To All,
I have a perplexing question on some plain incandescent light bulbs.
I bought a package of four ordinary Sylvania 25 Watt 120 volt
candelabra light bulbs to act as current limiters in a HVDC supply.
The manufacturer's code is 25B10C/BL/4PK.
Here's a picture:
http://www.servicelighting.com/catpics/sylvania/13452.jpg
After the purchase, I opened the package to check the filament
resistance. All four bulbs were open!
I applied 120VAC and each bulb lit normally. Afterwards, each bulb
read about 46 ohms on a DVM.
The next day, three of the four bulbs were open. After applying
120VAC again, they all read about 46 ohms.
I examined the bulbs carefully under a microscope. Everything seems
normal. The crimps at the filament look normal. The welds on the
lead wires seem fine.
I removed the base from one of the bulbs to check if anything
strange was inside. There was nothing. The wires go straight into
the bulb.