Why don't dome light fixtures overheat ?

[Stephen Tashiro]

Why don't "dome" light fixtures overheat?

"Domes" are the type of fixture where there is no airspace between the ceiling and the dome shaped glass cover. I purchased one recently. It has a big sheet of insulation over the top of it, so not much heat is going to escape through the electrical box were the fixture is attached.

I plan to use LED bulbs in it, but I'm curious why heat isn't a problem in such fixtures when incandescent bulbs are used.

[Frederick Skelly]

Hi Stephen.
Hey, I'm not sure what the fixture you're using looks like and maybe you're already thinking about this concern..... But I'm thinking that just because the dome fixture doesnt overheat with incandescent bulbs, doesnt mean it's necessarily safe for LEDs. Are the bulbs you're going to use fairly small output? I ask, because the ones I bought last week (just regular lamp bulbs, 1600 lumens I think) said there was a hazard if used in a closed or too confined space. I'm certainly no expert and I defer to the guys who really are (Dan H, etc), but I wanted to raise it just in case it matters in your application.

Best regards,
Fred

[Stephen Tashiro]

Hi Stephen.
Hey, I'm not sure what the fixture you're using looks like

It's like the "flush mount" fixtures listed on this page from Sutherlands.https://sutherlands.com/c/Ceiling-Fi...s_market=false (I bought the fixture at the local Sutherlands Hardware.)

[Michael Weber]

Any stable heat source reaches equilibrium with its environment. In this case the glass dome, metal ect. is absorbing the heat and radiating it out to the room. You could increase the wattage of the bulb until the glove could not provide enough absorsion and, lacking a temperature overload device like in pot lights, it would overheat. Fixtures come with a maximum allowable wattage rating for that reason.

[Frederick Skelly]

Any stable heat source reaches equilibrium with its environment. In this case the glass dome, metal ect. is absorbing the heat and radiating it out to the room. You could increase the wattage of the bulb until the glove could not provide enough absorsion and, lacking a temperature overload device like in pot lights, it would overheat. Fixtures come with a maximum allowable wattage rating for that reason.

Yes, I agree with you. The thing that is different with LED bulbs is they are low wattage/high lumen. So it looks like - from the warnings - they can be within the rated "wattage" for a given fixture and still get too hot to be safely used in that fixture. I think that's why they warn against using the ones I bought in a closed fixture.

[Stephen Tashiro]

Fixtures come with a maximum allowable wattage rating for that reason.

Is system for making wattage ratings is up to date? - with respect to new types of light bulbs.

For example, a fixture with a 100 watt incandescent bulb in it may not get hot enough to damage parts of the fixture or the incandescent bulb, but what temperatures can LED bulbs stand ? And LED bulb of less than 100 watts might not make the fixture as hot, but it might get hot enough to damage the LED bulb, if LED bulbs are more sensitive to temperature than incandescent bulbs.

One would hope that a fixture rated for 100 watt incandescent bulb would be safe for an LED bulb of equivalent brightness, but less wattage. Is that a good rule of thumb ?

[Jerome Stanek]

In some older cars the dome light would melt the cover

[Ken Fitzgerald]

All the LEDs I have been installing produce MUCH less heat than the incandescent equivalent or larger incandescent bulb. I can actually grasp the LEDs replacement in a 6 bulb fixture in my bathroom but wouldn't grasp the 40 watt incandescent bulb in the same fixture. Gradually, I am replacing all the bulbs in my house with LEDs.

They produce so much more light with less wattage consumed.

2 years ago I had more insulation blown into the attic of our home. Last year as part of the kitchen remodel, I had all the old aluminum thermo-pane windows replaced with vinyl thermo-pane windows. Since last summer as an incandescent bulb burns out I am replacing it with an LED replacement. With the kitchen remodel we have 7 times as many lights (LED cans) in the kitchen providing much more light. Our total energy bill according to the utility company for the first 6 months of this year as compared to the same time period of the previous year has decreased 15%. I get a "Smiley face" now on my energy bill when compared to equivalent homes in the neighborhood.

[Stew Hagerty]

The problem isn't with the LED generating too much heat for the fixture. The problem is that LED's have some rather temperature sensitive electronics inside the bulb. A flush mount fixture has no way to eliminate heat build-up inside. If the bulbs are left on long enough the heat inside the fixture will overheat the electronics and reduce the lifespan of the bulb. This is typically not an issue until you get up to the 100w equivalent ones, as the smaller ones don't generate nearly as much heat. For that same reason, most 100w+ equivalent LED's are larger and incorporate a heat sink.

[Ken Fitzgerald]

Stew,

It's been my experience that the increased amount of light allows me to use a lower wattage bulb as recommended by the LED manufacturer. I get more light for less wattage and less heat.

