On another note, placing the lamp behind a slit will work well provided that the slit is at the telescopes focal point (infinity).
Thanks, Jerry. It looks like I'll have to rethink my plan of whether a light source behind a slit and held in front of the telescope objective will give useable calibration lines for a slitless stellar grating. But, I think I'll still work on the idea and at least give it a mock-up test on a telescope, if only for the hobby entertainment value. Even if I have go to a "slit" spectrograph, a small portable hobby calibration source would be helpful to have, rather than a bulky cold flourescent light.
Regardless of which neon light you get from Radio Shack, you will need to remove any colored lens over the bulb. Otherwise the full neon spectrum will not be usable.
I bought several of these yesterday, but saw no way to remove the housing covering without the bulb. In a prior post, Chuck and Jerry wrote:
Jerry, for convenience, how about one of those small house-current continuity testers? They typically have a neon bulb, and a lamp cord coud be spliced onto the contact leads.
Yesterday, I bought packets of red, yellow and green neon mini-bulbs (120 VAC, 3mA) from Radio Shack and a $5 "Extech" neon bulb household current tester at Sears. Turns out the Radio Shack bulbs can be directly connected to AC household current without modification and they will work. Appropriate precautions to assure against accidental electrocution where taken during testing. Testing each one in turn with and without a slit and a hand-held student ProjectStar spectrometer, the results where: 1) green neon - makes a strong yellow line at 5800 and a series of red lines between 6000 to 6100 Angstroms. Also produces an distracting continuous spectrum between 4000-5700 A. Dimmest of the three RadioShack bulbs. 2) red neon - slightly brighter - makes the emmission lines as with the green neon plus a dim blue line at 5300 A. 3) Ektech household current tester - pinkish colored - makes two distinct lines - blue at 5300, yellow at 5800 and the series of red lines between 6000-6100 A. Makes the sharpest lines without a slit. Unclear if the bulb can be removed from the housing without destroying the unit. Plastic housing is incompatible with use in an electronics project box. 4) yellow neon - significantly brightest of the three bulbs - makes two distinct lines - blue at 5300, yellow at 5800 and the series of red lines between 6000-6100 A. Lines less defined than the Extech. This was the clear winner. The Radio Shack yellow neon bulb is embedded in a plastic housing that attaches to project boxes by two hexagonal nuts on either side of a project box wall. This suggests a physical set up of 7 bulbs - 1 in the center surrounded by 6 bulbs - that are banked in three toggle switches. 1st switch - 1 bulb, 2nd switch - add 3 bulbs for a total of 4, 3rd switch - add 3 bulbs for a total of 7. I have bought six yellow bulbs and the other misc parts and will let you know how it works out. Thanks for the help. - Kurt