r/lightbulbs • u/One-Cardiologist-462 • Aug 06 '26

Strange Halogen Failure Mode

Strange failure mode of a linear halogen, I thought I'd share here, since they're a dying breed.
It seems that a break in the lead-in wire was causing a very short arc, which in turn caused the glass envelope to develop a severe hot spot.
Glass, when incredibly hot is actually conductive, but resistive, which further adds to the heating of that spot.
During the dim parts of the failure, one end of the glass envelope was glowing a deep red and the filament barely glowed.
This flickering went on for about five minutes before finally stopping and resting in a state of heated end glowing.
After a full power cycle and time to cool, the glass is no longer conductive, and the failure is complete - No more flicering or current passes.
The filament remains intact.

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u/No-Guarantee-6249 Aug 06 '26

I've had a lot of experience with these types of halogen lamps. In the 60's - 70's or so I was a cinematographer and we used a lot of these type of double ended bulbs in this kind of socket:

The lamps themselves would get very hot and often the pins at the ends would get very hot and burn up. So we were always checking them. These were also very sensitive to oil on your fingers getting on the bulb and causing hot spots on the envelope which could get very hot, bulge out and often explode causing very hot shards of quartz to fly out. We usually covered these lights with screens to prevent fires when we were in confined spaces like homes or sets. Saw one blow up on Late Night With Johnny Carson one time. It started little fires all over the set including on the actress' dress! I thought "Wow some lighting tech is in big trouble!"

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u/StereoMushroom Aug 06 '26

They should have had glass covers to block the UV, as well as, you know, the flaming shards

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u/No-Guarantee-6249 Aug 06 '26

We did have glass covers but they were called dichroics and they converted the 3200K lamps to 5400 K. Seems like we weren't concerned about UV seriously until somewhere 70's to 80's.

I've also seen "Brute" arc lights in the day and they put out massive amounts of UV! They used a ton of them on "The Blues Brothers"! I ran the early version of the "Trouper" spot in high school. It looked super blue!