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From: roberts@CMR.NCSL.NIST.GOV (John Roberts)
Newsgroups: sci.space
Subject: The great light bulb debate
Message-ID: <9011092213.AA05755@cmr.ncsl.nist.gov>
Date: 9 Nov 90 22:13:28 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: National Institute of Standards and Technology
	formerly National Bureau of Standards
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Apologies if this is out of date. SPACE Digest has been down for about a week.

>Date: 29 Oct 90 16:07:30 GMT
>From: usc!cs.utexas.edu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca!neufeld@ucsd.edu  (Christopher Neufeld)

>>>     On one of the shuttle missions, send up thousands of tiny glass
>>>spheres with small holes in them.  Once in space, expose the spheres to
>>>the vacuum of space and then seal them.  Bring them back to earth
>>>and sell them to people.  Everyone can own their own piece of space!
>>
>   A glass ball with a vacuum inside is a bad thing to have around. If
>it is broken it implodes, and the pieces fly through the centre of the
>sphere, and on across the room at high speed. People doing vacuum
>experiments prefer metal containers whenever possible to prevent the
>formation of shrapnel. You'd need a plexiglass shield around the vacuum
>sphere to make it safe.
>   I'd hesitate to hold even a 1mm diameter vacuum sphere in my hand. If
>it shattered it would send glass into my palm, and you don't want to
>consider what would happen if you held it close to your face so that you
>could see the tiny sphere more clearly........

> Christopher Neufeld....Just a graduate student  | "The pizza was just a

..............................

>Date: 30 Oct 90 17:26:15 GMT
>From: news-server.csri.toronto.edu!utgpu!utzoo!henry@rutgers.edu  (Henry Spencer)

>Modern light bulbs are filled with argon, not vacuum.  (Expensive ones
>use krypton.)  

As you imply, the old bulbs were evacuated. I believe the main reason for the
switchover to inert gas was to reduce the rate of evaporation of the 
filament at a given temperature.

The "inert" gas usually cited in the literature is nitrogen. Why would 
krypton be better than argon? 

Halogen lamps use a halogen gas, which absorbs the tungsten evaporated
from the filament (and redeposits it?), allowing the filament to be operated
at higher temperature and efficiency.

>CRTs are quite dangerous to handle "naked", and people
>who work with them are careful; when enclosed in a monitor, one of the
>safety requirements is that the faceplate be tough enough that an
>implosion would not send fragments toward the user.  Safety-certification
>agencies like UL and CSA test this regularly.

>Chris N. is not kidding about the serious safety implications of glass
>vacuum containers.  However, a quick fix would be to encase them in 
>plastic.

For instance, I believe flash bulbs pretty much always explode when fired,
but the plastic coating holds the glass together.

>"I don't *want* to be normal!"         | Henry Spencer at U of Toronto Zoology
>"Not to worry."                        |  henry@zoo.toronto.edu   utzoo!henry

..............................

>Date: 30 Oct 90 14:24:53 GMT
>From: thorin!grover!beckerd@mcnc.org  (David Becker)
>Subject: Re: A great idea on how to fund NASA!

>Your average incandescent bulb holds slighlty pressurized inert gas.  Glass
>that thin could never keep O2 out of vacuum.  The pressure is to keep
>the O2 out and the filament burning.

>David Becker		   I Dweam of Dweanie
>beckerd@cs.unc.edu

Then how do you account for the working of the old-fashioned bulbs? Remember
the scenes from the old films, such as the encounter between W.C. Fields
and the blind man, in which light bulbs break with a loud BANG? (One of my
favorite scenes from "Our Gang" is the one in which the city kid gets across
a busy street by breaking a light bulb. The drivers all stop to check for
blown inner tubes, and the kid just walks across. :-)

Fluorescent tubes also contain near-vacuum. If one obtains a burned-out tube
and purely by coincidence just happens to shoot it with a pellet gun from
50 yards away, the result is a very interesting "thunk" as the tube fills 
with air, and fragments of glass will travel several feet. (One should then
be very careful cleaning up the glass, though with the absence of beryllium
in modern tubes, I suppose a cut wouldn't be quite as fatal as in the old 
days.)

The decorative "plasma spheres" also contain a pretty good vacuum, as do 
radiometers.

Disclaimer: Kids, don't try this at home without a signed letter of permission
from your congressman!
       John Roberts
       roberts@cmr.ncsl.nist.gov