What
is HID? HID (High Intensity Discharge) refers to lighting
technology that relies on an high voltage electrical charge to produce
an arc between two electrodes in a gaseous mixture.
The technology
of automotive HID lamps is the same as that of high powered street
light. There are two common types of HID lighting; high-pressure sodium,
and metal halide. Metal halide, is the type used for headlights and
offers a bright white light, while high-pressure sodium, used in some
street lights, offers greater efficiency but a duller orange light.
Automotive
HID bulbs are filled with gases (including Xenon), mercury
and metal halide salts, they don't have a filament, but instead create
light by making an arc between two electrodes.
The arc sphere can be seen inside the outer protective glass envelope.
When the starting current of 23,000 Volts is applied to the electrodes
from the ballast, electrons
begin jumping the gap between the electrodes
and an arc is formed between them.
But where does the light come from?
During
their jump through the gas, some of the jumping electrons (red) collide
with atoms of the vaporized mercury and metal halides. On the outside
of these metal atoms are allot of circling electrons (blue) and like
a snooker ball, a red electron can knock a blue out and into a higher
orbit around its atom. During the collision energy is tranfered from
red to blue. When the blue electron falls back into its' place (the
lower orbit around the atom) it loses the energy given to it by the
red. It emitts this energy as light radiation.
The wavelength
(or colour) of this light radiation depends on the type of metals
used in the arc tube. So different mixtures of metals are used in
different colour temperature HID bulbs in order to get their particular
light output. None of our HID bulbs achieve colour by 'Blue coatings
or filters which would reduce the light output.
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to General HID page
