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I have a desk lamp that uses G4 bi-pin light bulbs.

The socket is marked "JC G4 12V max 20W". I was wondering what the "JC" means, so I googled "JC G4" and indeed a lot of results show up, some with "JC type bi-pin" in the name.

However, I can't find what exactly is a "JC type" light bulb. I thought the "G4" already mechanically describes the light bulb.

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JC : J From the word “Jod” – It means “Iodine” in German and indicates that it is a Halogen lamp. C From the word “Cine” Indicates that the primary application for lamp is Cinema but can include Optics & Projection & Other Markets

This halogen bulb is a low voltage bulb, commonly found under counters, in desk lamps, or as accent lighting. This type of bulb can be be purchased in various low voltage amounts, ranging from 6 to 28 volts. This bulbs come in capsule shape and have two pins at the base of them. There are two different sizes, a G4, which is 4 millimeters between the pins on the base, and a GY6.35, measuring 6.35 millimeters between the pins on the base. Just like the J type bulbs, a JC halogen shouldn't come in contact with bare skin since it can damage the bulb.

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    ...and if it does come in contact with skin, it should be cleaned with something like isopropanol and a lint-free cloth. The risk with touching a halogen bulb is that the bulb temperature is high enough for the salts in human sweat to catalyze devitrification of the glass that can lead to premature failure. Since halogens operate at elevated pressure, this means the bulb explodes.
    – J...
    Commented Nov 19, 2019 at 20:24
  • It seems there are more sizes than just those two.
    – Dan Jacobson
    Commented Aug 21, 2023 at 10:29

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