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I have a lamp that is rated at 60 Watts for an incandescent bulb with a disclaimer to use a 13 Watt bulb instead when using a CFL replacement. Do I really need to respect that disclaimer? Would not a 23 Watt CFL be just as safe to use? It still draws less power than a 60 Watt incandescent, right?

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ur 60W bulb..is it CFL or incandescent?? – Vineet Menon Nov 2 '11 at 10:49
I have no bulbs - I just have a "lamp", which I really meant to be a light fixture, not a bulb itself. – Ziplin Nov 14 '11 at 19:49
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The disclaimer does it say 'at most 13 watt CFL' or is it worded more as a suggestion? I'm betting it's a suggestion, and is intended to tell you how much CFL will give the same light as a 60 watt incandescent. – Michael Kohne Dec 5 '11 at 14:13

migrated from physics.stackexchange.com Nov 16 '11 at 18:36

4 Answers

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your this comment

Would not a 23 watt CFL be just as safe to use? It's still drawing less power than a 60 watt incandescent, right?

is correct.

The disclaimer probably would be for the light intensity...probably its a reading lamp, so higher intensity light can damage your eyes...

Mind you this is just a speculation!

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The disclaimer is for fire safety. – Chris Cudmore Nov 16 '11 at 21:33
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I picked this because I realized, that yes, this light is too damn bright for me to read by. Well speculated, Vineet! – Ziplin Dec 27 '11 at 22:20
60 Watt incandescent = approx 800 Lumen = 13-15 watt CFL So it's the recommended light intensity. – Fiasco Labs Dec 19 '12 at 23:10
up vote 8 down vote

As far as I know, the only risk at issue here is of overheating. The heat comes from two sources: the output and waste heat of the bulb, and from resistive heating of the lamp wires and switch and socket contacts. CFL bulbs draw less current and produce less heat for a given light output; however, they are far less tolerant of high temperatures!

Therefore, the rationale of the warning label may well be to warn that the fixture is not sufficiently ventilated for a CFL bulb above that power.

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CFL's seldom overheat!! You can even touch a CFL after say 10 hours of continuous operation! – Vineet Menon Nov 16 '11 at 5:25
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They don't get as hot to the touch, but they get very unhappy (as in "fail frequently after short lifespans) in spaces that allow them to heat up too much (with "too much" being much less than "burn your fingers" hot. – Brian Knoblauch Nov 16 '11 at 21:23
This is especially true if the bulb is enclosed in e.g. a recessed fixture, or pointing a direction other than upward (especially down). In such situations a CFL bulb could overheat and fail, smoke, or even catch fire. In the early days of CFLs you weren't supposed to put them in enclosed or recessed fixtures [which may still be true] or point them down at all. – Random832 Dec 7 '11 at 17:28
CFLs seldom overheat, but their ballasts sure are capable of going off in a powerful smell long before the design life noted on the packaging has been met. They're not for use in enclosed, unventilated lighting fixtures. I've had shorter lifespans than the incandescents they're supposed to replace under these operating conditions. – Fiasco Labs Dec 19 '12 at 23:06
up vote 6 down vote

The issue here is light output, specified in lumens. An incandescent bulb puts out about 15 lumens per watt, so a 60 Watt bulb will put out about 900 lumens of light. However, a CFC may put out 45 - 60 lumens per watt (3 - 4 times as much), depending on the design. They are simply a lot more efficient at converting electrical energy into light. Because of this, a 13 Watt CFC will put out the same amount of light as a 60 Watt incandescent bulb. Putting in a bigger CFC simply gives you a lot more light.

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up vote 2 down vote

I'm playing a bit fast and loose with the units here -- Watts are a measure of power, but the idea should be clear.

Typically, you find these ratings on the socket where there is likely to be a shade in use. The smaller the lamp, the more likely you are to use a small shade, and the closer the shade will be to the actual bulb. The warning is there so you don't set the shade on fire, or melt it. 90% of the power (watts) of a light bulb is emitted as heat. wikipedia. So, a 60 watt bulb emits 54 watts of heat, and 6 watts of light. A CFL uses less power for the same light by a factor of 3-4. meaning a 13 watt CFL will emit the same 6 watts of light -- giving off 7 watts of heat.

TLDR; The wattage rating is for fire safety, you could use a 60W CFL in the socket, if you could find one of appropriate size. The rating has nothing to do with the amount of light produced. Only heat.

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