Hot light fixture spheres

[meirman]

Will drilling holes at the top of an otherwise sealed sphere encourage air circulation and make a light bulb run cooler?

I have a lot of light fixtures that use spherical glass globes to cover the bulb. There is no air circulation from inside the sphere to outside, and if I put in a high wattage bulb, it burns out quickly, I think.

One is a "chandlier", at least it hangs from the ceiling with a chain, with a glass globe 8 inches in diameter with a 4 inch opening at the top. Because it is not closely attached to the ceiling, I could drill holes in the metal part at the top, without weakening it. But if all the holes are at the top, would that make it run any cooler?

This fixture has a dimmer, and I'd like to use a 150 or 200 watt bulb, running it at 70 watt brightness most of the time.

(The other fixtures use a 6 inch glass sphere with a 3 inch opening, and they say not to use more than 60 watts. I don't know what max was recommended for the chandelier.)

Meirman

-- If emailing, please let me know whether or not you are posting the same letter. Change domain to erols.com, if necessary.

[Joseph Meehan]

You can not user lamps of a higher wattage than recommended in any fixture safely, even after drilling holes. Not may fixtures call for 150 -

200 W lamps. Find out what it called for (often printed somewhere on the fixture) and stay within that limit. Change fixtures if needed. BTW if the maximum wattage indication has been burned off the fixture, that should tell you something.

[nicksanspam]

Then again, warm air rises. You might measure the globe temp with no holes and the max recommended wattage, then drill the holes and turn up the dimmer until the globe temp rises to the original value.

Nick

[Ross Mac]

If you need more light, use florescent bulbs. They will give you about 3 times the light at the same wattage and won't exceed the rating of the fixture......Ross

[Joseph Meehan]

You also will need to measure the temperature at the socket, it does not rely on air temperature as a major issue, and the wires under it and other areas. If you want to find out if it is really safe, have the UL do the test.

[nicksanspam]

I don't think so. Just aim an IR thermometer at the globe. Basic heatflow. If it's the same before and after, the socket will be close to the same...

Riiiight :-)

Nick

[Phisherman]

[nicksanspam]

In a chandelier? :-)

Nick

[Joseph Meehan]

Personally I doubt it. The metal of the socket is physically connected with metal (usually a good conductor of heat) directly to the heat source, (the filament). I doubt if measuring the glass envelope is going to properly measure the problem.

I might suggest that since it appears the OP would like to be able to have both bright lights and be able to dim them, that maybe what he should do is that his opportunity to add additional light creatively rather than just over power the existing fixture.

[Joseph Meehan]

Yes, especially if it happens to be located under a washing machine or some such thing.

[BARRY MARTIN]

• Meirman:

M Will drilling holes at the top of an otherwise sealed sphere M encourage air circulation and make a light bulb run cooler?

M I have a lot of light fixtures that use spherical glass globes to M cover the bulb. There is no air circulation from inside the M sphere to outside, and if I put in a high wattage bulb, it burns M out quickly, I think.

M One is a "chandlier", at least it hangs from the ceiling with a M chain, with a glass globe 8 inches in diameter with a 4 inch M opening at the top. Because it is not closely attached to the M ceiling, I could drill holes in the metal part at the top, M without weakening it. But if all the holes are at the top, would M that make it run any cooler?

M This fixture has a dimmer, and I'd like to use a 150 or 200 watt M bulb, running it at 70 watt brightness most of the time.

Don't know the answer to your specific question -- it sounds semi-logical additional ventilation would cool the bulb better, but then the filament is running white-hot so the bulb, socket, etc., should be designed to operate at this hot temperature.

My concern is your proposal to use a 150 or 200 watt bulb. Is the fixture designed for a bulb of this wattage? Many sockets have a lable indicating the maximum wattage. It might be a good idea to replace the socket with one designed for the higher wattage.

.. Without electricity we would still be in the dark ages.

--- MultiMail/Win32 v0.46 þ wcECHO 4.2 ÷ The Safe BBS þ Bettendorf, IA 563-359-1971 þ * RelayNet(tm): CamCat (#3041): Telnet: bbs.camcat.com

[Joseph Meehan]

I suggest you ask your local fire department what they think of that idea.

Remember that the filament (the source of all the heat) is directly connected to the socket with metal (great heat transfer). The socket is going to get a lot of that heat. Cooling around the glass envelope is not going to do much for the socket. There is a good deal of poor conductor (air) between the filament and the glass. Your additional cooling air is going to only come into play removing the heat that has made it post the poor conducting air in the lamp and through the glass.

[Matt]

This is the reason that I put all of my bulbs in the freezer while they are lit. Safety first - that's my motto.

[Don Klipstein]

If convection within the globe is greater (airspeed is higher), the socket will be hotter - maybe not by much. You need to verify temperatures of everything not being any hotter than when "used as directed".

Now for another bad case: Suppose the chance of a fire starting is not completely perfectly zero in the worst case of "using as dirceted". So you do some usage other than "as directed" and verify no parts get any hotter but a fire starts anyway. Now you have what I fear is the liability problem of a fire starting from electrical equipment being used "other than as directed".

- Don Klipstein ( [e-mail])