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Light bulbs and heat

To: british-cars@autox.team.net
Subject: Light bulbs and heat
From: Simon.Matthews@tiuk.ti.com
Date: Mon, 13 Jun 94 09:18:51 BST
Roland Dudley <cobra@cdc.hp.com> says:
<<<<<
At home I pulled the old rear bulbs, donned rubber gloves and installed
the new halogen.  When I bought them the clerk had asked me if I had
glass or plastic lenses.  "Glass", I had answered confidently.  But it
seems my middle-aged memory had failed me again.  The lenses are plastic
after all.  Sigh.  Oh well, only the lenses are plastic, everything else
is metal and the bulbs are completely open at the sides and back.  There
are no reflectors to confine the heat.  I decided to give the bulbs a
trial run anyway.  I turned the lights on for a few minutes to see how
hot they got.  I even turned on a turn signal.  After five minutes or so
I held my had behind a bulb about the same distance the lens was in
front of it.  No noticeable heat.  I'm going to go with this for now but
keep a close watch.  The bulbs are noticeably brighter but I couldn't
tell if there was enough improvement to make them easily visible in
direct sunlight.  I never had that much trouble seeing them myself but
apparently other people have.
>>>>>>>
I don't like to be pickey about this, but there should be less heat, not more.
If the bulbs are rated at the same wattage (ie. energy input) and a greater 
proportion of that energy is emitted as visible light (ie. they are brighter),
then it follows that a smaller proportion must be emitted as heat. 

Simple really!

Simon Matthews


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