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From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Do Halogen lamps need ballasts? (Krypton bulbs)
Message-ID: <11997@milton.u.washington.edu>
Date: 30 Nov 90 05:32:31 GMT
References: <714@skipper.dfrf.nasa.gov> <1147@inews.intel.com> <36350@cup.portal.com>
Organization: University of Washington, Seattle
Lines: 27

In article <36350@cup.portal.com> schuster@cup.portal.com (Michael Alan Schuste\

>
>What's the principle behind the "krypton" flashlight bulbs being sold
>now, and market as "70% brighter" than the standard type?

	There are three major different types of incandescant bulbs.
Vacuum, inert gas, and halogen.  Vacuum bulbs are more energy-efficient,
and have a lifetime of circa 5-10 hours.  Inert gas bulbs have some 
gas-cooling of hot spots, so last longer (circa 750 hours), but still
blacken as they age.  Halogen bulbs do not blacken, but must be run
hot.
	Traditional flashlight bulbs have been vacuum types.  For larger
power outputs (which modern batteries make feasible), one can use a
very dense gas (Krypton) which has lower thermal conductivity than
Nitrogen (which is the fill gas in most 100W household lamps).
	The '70% brighter' effect is due to the filament running
hotter (and taking 50% more power).
	I tested bulbs of all three types for my bicycle light;
the vacuum bulb spectrum was dreadfully red.  The halogen and the
Krypton had the same color temperature, with the Krypton being
slightly higher power output.  I ended up using the halogen
(and have had a hundred or so hours use so far) but the Krypton
bulb is what I'll be replacing it with (the cost is circa 8:1
in favor of Krypton).

	John Whitmore


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