As a PhD in electrical engineering that works with infrared radiation (heat to
the rest of you) I should know be able to answer a few questions on the
subject. The first topic is heat from light bulbs. The light bulb is little
more than a low value resistor. It is like a miniature heating element on an
electric stove. With the stove, the hotter it gets, the brighter it glows.
This is because of the theory of black body radiation, which is boring to even
me.... The gist of it is that the hotter an object, the more radiation it
gives off. As it gets warmer, it gives off more visible radiation. First in
the red (closest to the infrared) then orange, yellow, green, blue, and then
ultra violet. A regular incandescent bulb is therefore quite hot (~3000K for
those who want to know :-) for it to appear white. At this temperature the
filament is slowly evaporating itself. For this reason the bulb slowly appears
to get dimmer as the filament deposits itself on the envelope.
The new high pressure halogens have a gas that inhibits the filament from
evaporating. Because of this, the filament has been redesigned (thinner,
though it may be thicker). This redesign is to reduce the resistence. The
lower the resisence, the greater the current flow for a given (12 V) voltage.
This higher current leads to greater power and higher temperature, ultimately
leading to more light. For a set power, the halogen is still at a greater
temperature than the traditional bulb so one gets more light out.
Verdict: Halogens are great for headlights where more light is the ultimate
goal. For tail lights, there is a better alternative, the LED. LEDs emit
light over a smaller portion of the spectrum, with far less heat generation.
They also take much less current that either the incandescent or halogen bulbs.
For this reason, you see more red LEDs being used in brake lights. Many cars
will have the entire rear wing emblazoned with red LEDs. If these were regular
bulbs, you would drain a battery very quickly. Unfortunately, it is impossible
to make white light LEDs to replace head lights. This is easily explained, but
probably belongs on the alt.lucas.replacement list
MAD, the rambling IR man, courtesy of your Uncle Sam
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