Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!sdd.hp.com!uakari.primate.wisc.edu!dali.cs.montana.edu!ogicse!zephyr.ens.tek.com!orca.wv.tek.com!pogo!bobt From: bobt@pogo.WV.TEK.COM (Bob Tidrick) Newsgroups: sci.electronics Subject: Re: Do Halogen lamps need ballasts? Message-ID: <10147@pogo.WV.TEK.COM> Date: 29 Nov 90 20:42:34 GMT References: <714@skipper.dfrf.nasa.gov> <1147@inews.intel.com> Reply-To: bobt@pogo.WV.TEK.COM (Bob Tidrick) Distribution: sci.electronics Organization: Tektronix, Inc., Wilsonville, OR. Lines: 30 >>in these new fangled "halogen" lamps. The tungsten chemically New fangled they are not. The have been around quite a while. >>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. One thing that has bothered me about these Halogen lamps with the dimmer is, from my experiance if the bulb is not kept at least at a certian high temperature they will fail faster. I have seen halogen bulbs grow tungsten crystals on the ends of the filament when run at a lower then rated voltage. Apparently this is because when the filament is at a lower temperature the tungsten is not redeposited on the filament while the bulb is operating. When it is turned off and the gas cools it is deposited at the coolest point. In this case the ends of the filament. The crystals grow depleating the material on the rest of the filament. Hot spots do occur but there is always some tungsten trapped in the gas when the bulb is turned off it cools and again is deposited on the crystals. The bulbs we used where rated at about 5000 Hrs. Most of them lasted about 2000. Some lasted as little as 500 Hrs. These were bulbs rated at 12 Volts being run at 10V. I wonder if the manufactures of these lamps know about this? -- Bob Tidrick GPID Engineering Tektronix Inc. Wilsonville OR.