Re: Slightly OT. Heat and a Bench Light ...

On Fri, 4 Jul 2008 01:23:49 +0100, "Arfa Daily"
<arfa.daily@xxxxxxxxxxxx> wrote:

I have noticed that these new smaller bulbs run a whole quantum leap hotter
than the older larger size, and they hot up the shade on the bench light
until it is unbearably hot to touch.

As I understand it (possibly wrong), the higher the temperature of the
filament, the more efficient the incandescent light bulb in lumens per
watt. There's a bit of a clue at:
<http://en.wikipedia.org/wiki/Incandescent_light_bulb>
During ordinary operation, the tungsten of the filament evaporates;
hotter, more-efficient filaments evaporate faster. Because of this,
the lifetime of a filament lamp is a trade-off between efficiency
and longevity. The trade-off is typically set to provide a lifetime
of several hundred to 2000 hours for lamps used for general
illumination. Theatrical, photographic, and projection lamps may
have a useful life of only a few hours, trading life expectancy
for high output in a compact form. Long-life general service lamps
have lower efficiency but are used where the cost of changing the
lamp is high compared to the value of energy used.

In other words, the newer smaller bulbs are trading efficiency for
lifetime, which is the result of running hotter. I'm not sure why the
bulb is smaller. My guess(tm) is that it's simply thicker, which
allows the use of a smaller bulb size, which can withstand the heat
better than a thin bulb and can handle a higher internal gas pressure
(which is necessary to prevent filament evaporation).

More on the subject:
<http://en.wikipedia.org/wiki/Luminous_efficacy>
<http://members.aol.com/ajaynejr/lumen.htm>

--
Jeff Liebermann jeffl@xxxxxxxxxx
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
.

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