This is a very unusual bulb. It is designed for 220 volts, so under the 125 volts I used to light it up, it barely glows. 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, USA). I wouldn't be so sure about this, because this filament design is clearly not optimal for a harsh environment with a lot of vibration, like in a trolley car. In fact, this is one of the most wobbly, unstable filaments I've seen in a bulb. There is a sticker that says "16", which presumably stands for 16 candlepower, however this bulb has some features that were adopted after lamp ratings had already been changed from candlepower to watts. For example, the lead-in wires are made of dumet wire instead of platinum, and the bulb itself looks like it was mold-blown versus hand-blown. Quite a mysterious bulb. As a side note, this bulb seems to have been made with little care. There is very little carbon paste on the center filament anchor, and the stem is quite noticeably bent to a side. The evacuation tip is much thinner and longer than usual, and thus seems more vulnerable to breakage than usual. Definitely looks like it was manufactured in a hurry.