metallic salts have recrystallized.
Another phenomenon associated with HID lamp wear and aging is discoloration of the emitted light beam ("fading"[14]).
Based on Planck's law, this is a direct result of the increased voltage and higher temperature necessary to maintain the arc.
Mercury lamps always require specialised disposal or recycling, which is legally mandatory in many locations depending on jurisdiction.
