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BULB DISCUSSION BOARDS => Antique Bulb Discussion => Topic started by: Ralph on October 21, 2005, 09:47:22 pm

Title: Old special purpose bulb - What might have it been used for?
Post by: Ralph on October 21, 2005, 09:47:22 pm

Here are a couple of pictures of an old bulb I found.

The base is a mogul bipin, the label on the bulb top reads: "Ultraviolet Spectrum,Base Down,
30A, 3.5V" and has the General Electric logo.

The bulb is about 10.5" tall, 3" diameter, and the "nose" is about 3.25" long and 1.25" diameter.

The glass appears to be the same type of glass normally used for this size bulb, but the end
of the "nose" appears to be a different type of glass (possibly pyrex?).

Does anyone know what the bulb might have been used for?

All thoughts and comments welcome.

Title: Re: Old special purpose bulb - What might have it been used for?
Post by: James on October 22, 2005, 04:53:27 am

Dear Ralph,

As its name implies, this is a lamp which produces radiation in the ultraviolet part of the spectrum.? All incandescent filaments produce a tiny amount of UV, but it is absorbed by the glass bulb.? However quartz glass will transmit the UV down to much shorter wavelengths.

This high power lamp employs a flat tungsten ribbon filament whose surface could be analysed to measure the spectral output, and it was used as a calibration source for UV spectrometers.? The main bulb is made of Corning's Pyrex glass, but the window is an optically flat disc of ground and polished quartz.? Via three intermediate glasses this is sealed to the pyrex bulb.? You can see the transition to each glass type along the length of the side arm.? They are needed because quartz cannot be sealed directly to Pyrex.? The two materials expand and contract at a different rate and the seal would crack.? The seal is thus made in 5 steps: Pyrex (Expansion coefficient 47 x 10^-6 mm / K), via GS35, GS25, GS10 glasses, and finally quartz (expansion coefficient 4).

During analysis of this filament it is important to work with one specific spot.? Similarly it is important to look head-on at the flat surface.? Viweing from an angle would give measurement errors.? You should see that one one edge of the ribbon there is a tiny nick taken out of its side.? Similarly on the glass bulb side directly opposite the side arm, a small arrowhead is engraved into the glass surface.? If you now look through the side arm at the filament, it is possible to look such that the arrowhead points directly at the indent in the filament.? You can then be sure that you are looking absolutely perpendicular to the filament surface, and will get a reliable measurement.

Its quite an unusual lamp and rather rare.? They were made up to the 1980s but you see very few of them around today.? Deuterium lamps give a much stronger UV spectrum and make far better calibration sources.

Best regards,

James.

Title: Re: Old special purpose bulb - What might have it been used for?
Post by: Ralph on October 23, 2005, 09:18:57 am

James;

         Thanks for the info - I didn't think tungsten filaments could get hot enough for ultraviolet.

         I can see the glass transitions but I am still looking for the filament notch and etched arrow - will
have a couple of friends take a look.

         It sounds like you might have had experience using the bulb.

Thanks Again and Best Regards!
Ralph

P.S. - Here is a little bit of my glass collection: