Bulb limits on lamps - why much lower for fluorescent?

Angilion · 15 Oct 2012 at 07:27

This is niggling at me.

I've been looking at a few lamps and they all specify a limit of a 60W incandescent bulb or 11W fluorescent bulb.

I can understand why a lamp would be limited to, in this case, a 60W incandescent bulb.

But why would the same lamp be limited to an 11W fluorescent bulb? A 20W fluorescent bulb would still draw much less power and produce much less heat than a 60W incandescent bulb, so why is it too much for the lamp?

Hamish · 15 Oct 2012 at 07:33

probably not a limit; more likely a recommendation

mattyfez · 15 Oct 2012 at 07:47

Maybe due to physical size, the next size up 22w? Is quite a bit bigger, maybe to close to touching the lamp shade, or poking out too far which is probably against regulations?

ubersonic · 15 Oct 2012 at 08:01

IIRC a 60W incandescent and 11W fluorescent will have roughly the same light output, so sounds like its a recommendation.

Also on a UK 230v supply a 60w bulb will draw 5x the amps of 11w bulb, dunno if this is relevant though.

Angilion · 15 Oct 2012 at 08:22

mattyfez said:
Maybe due to physical size, the next size up 22w? Is quite a bit bigger, maybe to close to touching the lamp shade, or poking out too far which is probably against regulations?

That sounds plausible.

Meridian · 15 Oct 2012 at 08:34

Personally I suspect force of habit. Some low-level functionary was given the job of translating the output to the new-type bulbs, and did a straight conversion based on industry agreed figures on outputs. No-one cared to redo the work to find out what the actual safe limit was. Since it's based on heat output not causing a fire, not bulb size (in the vast majority of cases, anyway), the new figure is too low, but no-one can be bothered to fix it.

Mercenary Keyboard Warrior · 15 Oct 2012 at 12:08

Had this recently, ignored the low number for the fluorescent.

I replaced a 60watt incan with a 15watt fluoro, light fitting said same as yours, 11w max

Makes no sense. It wasnt closer really, infact was probably further away

pingwing · 15 Oct 2012 at 12:09

Sometimes its just sensible to accept the rules and follow them. Questioning them takes too much time to achieve anything useful.

Dr.EM · 15 Oct 2012 at 12:51

OP is quite right, it can't be because of dangerous heat output, but as others have suggested it may be due to supposedly equivalent light outputs or bulb sizes.

Those equivalent CFL outputs are somewhat off I think though, I'm using a 100W incandescent in this room as the extra heat output is useful for offsetting this being the coldest room in the house, hence it's actually not a waste of energy (it rarely is in British climate tbh)! I've never seen a CFL produce the same output or quality of light, I expect a lot of us have been using CFL for a while now, you may be surprised if you change back to see how much better the light is from incandescent!