High Intensity Discharge (HID) lighting technology replaces the filament of the light bulb with a capsule of gas. The light is emitted from an arc discharge between two closely spaced electrodes hermetically sealed inside a small quartz glass tubular envelope capsule. To operate, they require ballasts, which supply proper voltage and control current. The amount of light produced is greater than a standard halogen bulb, while consuming less power, and more closely approximating the color temperature of natural daylight.

In all High Intensity Discharge lamps, light is produced by passing a current through a metal vapor. Free electrons colliding with an atom in the vapor momentarily knock an electron into a higher orbit of the atom. When the displaced electron falls back to its former level, a quantum of radiation is emitted. The wavelength of radiation depends on the energy zone of the disturbed electron and on the type of metal vapor used in the arc tube.

Although it produces 5% of its output when first ignited, the HID light requires a few seconds (usually 15-20) to come up to full output. Also, if power to the lamp is lost or turned off, the arc tube must cool to a given temperature before the arc can be re-struck and light produced.

What are the advantages of HID lights over conventional halogen primary lights?

More light output An 18 Watt HID light source produces approximately the same lumens at the light source as a 55 Watt halogen bulb at a three to five times the halogen's efficiency. The 10 Watt HID only produces ~500 lumens, but thanks to its true 6000K color temperature it appears almost as bright as a 55 Watt halogen bulb when in use. The HID lamp's lumens per watt (LPW) efficacy is roughly six to eight times that of an incandescent lamp.

Whiter light. The color temperature of HID lighting more closely approximates the color temperature of natural daylight than does a halogen system, which appears yellowish in comparison. We use the term "correlated color temperature" to indicate that the light appears as if the discharge lamp is operating at a given color temperature-- traditional measurements of color temperature are drawn from the properties of the metal used in the bulb's filament. Typical color temperatures are 2800K (incandescent), 3000K (halogen), 4100K (cool white or SP41 fluorescent), and 5000K (daylight-simulating fluorescent colors). A white light has a perceived brightness which may equate to the higher stated efficacies-- ie., although an HID lamp might have equivilant lumens as a higher wattage halogen bulb, the HID will appear brighter and more pleasing to the eye than the output of a halogen lamp.

Longer Service Life. An HID lamp will last, on the average, 3 to 5 times as long as a halogen bulb. In normal use, your HID bulb should last beyond one thousand ignitions.

Ballasts

Ballasts are not interchangeable among different types of HID lamps. A ballast design incorporates electronic circuitry to provide specific lamp/ballast operating characteristics. As an example, the effects of line voltage variations on resultant changes of lamp wattage are a function of the ballast circuit design. Requirements for a circuit which will provide a finer degree of lamp regulation generally result in a higher ballast cost.

Care and Troubleshooting of your HID Light

The light emitted from the HID arc tube is intense and appropriate safety precautions relating to exposure protection are required. Metal halide bulbs operate at very high temperatures and pressures. The quartz glass of the bulb itself must be kept clean. The glass lamps should be handled with care giving special attention of the quartz arc tube. The HID light is a DC lamp; proper electrical wiring polarity must be observed to prevent damage to the lamp.

CAUTION: Ultraviolet, visible, and infrared radiation is emitted from metal halide lamps. Possible skin or eye irritation can result from exposures exceeding 15 minutes. Do not stare at exposed lamp in operation. During operation, the bulb should be enclosed in a housing to prevent injury. Do not remove bulb from equipment until it has cooled. Never handle the bulb when it is operating!

Protect the quartz arc tube when handling the lamp. Keep the arc lamp clean. Do not touch the quartz tube, the inside surface of the reflector, and the connecting wires. Contamination can degrade lamp performance or cause premature failures. If necessary, clean the lamp by wiping with a lint free towel or swab immersed in denatured alcohol.

While HID bulbs last considerably longer than halogen bulbs, you should be aware of several characteristics that indicate that a bulb is approaching the end of its lifespan. Initial symptoms of end-of-life are characterized by low light output and/or intermittent starting. Visual signs include blackening at the ends of the arc tube and electrode tip deterioration. Note that HID bulbs contain metals, including mercury, that are harmful to the environment. Please be responsible in securing proper disposal of an HID bulb.

The bulb and ballast are sensitive to external operating temperature. Although the HID light doesn't generate the amount of heat of a halogen light, it should be treated like any other dive light. The HID lamp should only be operated while in the water, to provide proper cooling for the lamp assembly. While transporting your HID light, please don't leave the light in direct sunlight or in a car's interior on a hot day.

If you are experiencing problems with your HID light ahead of its expected lifespan, take a second to inspect the bulb and ballast assembly:

• Inspect for broken arc tube or outer lamp jacket
• Check connection where lamp broken where glass meets the base
• Make a visual inspection of the bulb for broken or loose components in lamp envelope
• Inspect for arc tube end blackening
• Inspect for deposits inside the outer glass envelope