Roland Dudley just has to bring up:
> Just out of curiosity, how efficient are halogen bulbs? If a higher
> percentage of the energy is converted to light then higher wattage
> doesn't necessarily mean hotter bulb (as in the case for fluorescent
> vs incandescent lighting). Anyone have comparative data? Pat V?
Shoot, I was *trying* to avoid this discussion, but since you asked... ;^)
No, Halogens are not more "efficient" than regular tungsten filament bulbs.
That's primarily because the filament in a halogen bulb is made of ....
tungsten!
The advantage of a halogen bulb (so called because of the addition of a
halogen gas to the bulb, usually florine or bromine I think) is that the
filament can be burned hotter than with a regular bulb, giving more light
output, usually with better life. (In fact, the bulb _has_ to burn hotter,
as I'll explain in a moment.)
The tungsten filament in a regular bulb is slowly spalling off tungsten
atoms whenever it's on, which plate out on the inside surface of the bulb.
This eventually weakens the filament to the point that it breaks. If you were
to put more current through the filament, making it burn hotter, this effect
would be accellerated, "burning it out" sooner. I don't remember all of the
gory details of the actual mechanism, but the effect of the halogen gas is to
essentially intercept the tungsten atoms and, above a critical temperature,
"recycle" them back on to the filament. (This critical temperature is like
1000 - 1200 degrees Celsius! This is why it's not a good idea to put
halogen bulbs on a dimmer - they will actually "burn out" sooner if run
dimmed below this critical temperature than if they're run at full chat!)
So you get better life with halogen bulbs, but no more light than you would
with a regular bulb running the same filament temperature.
Mike Burdick <mburdick@unmc.edu> guesses:
> Not exactly data but: For cars with electrical systems designed for
> halogen headlights, there are usually warnings NOT to use conventional
> bulbs as replacements. When I asked why, someone who knew said that
> halogen bulbs draw less current.
Maybe, but not necessarily. A halogen bulb designed to give the same light
*output* will consume less power than a standard bulb. (The filament is
smaller and thinner so it burns hotter per unit length of filament for the same
amount of current passing through it.) But the reason most people replace
standard bulbs with halogens is to get *more* light output, which invariably
means more current and more total heat.
BTW- to Chris, who started this whole mess, replacing the 1157s in your TR4A
with the halogen equivalents will probably make the flash rate of your turn
signals increase. I guess that could probably give the illusion of taking
corners all that much faster! ;^)
Pat Vilbrandt Fluke Corporation Everett, Washington USA
pwv@tc.fluke.COM or: { uunet, uw-beaver, sun, microsoft }!fluke!pwv
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