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Path: utzoo!utcs!lsuc!msb
From: msb@lsuc.UUCP (Mark Brader)
Newsgroups: net.consumers
Subject: Re: light bulbs
Message-ID: <374@lsuc.UUCP>
Date: Wed, 6-Feb-85 22:28:09 EST
Article-I.D.: lsuc.374
Posted: Wed Feb  6 22:28:09 1985
Date-Received: Wed, 6-Feb-85 23:31:28 EST
References: <3362@alice.UUCP> <681@aluxe.UUCP> <669@whuxlm.UUCP>
Reply-To: msb@lsuc.UUCP (Mark Brader)
Organization: Law Society of Upper Canada, Toronto
Lines: 28
Summary: running hotter does not mean producing more heat

Quote battle abridged:

> > > Light bulbs that last longer do so by running cooler, hence more
> > > efficiently.
> > 
> > ...  Tungsten lamps that run cooler give off much less
> > light per watt, thus ... the efficiency is very very low.
> 
> There is an inconsistency in the reply above.  "Much less light per watt"
> means that there must be, correspondingly, much more heat per watt.  This
> would lead to running hotter, not cooler.  Bulbs have only two forms
> of power dissipation - heat radiation and light radiation. ...

You must remember that heat is not the same as temperature.  You can put
your hands into an oven where the air is at 450 degrees F, and not get
burned -- but try touching metal or water at 200 degrees F, and you will.
The air is less massive* so it carries less heat.

The FILAMENT of a long-life bulb runs cooler than that of an ordinary
bulb, which helps it last longer; but as the last quote points out,
the bulb has to dissipate energy somehow, since it gives less light
per watt, and so, yes, the bulb as a whole must give out more heat.

Conclusion: a long-life bulb must have a larger filament, so that it
can give out more heat without being at as high a temperature.
The bulb runs warmer, the filament cooler.

Mark Brader