What is HID and how does it operate?

Summary:

HID stands for High Intensity Discharge. It refers to lighting technology that relies on an electrical charge to ignite xenon gas contained in a sealed bulb. The technology of HID automotive lamps is similar to that of common vapor-filled street lamps. HID lighting doesn't have a filament but instead creates light by igniting an arc between two electrodes. HID lights get their name from the intense white light produced by the electrical discharge. HID lamps are also called xenon lamps, referring to a gas inside the lamps. HID general lighting has been used for years in sports arenas and stadiums around the country.


HID - High intensity Discharge

Like the name implies, high intensity discharge lighting creates a very bright light that is ideal for night time driving. Though the color of the light is often perceived as having a bluish tint when viewed at night, most of the light that is produced by HID headlamps is actually very close in color to natural noontime sunlight -- though some of the light produced is also in the blue and ultraviolet spectrum. Halogen headlamps, by comparison, are more yellowish in appearance but are brighter and whiter than older incandescent style headlamps.

The near-white light produced by HID headlamps improves visibility and makes it easier to see distant objects.

The color of light can be measured in "degrees Kelvin," which refers to the "temperature" (shade) of light. Natural sunlight at noon is 4870 degrees K. Light produced by a standard HID xenon bulb is 4300 degrees K. Light from a standard halogen bulb is 3200 degrees K, and that from an ordinary incandescent bulb is 2800 degrees K. The lower the temperature rating, the more yellowish the light appears.


Blue-white light is better for visual perception, but yellow light is actually somewhat better for reducing glare in fog, rain and snow (that's why some fog lights are yellow).


The xenon bulbs that are used in HID lighting systems also produce three times the light output of standard halogen headlamps (3000 lumens versus 1000 lumens), and require less energy (35 to 42 watts versus 55 watts). This is possible because HID lighting systems work like a vapor-filled street light or metal halide lamp. HID bulbs typically produce 71 lumens of light per watt compared to 18 lumens of light per watt for standard halogen bulbs.


HOW HID HEADLAMPS OPERATE

HID lighting systems use a special quartz bulb that contains no filament and is filled with xenon gas and a small amount of mercury and other metal salts. Inside the bulb are two electrodes separated by a small gap (about 4 mm or 3/16th inch). When high voltage current is applied to the electrodes, it excites the gases inside the bulb and forms an electrical arc between the electrodes. The hot ionized gas produces a "plasma discharge" that generates an extremely intense, bluish-white light.

CAUTION: Once ignited, the pressure inside an HID bulb builds to over 30 atmospheres due to heat (up to 1500 degrees F inside the bulb!). This creates a potential explosion hazard so do not attempt to power a HID bulb outside of the headlamp assembly to "test" it. Also, the bulb must be in a horizontal position when it is on, otherwise it may overheat and fail.

Like street lamps and fluorescent bulbs, HID headlamps require a high voltage ignition source to start. It typically takes up to 25,000 volts to start a xenon bulb, but only about 80 to 90 volts to keep it operating once the initial arc has formed. The normal 12 volts DC from the vehicle's electrical system is stepped up and controlled by an igniter module and inverter (ballast), which also converts the voltage to AC (alternating current) which is necessary to operate the HID headlamps properly.

The ballast adjusts the voltage and current frequency to operating requirements. The AC ballast frequency is usually in the 250 to 450 Hz range.

Power to the HID system is usually routed through a relay and fused at the power distribution center.

When HID headlamps are first turned on, the light appears more bluish but quickly brightens as the bulbs warm up. On most applications, the HID headlamps are only used for low beams (conventional halogen high beams are used). But on some of the newest HID systems, the position of the shielding around the bulb changes position to provide both high and low beams.

Because there is no brittle filament inside a xenon HID bulb to break or burn out, the headlamps typically last up to three times longer than halogen headlamps (3000 hours versus 1000 hours of continuous operation, which is equivalent to 5 to 10 years of normal driving).

How Does HID Adapt to Dual Filament Halogen Bulbs?

There are two versions of dual beam HID setups that would be required for cars (such as the Nitro) that uses a factory dual filament Halogen Bulb.

Ver. 1: This special dual-bulb version generates regular and high beams in one single base utilizing a HID capsule for the low beam and a halogen bulb for the high beam. This solid-state design definitely outlasts the moving mechanism design. Another plus is that this design is cheaper due to the lack of controllers which are required for controlling the mechanism.

Ver. 2: This is a single-capsule that generates regular & high beam patterns using a movable shutter. It is more expensive due to the required controllers as mentioned above. But one's eyes see a constantly agreeable light and do not have to continually re-adapt between the two colors/intensities/clarities. Moreover, apart from the setting mechanism for the shutter, additional expenditure for a separate headlamp with its own control electronics is no longer necessary. This saves energy, money, construction space and weight, and helps reduce fuel consumption.

Version 2 is currently offered as our FLASHTECH Bixenon HID lighting system.