Max Bulb Wattage in Enclosed Fixture?

In my home bathroom, one of the light fixtures is on the ceiling. One incandescent bulb screws in and hangs straight down and the cover is a glass "bowl" that completely encases the bulb and fixture.
I have never seen a wattage rating on any of the bult in fixtures in this house. I had been using a 100 watt bulb in this for the last few years. However, I seem to recall someone posted in here that if the bulb was completely encased, then it should never be more than a 60 watt bulb. Is that true?
I assume this is a heat issue? But is it more of a bulb life issue or a safety issue?
-- John

It is a heat/fire/safety issue.
Too much heat and no ventilation can cause a lot of heat build-up above the fixture. Place insulation above the fixture in the attic and it can get worse! I've seen old wiring above these fixtures where the insulation has cracked from the heat and there are bare wires in the box above the fixture.
So potential shock hazard and/or fire hazard. How about using a compact fluorescent which is more cool and also saves energy?
"John Ross" wrote in message
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CFLs generally don't take heat as well as incandescents, and many will cook themselves to death in this fixture. (Enclosed bathroom ceiling fixture) I would use only ones rated for recessed ceiling fixtures. The highest output one of these that I know of if the Philips SLS 23-watt non-dimmable. (The dimmable one was not rated for recessed ceiling fixtures last time I checked.)
- Don Klipstein ( snipped-for-privacy@misty.com)

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Hi John,
Most enclosed fixtures are rated for a maximum of 60-watts and in absence of any label, I would avoid using a 100-watt lamp. If you require the light output of a 100-watt lamp and would prefer to stick to an incandescent source, I might recommend one of the new high-efficiency incandescents from Philips. The one that provides the same amount of light as a standard 100-watt incandescent uses just 70-watts; granted, a little more than the 60-watt maximum, but pretty darn close. In addition to the 30-per cent reduction in energy use (and corresponding reduction in heat), these lamps last up to four times longer than a regular A19 incandescent. They're available at Home Depot.
For more information, see: http://www.nam.lighting.philips.com/us/consumer/hes/display.php?mode=1
Cheers, Paul

Paul M. Eldridge wrote:
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Thanks, I never heard of those. Might be useful for other locations. Have you used these? If so, can you tell the difference in the light from the regular ones?
-- John

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Hi John,
I haven't personally and likely won't because the fixtures in my home that use regular A19 lamps have all been converted to CFLs, or where the lamp is exposed, decorative (flame style) halogens.
To the naked eye, light quality should be pretty much indistinguishable from a standard soft white incandescent -- if anything, its slightly higher colour temperature should improve overall light quality. These lamps utilize an internal halogen capsule, so the tungsten filament runs a little hotter (2,900K) and, as a result, the light would appear slightly "whiter" than a standard soft white incandescent which generally fall closer to 2,700K.
For more information on these lamps, see:
http://www.nam.lighting.philips.com/us/pressroom/10-30-07a.php
and
http://www.nam.lighting.philips.com/us/ecatalog/halogen/pdf/p-5901.pdf
Cheers, Paul

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It's not true at all. Depending upon the size of the fixture, a single lamp fixture will typically take from 60 to 100 watt lamps. I would be more concerned with the insulation type of the house wiring than the wiring of the fixture. If your wiring is old rubber covered cloth, I would use the lowest wattage, preferably CF lamp, you can get. If it's 90 degree thermoplastic, I'd use whatever max is recommended by the manufacturer. Here is an example of a typical cheapo 100 watt fixture: http://www.lightingdirect.com/index.cfm/page/product:display/productId/K218/manufacturer/Kichler/categoryId/3838/finish/White
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Bah humbug, just use a compact flourescent and you'll be OK (since it only uses something like 23 watts for a 100 watt equivalent).

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There are some locations where CF lamps are inappropriate, and other locations where folks just don't care for the glaring light they emit

RBM wrote:
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http://www.lightingdirect.com/index.cfm/page/product:display/productId/K218/manufacturer/Kichler/categoryId/3838/finish/White
This house was built in 1960. It has the cloth covered Romex with no ground wire. I don't think there is "rubber" covering it (I think the cover is an off white color if that helps)? Would the type you are referring to have been in this time frame?
-- John

That would probably be cloth covered Romex with thermoplastic type "TW" conductors rated at 60 degrees. You don't want to get to much heat on these conductors, but they won't bake and crumble like cloth covered rubber.
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But then you move the wire and the plastic insulation cracks off. The worst fixtures I ever saw were the old circline fluorescents with the ballast right under the supply wiring.
Modern fixtures usually come with fiberglass insulation in the canopy to keep the heat away from the supply wiring. If your fixture doesn't have any you might want to add some.
RBM wrote:
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Besides the other good reasons posted here, keep in mind the design criteria for a consumer light fixture will call for a bottom of the line lamp socket. Typically , these will be rated for 60 W max, and the heat of larger lamps will deteriorate the socket plastic parts, the contacts will get limp and you will see it flicker. I have upgraded some fixtures that needed higher wattage lamps by using commercial sockets designed for display fixtures. Upgrading ventilation and wire is also part of the job. HTH
Joe

John Ross wrote:
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I have replaced the three 60-watt bulbs in my kitchen fixture of the same type with three 23-watt compact flourescents. You need to wear sunglasses in there now. It's great.
If I could've fit 40-watters in there, I would have.

snipped-for-privacy@rochester.rr.com wrote:
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I suspect the 23-watters in there are the highest wattage CFLs that will not overheat in that fixture.
- Don Klipstein ( snipped-for-privacy@misty.com)