Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!know!sdd.hp.com!ucsd!ames!skipper!rando From: rando@skipper.dfrf.nasa.gov (Randy Brumbaugh) Newsgroups: sci.electronics Subject: Re: Do Halogen lamps need ballasts? Summary: halogen lamp info ` Message-ID: <714@skipper.dfrf.nasa.gov> Date: 28 Nov 90 20:46:38 GMT References: Distribution: sci.electronics Organization: NASA Ames-Dryden FRF, Edwards, CA Lines: 59 Someone asked what the halogen gas did for these lamps. Hope this helps . . . (In this posting, "lamp" means light bulb, not a lighting fixture). A "halogen" lamp (also sometimes called a "quartz", "tunsten- halogen", or a "Quartz-iodide" lamp) is basically the same as a regular incandescent lamp -- it produces light by heating a tungsten filament in a sealed envelope containing some gas. It is still a form of incandescent lighting. No ballast is needed for halogen lamps, although some small fixtures use lower voltage lamps and need a step-down transformer. The difference is in the envelope, which is made of quartz to handle the high temperature operation needed; and in the gas which fills the envelope. The gas is a member of the halogen family. Regular incandescent lamps use an inert gas. In a regular incandescent lamp, the tungsten "boils" off the filament during operation. It eventually contacts the cooler glass envelope, where it deposits itself. This results in darkening of the envelope as the lamp ages, and in weakening of the filament. A chemical process (the halogen cycle) is used to improve this in these new fangled "halogen" lamps. The tungsten chemically bonds with the halogen gas in the envelope. When the gas contacts the hot filament, the chemical bond is broken, and the tungsten is re-deposited in the filament. These lamps won't last forever, because the tungsten isn't deposited at the same spot it came off the filament. This gives lamp designers 2 options: - make the lamp produce brighter, higher color temperature light at the same life expectancy. -OR- - make the lamp the same brightness with a longer life. To maintain the halogen cycle, the lamp must run at fairly high temperatures and pressures. Dimming may reduce this somewhat, and cause the envelope to darken, but operating a while at full brightness will reverse the process. Also, the quartz envelope shouldn't be touched by bare hands -- oils on the skin will weaken the structure and may cause bubbles or lamp failure. Tungsten-halogen (T-H) lamps are now used almost exclusively for stage and television lighting applicatuions, where they have been around for quite a while. This is due to thier longer life/higher color temp and the fact that light output does not decrease as the lamp ages, as it does with regular incandescent lights. Randy Brumbaugh rando@skipper.dfrf.nasa.gov