Ask LiveJournal Electrician: light fixture maximum wattage?

[randomness]

We have this old swing-arm lamp that takes three position bulbs. The socket is stamped 250W 250V, but I can't tell if it's just describing the socket or if the wiring in the lamp itself is rated for 250W.

Most modern swing-arm lamps I've seen have a tag that says they're limited to 150W. I figured I'd ask around before I put a 250 watt bulb in it and started a fire. :)

Anyone have any thoughts?

Comments

[rmd.livejournal.com]

that is likely just the socket.

[r-ness.livejournal.com]

Yeah, I was afraid of that.

[jendaviswilson.livejournal.com]

If it came assembled and the whole thing has a UL stamp, 250 is fine. But seriously, 250 is blinding and super hot! 100 should be sufficient for lighting a large area brightly. Use a CFL anyway, and you won't have an issue.

[r-ness.livejournal.com]

The socket has a UL stamp on it, but it may have been installed later.

Currently I have a 8/26/18W CF in it, but we need to do some fine work and throw some more light. I've seen what a 300W incandescent can produce, and the max on the 3 way CF I've seen is a lumen rating somewhere around what a 150W incandescent produces, so I'm looking around at all my options.

Thus far I've examined some high wattage 3 way halogens as well as CFs and incandescents.

Thanks!

[awfief.livejournal.com]

You can't start a fire with a higher watt bulb. If the socket sends 150W to a 250W bulb, you get a 150W light. That's how things like "dimmer switches" work -- they send less power to the bulb. The problem is you're going to start a fire because a 250W bulb is incredibly hot at full power. Can you even find a household 250W bulb that's not a flood light?

[r-ness.livejournal.com]

Actually, I was concerned about drawing more power through the wiring of the lamp. There are

There are 300W bulbs available for normal as well as mogul bases in the standard shape. There are a couple of 100/200/300W three way bulbs for both size sockets, although as they're too high wattage for the socket I'm not really considering them. There are also 50/200/250W three way bulbs available for standard screw-in bases, which are the bulbs I'm looking at.

Heat isn't a problem right now, actually; the fixture is base-down and if it helps to heat the room it's all to the good. :)

If there were a three-way CF that put out 2500-3000 lumens at max output, that would be nice, and it would probably be less than 50W at max output--I found a 60W single power that does 4000 lumens or so--but there isn't.

[gravitrue.livejournal.com]

Wires are resistors. They waste some of the power that goes through them as heat. The thinner the wire, the more it will heat up given the same amount of power going through it. A heavy load will try to suck more power through. Suck too much power through and things can catch fire, or simply melt off the insulation and cause shock hazards.
A standard light socket does not magically stop power at some wattage cutoff, it starts heating up. Of course, it might start melting from the bulb's heat first, which also isn't going to improve its safety any.

A dimmer, on the other hand, does magically stop the power at a given cutoff; most dimmers work by switching the light on and off really fast.

[chain saw with a magician (from livejournal.com)]

The stamp is ambiguous and could apply only to the socket. I have quite commonly seen such lamps with a sticker on the inside of the cone giving a much lower power rating than what the socket says.

You can draw your own conclusions from the gauge of the wiring. A table with some opinions on reasonable limits is here:

http://www.powerstream.com/Wire_Size.htm

From this, to support a 250W (~2.1 A) bulb, the wiring should be no thinner than 18 gauge. 18 gauge is common for lamp wire, so check, but it's likely to pass.

I guess that just leaves the stuff near the bulb itself as a potential problem. Unless some of it's made of plastic, it should be OK. If there's a plastic switch or something, that might be the limiting factor, and I have no easy suggestions for computing that limit.

[r-ness.livejournal.com]

Yeah, thanks for the helpful sanity check. I was looking for some indication of things to look for, and you've pretty much given me the answer I'd wanted.

[tfarrell.livejournal.com]

I think a 250 watt bulb is almost unbearably bright and you'd probably be more comfortable with less brightness. I also think 250 watts will run up your electricity bill, so even if you want that much brightness, you might be happier with something with the same light output but better energy efficiency, and that would likely mean a bulb under 150 watts of actual usage anyway.

[r-ness.livejournal.com]

This is why I'm looking for a three-way bulb for the three-way socket. The bulb will probably be run at its low power output normally, and only be run at high at particular times.

There are lots of three way bulbs. What is currently in the socket is, as I mentioned above, a three-way CF with a 26W maximum. I doubt it ever produced more than 1800 lumens. I'm looking for something brighter.

My baseline here is a fixture I have in CT which has two 42W CFs (around 2600 lumens each) and a 60W halogen (around 850 lumens) for a total of just over 6000 lumens. It's a nice amount of light, although when the halogen burns out I'll be swapping in another CF of equal or greater wattage, which should get the thing up over 7500 lumens.

A couple of the 50/200/250W three-way bulbs max out at 3955 lumens, which even from a point source isn't that bright, although I recognize it'll be warm. There's a 70/170/240W which maxes out at 3600, which might do.

What I'm really really looking for is a three-way CF that does something like 20/40/60W, which would put out around 3500 lumens at the max rating and be no problem for the wiring, but no one seems to want to build a three-way CF that bright. There's a 60W CF (3500 lumens), but it's single-brightness. Also it's $45.

The brightest three-way CF I've seen is a 22/33/55W, but it's a big fat circle and only puts out 2700 lumens. And it's $36. If it were cheaper I might pick it up as a retro statement; I used to have one in my room as a kid, but it's a little expensive and clunky to get as decoration.

Ultimately, I'll probably pick up the 70/170/240W or the 50/200/250W--neither of which costs more than a few bucks--if I can be sure the wiring won't fail. But I'm still looking at the switch.

And now I've probably written more about light bulbs than you ever wanted to read.

[twannger.livejournal.com]

Unless someone has rewired the lamp with a new socket, the stamp refers to the maximum possible bulb for the entire unit. Anything less won't be a problem.