Hi Kurt, 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. To see what spectral lines Neon will produce take a look at the table near the bottom of this link: http://www.newport.com/file_store/PDFs/tempPDFs/e5395_Oriel-Pencil-Style-Cal ibration-Lamps.pdf It is a pretty broad list. On another note, placing the lamp behind a slit will work well provided that the slit is at the telescopes focal point (infinity). Perhaps placing the neon bulb on Patrick's house will make it stellar like from SPOC <g>. I'm not sure of the line of sight here. Using a diffraction grating at the eyepiece will require that the calibration source is similar to the stars. If you place it close to the telescope it will not be stellar but merely flood the entire aperture with the light and thus you won't see any lines. A thought here: perhaps reflecting the neon light image off a small white Christmas tree ornament some distance away from the telescope but not at infinity would work. I remember figuring a mirror with John Dobson we used the Sun's glint from such a bulb about 300 feet away worked pretty well as a point source. It did have a small amount of spherical aberration but we were able to get it pretty close. Maybe Brent Watson could comment on this. Jerry Foote ScopeCraft, Inc. 4175 E. Red Cliffs Dr. Kanab, UT 84741 435-216-5450 jfoote@scopecraft.com