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.
