Lighting:
Metal-Halide Lighting (Also known as High Intensity Discharge or HID)

By Lance Kaczorowski, Guest Writer

Chemicals categorized as metal-halides (such as lithium iodide) are added inside the bulb envelope to improve the color of the light. 

For example, lithium adds a strong red color to the mix of colors produced by the light bulb.

Impressive Color Rendering

The color rendering of metal-halide bulbs is impressive, and they have high efficiency.  They tend to cost more than their mercury vapor cousins, but find their way into the same applications as mercury vapor lights.

Long Warm-Up Time

Like mercury vapor lights, metal-halide lights have a long warm-up time.

Xenon Metal Halide

Automotive Lighting

One notable special application is automotive lighting. HID lighting initially was found only on high-end luxury cars in Europe.  They are now found on about half the cars sold in Europe, and are gaining rapid acceptance (in spite of their high cost) in the United States.

One obvious hurdle to adapting HID to cars was the very slow warm up time.  For all practical purposes, vehicle lighting needs to be "instant on."

Modifying the ballasts and the bulbs to tolerate such use has been an ongoing development process for HID manufacturers.  Starting an HID bulb rapidly shortens its life.  And as was true for fluorescents, the more often you turn the bulb off and on, the shorter the life.  Fortunately, the life
reduction occurs from cold restarts, not hot restarts.  If your lights are warmed up and you flash your lights, you won't reduce the bulb's life noticeably.

Longer Life Expectancy

Automotive HID life expectancy is about 2000 hours, which is twice the 1000 hours you'd expect from some high-end halogen bulbs, but is a much shorter life than non-automotive HID bulbs.  Automotive HID bulbs, though, are more efficient and produce much more light than halogen bulbs.  A 35 watt automotive HID bulb will produce more light than a 65 watt automotive halogen.

Bluish Color

Even though the addition of metal-halides improves the color, the color is still strongly bluish, which is evident when you see a car with HID bulbs approaching you at night.  The bulbs also slightly change color with age. If one bulb is replaced, both should be replaced to maintain a uniform appearance of color.

Thanks to our guest lighting expert - Lance Kaczorowski, who brings a wealth of expertise to the site: