CFLs, incandescent bulbs, and lamp safety

I recent bought a torchiere-type floor lamp at Target. This is the first time I’ve bought a lamp since compact fluorescent bulbs became common. When I looked at the safety rating for the sockets, they specifically said “Use with MAX 60 W Type A lamp or use MAX 15 W CFL lamp.”

Why are these maximum wattages different? I always thought that the main reason for wattage maximums in light fixtures was to make sure that you didn’t have too much heat buildup and start a fire, and therefore that you could safely swap an incandescent bulb for a (much brighter) CFL bulb of equal wattage if you wanted to. Is there some other limitation I’m unaware of? Or did the Target designers just not want people plugging extra-bright bulbs into their lamp and throwing off the feng shui?

I can’t recall where the dividing line is, but lower wattage incandescent bulbs have a different shape to the base of the bulb where the contact on the bottom is. This was done so bulb sockets in small lamps won’t work with a bulb with too high wattage. If CFLs follow that pattern, that may be the reason. Or the Feng Shui thing. One of those two should be the answer.

My first thought is that it’s a mistake.
I routinely put 20,24, or even higher wattage CFLs in fixtures designed for 60W incandescents, and I’ve never had a problem. I suppose it’s possible that the fixture has poor air circulation, and they are worried about the CFL ballast overheating, but that seems a bit far-fetched.

the electronics of the CFL produces heat and needs to have ventilation. the larger the CFL the more heat and larger the base which may not have ventilation enough. the light output of both bulbs is the same.

I suspect it’s because incandescent bulbs can be operated at a much higher temperature than CFL. A 60-watt CFL in this lamp shouldn’t damage the lamp, because as you point out, it produces no more heat than a 60-watt incandescent bulb. But the 60-watt CFL may damage itself if used in this lamp.

Good point, the heat generated by CFLs concentrates in the base, while incandescents generate most of the heat in the filament, which can radiate from the top of the bulb, unobstructed in a torchiere type lamp.

Also, aside from any technical reasons, the lamp might have been designed based on incandescent bulbs, and a simple conversion was used to specify the CFL size.

CFL produce heat in the base which may be located in the fixture housing in an area with less ventilation. an incandescent bulb produces heat where the filament is which may be more exposed.

tripolar and i had the same thought are nearly the same time.

Did a little light bulb go one over your head? That’s what happened to me. Actually, you had the idea first in post #4, and both our followups were obvious derivatives.

It could also be that since the 15 W CF is said to be equivalent to a 60 W IC bulb that someone just equated the 2 in the sticker, more likely if the lamp was made outside the US in a country with cheap labor, such as China.

Yup, CFLs have issues with heat that incandescents don’t. In particular, CFLs are usually designed with the cheapest components possible in order to compete on price with their predecessors, and cheaper components have a lower maximum temperature rating. Particularly prone to failure is the electrolytic capacitor after the input rectifier, which should ideally be rated to the industrial spec 105 deg. C, but are invariably the cheaper 85 deg. C types.

You won’t find this in big print on the side of the CFL packaging, but the majority of these bulbs aren’t designed for mounting base-upwards, as the electronics in the base will get too hot and the lifetime will be reduced. The life expectancy figures quoted by the OEMs - and hardly ever realised in the home - are with the bulb mounted base-down in an uplighter or wall sconce. And with minimal on/off cycling, as this also reduces their lifetime.

I recently bought a reissue Anglepoise 1227, a 75 year old classic design. Except that the new one has been designed around a 15 W CFL (it doesn’t give a spec for an incandescent). As CFLs give a horrible light spectrum (and the curly glass types without a secondary glass envelope also give out nasty UV) I replaced it with a 60 W halogen bulb, to find that the weight distribution was designed for the heavier CFL, so I’ve had to add counterweights to rebalance it. Not happy.

Don’t believe the equivalent incandescent wattage the CFL OEMs quote, it’s demonstrably not true. If you want the usable light output equivalent of a 60 W incandescent, pick one that claims 75 W equivalence.

Not that I disagree with you, but cite?
I haven’t tested CFL light output, but it seems to me that the company wouldn’t claim light equivilence without some backup.

As for the nasty UV, turns out that “UVA leak highest from incandescent and halogen bulbs, and UVB leak highest from CFL.” No bulbs produce measurable UVA or UVB at distances of 100 cm or more.

Bless! Could I interest you in some magic beans? Less facetiously, it’s because there are currently no regulatory standards regarding the claims to optical output levels of light bulbs, so OEMs can massage the figures a little. The human eye is optimised for the spectral output of the sun, a broad output that is hard enough to duplicate with incandescents. Fluorescent lights have spectra that are more a series of spikes, and while this gives the illusion of white light it’s much more difficult to read or do detailed work under. And of course the colour rendering is way off. Cite. However, the incandescent output equivalence figure of a CFL can be bumped up by judiciously weighted averages that favour the CFl spectrum, or even cheekily just measuring the peaks. BBC - “Why eco-light bulbs aren’t what they seem”.

This is an increasing problem as the choice of lightbulb types increases, and eventually legislation will catch up, probably with an optical power criteria that defines a broadband spectrum and weighted to the response of the human eye. This was thankfully included as one of the design requirements for the US Dept of Energy’s L-Prize, a $10M bung for the first company that can come up with a decent low energy bulb. To date the US DoE haven’t paid out.

As for the UV output, I’d say 100 cm (about a yard) is not a very practical safe distance. If I’m doing fiddly work then my face is often inches from my desk lamp, where the UV output from a curly CFL is enough to give one a slight tan. They have also been known to fade pigments in carpets and upholstery, but on the plus side will gives any houseplants in the area a bit of a boost. The enclosed bulb CFLs have secondary envelopes that attenuate the UV to genuinely negligible levels.

LED lightbulb technologies will eventually mature to overcome the spectrum and UV problems of CFLs, but they still suffer from issues with heat damage to the electronics.