This is a very rare bulb. It works under 220 volts, so it barely glows under 125v, which was the voltage I used when I took the picture of it lit. The person who sold me this bulb suggested that it "was used in old time Street Cars (Trolley Car) of by-gone days" (like those used in San Francisco, California). I have my doubts about this because its filament is not designed to absorb vibrations. It is impossible to hold this bulb without causing its filament to wobble a lot. There is a sticker that says "16" but I don't think it refers to 16 candlepower, because this bulb has some features that did not exist when the lamp rating was changed from candlepower to watts. For example, the lead-in wires are made of dumet wire instead of platinum, and the bulb itself doesn't look like it was hand-blown. Quite a mysterious bulb. It is also interesting to note that this bulb was manufactured with little care. There is very little carbon paste on the center filament anchor, and the stem is bent. The evacuation tip is much thinner and longer than usual, thus making it more vulnerable to breakage. Looks like it was manufactured in a hurry! I suspect that this bulb was manufactured by NALCO (though not because of the low quality).