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#Post#: 4--------------------------------------------------
what is HID?
By: zoopupaddict Date: August 19, 2012, 11:00 am
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HTML http://en.wikipedia.org/wiki/High-intensity_discharge_lamp
#Post#: 13--------------------------------------------------
What is HID?
By: zoopupaddict Date: August 19, 2012, 11:56 am
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HID stands for High-Intensity Discharge, the technical term for
the electric arc that produces the light. Automotive HID lamps
are commonly called Xenon Headlights because of the xenon gas
used in the lamps. The xenon gas allows the lamps to produce
minimally adequate amounts of light upon startup and speed the
warmup time. If argon were used instead, as is commonly done in
street and other stationary HID lamps, it would take several
minutes for the lamps to reach their full output. Xenon
headlights use a small, purpose-designed metal halide lamp and
produce more light than ordinary incandescent light bulbs
(including quartz halogen lamps). The light from Xenon
headlights has a distinct bluish tint when compared with normal
headlights. The high intensity of the arc comes from metallic
salts that are vaporized within the arc chamber.
Xenon headlamp bulbs produce between 2,800 and 3,000 lumens from
42 watts of electrical power, while halogen filament headlamp
bulbs produce between 700 and 2,100 lumens from between 40 and
65 watts. Because of the increased amounts of light available
from HID bulbs, HID headlamps producing a given beam pattern can
be made smaller than halogen headlamps producing a comparable
beam pattern. Alternatively, the larger size can be retained, in
which case the Xenon headlamp can produce a more robust beam
pattern.
An HID headlamp requires a ballast. The ballast converts the 12
volts used in automotive electrical systems to the several
thousand volts required to strike and maintain the arc.
Despite marketing claims to the contrary, HID headlamps' light
output is not similar to daylight. The spectral power
distribution (SPD) of an automotive HID headlamp is
discontinuous, while the SPD of a filament lamp, like that of
the sun, is a continuous curve.
The arc within an HID headlamp bulb generates considerable
short-wave ultraviolet (UV) light, but none of it escapes the
bulb. A UV-absorbing hard glass shield is incorporated around
the bulb's arc tube. This is important to prevent degradation of
UV-sensitive components and materials in headlamps, such as
polycarbonate lenses and reflector hardcoats. The lamps do emit
considerable near-UV light).
Vehicles equipped with HID headlamps are required by ECE
regulation 48 also to be equipped with headlamp lens cleaning
systems and automatic beam levelling control. Both of these
measures are intended to reduce the tendency for high-output
headlamps to cause high levels of glare to other road users.
The arc light source in an HID headlamp is fundamentally
different from the filament light source used in
tungsten/halogen headlamps. For that reason, HID-specific optics
are used to collect and distribute the light. Installing HID
bulbs in headlamps designed to take filament bulbs results in
improperly-focused beam patterns and excessive glare, and is
therefore illegal in many areas.
Read more @
HTML http://wikicars.org/en/Xenon_Headlights
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