I have a dome light in our hallway which was remodeled as part of the kitchen remodel last year. IIRC, the fixture has 2, 7.5 watt LEDs in it and that hallway is better lighted than when I was running 2, 60 watt incandescent bulbs.

There's no denying that LEDs cost more up front. I did have some premature failures a couple years ago. My wife and DIL bought a bunch of LEDs equivalent replacement bulbs when Costco had a 50% off sale 2 years ago. I am still gradually using those to replace the incandescent bulbs.

We have a 3-way lamps in our living room and bed room that we use for reading. The incandescent were burning out regularly and drew enough current to damage the sockets over time. I began replacing those last year and had one failure. The 3 way LEDs are terribly expensive ($21 IIRC) but they are lasting longer than their incandescent cousins.

[Tom M King]

The CREE bulbs won't last long in an enclosed fixture. It says on the box not to mix them with other types of lamps in an enclosed fixture, but I can tell you from experience that they don't last as long as incandescents in the same ceiling lights even with nothing but CREE led's in them. That also applies to fixtures that are mostly enclosed. So far, the cheaper LED's are proving to last longer, but still nothing like the claims. We have a drawer full of burned out CREE lamps from Home Depot. It did say to send them back with POP, but we haven't gotten around to it yet.

Still loving the CREE flashlight bulbs, but no more home bulbs for us.

[Stew Hagerty]

Stew,

It's been my experience that the increased amount of light allows me to use a lower wattage bulb as recommended by the LED manufacturer. I get more light for less wattage and less heat.

I have a dome light in our hallway which was remodeled as part of the kitchen remodel last year. IIRC, the fixture has 2, 7.5 watt LEDs in it and that hallway is better lighted than when I was running 2, 60 watt incandescent bulbs.

There's no denying that LEDs cost more up front. I did have some premature failures a couple years ago. My wife and DIL bought a bunch of LEDs equivalent replacement bulbs when Costco had a 50% off sale 2 years ago. I am still gradually using those to replace the incandescent bulbs.

We have a 3-way lamps in our living room and bed room that we use for reading. The incandescent were burning out regularly and drew enough current to damage the sockets over time. I began replacing those last year and had one failure. The 3 way LEDs are terribly expensive ($21 IIRC) but they are lasting longer than their incandescent cousins.

I understand the lower wattage issue completely Ken, but I think you misunderstood me. I said 100w "equivalent", In LED terms than means roughly 14.5w. However, all of the A19 14.5w LED's I have seen say right on the packaging NOT to put them in an enclosed fixture due to overheating. If you bump up to an A21 bulb, the heat level on them drops off, but they are approximately 25% larger than the A19 due to a larger heat-sink and are likely not be able to fit into an enclosed fixture.

[Frederick Skelly]

The problem isn't with the LED generating too much heat for the fixture. The problem is that LED's have some rather temperature sensitive electronics inside the bulb. A flush mount fixture has no way to eliminate heat build-up inside. If the bulbs are left on long enough the heat inside the fixture will overheat the electronics and reduce the lifespan of the bulb. This is typically not an issue until you get up to the 100w equivalent ones, as the smaller ones don't generate nearly as much heat. For that same reason, most 100w+ equivalent LED's are larger and incorporate a heat sink.

That makes sense. Thank you.

[Ken Fitzgerald]

Stew,

I do understand that the LEDs could be heat sensitive. For 40 years I troubleshot some pretty sophisticated equipment used in air traffic control centers and in hospital radiology departments. Heat and humidity problems were often difficult to troubleshoot. My profession got a lot easier once recording temperature instruments became available. It got even easier when the internet came along and the recording device (temperature, humidity and cryostat pressures) could send me an email or page me via a pager or cell phone to let me know an MRI magnet had a potential problem. Then I could dial in from home, troubleshoot, order parts or notify a customer they had a problem without ever going to the site.

The bulbs I have in the domed hall light are IIRC, 60 watt equivalent LEDs. I installed them near the end of last August when the contractors were finished with the kitchen remodel. They haven't failed yet. But, as they are in a domed hall light fixture, they don't get used as often or left on as long as other light fixtures might.

Beyond that, the brightness of the light that I see from LEDs is such, I can replace a 60 watt incandescent with a 40 watt equivalent LED and get an equivalent amount of light. I think it has to do with the color of the light being emitted.

I am merely stating I haven't experienced a problem. I am also not using 100 watt equivalent LEDs so the amount of heat they generate isn't the same.

I think LEDs are coming into their time as their reliability increases and prices come down due to a larger supply.

[Brian Elfert]

Cree makes some LED bulbs with no heat sinks called 4Flow. I just looked and the package I have for one doesn't say it cannot be in an enclosed fixture.