I once saw a clever demo using a yellow LED on a long enough AC cord that it could be swung in a circle. If it went fast enough, the light was broken down into red and green alternating flashes. The lamp no doubt had a built-in circuit that took advantage of the AC current, as well as the fact that the human eye/brain interprets a combination of red and green light sources to be yellow light (if you don't believe that, look closely at a color TV: you won't see any yellow dots). John R. Peterson I'm not sure if the Radio Shack yellow LED is the same as

In a prior post 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.