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When shopping for lamps recently, I've noticed that the sticker on the socket says something along the lines of "To reduce risk of fire, use maximum 60 watt incandescent or 13 watt compact fluorescent." My question is, why does the maximum wattage vary for different types of bulbs? Shouldn't the socket be able to handle 60 watts, no matter what is drawing it?

I've searched on the Internet, and although the question has been asked before on various websites, most of it seems to be uninformed speculation, or people who don't even understand the question. (Hence why I decided to ask a forum of electrical engineers.) The best answer I've been able to find is that it's because the power factor of a CFL is significantly less than 1. That makes sense to me. So it seems like a "60 watt incandescent" socket is really a "60 VA" socket.

However, even if the power factor of the CFL is 0.5 (and my impression is that it's usually more like 0.6), then a "60 watt incandescent" socket should still be able to use up to a 30 watt CFL safely.

So, why does the socket say only a 13 watt CFL is safe? How does the manufacturer calculate this? Is there something else that needs to be taken into consideration besides power factor?

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The problem isn't the current the socket can handle, it's the heat. There is some very good informations here about CFL safety and so on.

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