Many LED bulbs say 'not for use in enclosed fixtures. This is usually attributed to heat buildup. However, someone pointed out that a cell-phone charger, delivering a comparable 12W, typically consists of a virtually-closed small plastic enclosure.
If heat is such a problem for an LED bulb in a much larger enclosed fixture, why don’t phone chargers overheat even worse?
When the charger is delivering 12W power to the phone, most of this power is being stored in the battery in the phone, not dissipated as heat. Whereas a 12W LED “bulb” will be dissipating almost all of the 12W as heat.
The incandescent bulb radiated most of that heat with the visible light. This is about where the LED bulb gets hot and either, as wolfman just pointed out, that the enclosed fixture will make the base of the bulb overheat, or that the fixture might not be able to handle that hot a bulb base.
They’re not worried about the fixture, they’re worried about the diode(s.). The hotter an LED is while operating, the shorter it’s life will be. There’s a reason most of the mass of an LED light bulb is heat sink.
I’ve replaced 6 200w halogen rs7 bulbs with 15 watt led’s at our community entrance wall. The landscape type floodlight fixtures are sealed. The LED units are supposed to last 50000 hours (how they determine that, I don’t know) but my failure rate more closely resembles 10000 hours.
Not so good, right? But, vs. the halogen, over the life of these $8.00 led units, they save us close to $175 in power costs for each fixture, about a $1000 a year. No, they aren’t as bright, but they do the job of lighting up the entryway wall and sign just fine.
I imagine that the rather modest heat buildup in the fixtures does effect the life of the led’s circuitry. Any ideas how to radiate this heat away effectively and efficiently?
Modern LED bulbs shaped like old-fashioned incandescent bulbs are designed to go into enclosed fixtures and replace the older bulbs. You shouldn’t continue to assume that first generation limitations still apply. These aren’t special LEDs either. Any basic Home Depot or equivalent sell them.
I think the other factor is, the LED emitter itself is much smaller and much hotter than the rest of the “bulb” and fixture. When the whole fixture gets warm, the LED emitter gets dangerously hot. And it’s the LED emitter that’s damaged by heat.
When a phone gets warm, the battery isn’t that much warmer than the rest of the phone.
Got a cite for this? Fixtures typically include a label that says something like “max power X watts,” where X is some number, typically 60 or higher. CFLs rarely have wattage that high; a 43-watt CFL has a lumen equivalent of a 150-watt incandescent, so most people won’t even be using a CFL that powerful. It’s hard to imagine that a 43-watt CFL could damage a fixture rated for a 60-watts or greater.
That said, CFLs in poorly ventilated fixtures (or mounted upside-down, such that natural convection doesn’t provide adequate air flow) can overcook the electronics in their own base, resulting in shortened CFL life. Likewise with LED bulbs.
I don’t have a cite to link, but a two-bulb enclosed fixture I installed in the spring stated, both in the installation instructions and several labels/tags on the fixture itself, that the fixture was rated for two 60w incandescent bulbs, *or * two 13w (60w incan. equivalent) CFL bulbs.
Does it “nexto to convect” ? The fixture will conduct, and radiate infrared.
The air around the outside of the fixture can also conduct heat into the air, and then thats where convection acts to spread the heat (to the rest of the ceiling), to keep temperature down.
This might be a case of “Try it and see”, because who’s going to obtain and use R ratings of the fixture’s materials to figure out the operating temperature ?
It would only take a small hole to let air flow to keep 15 Watts convecting away…
Put a hole in a safe place at the fixture (where it doesn’t expose the mains power…)
When a fixture has a maximum wattage rating it’s to protect the fixture from melting, burning, shorting out, or burning down your house, not to protect the bulb. An incandescent bulb doesn’t care how hot or cold it is, so it will function just fine even if it produces so much heat that it ultimately destroys the fixture around it. CFL or LED bulbs may not produce enough heat to damage such fixtures or their surroundings, but because of the design of the fixture they can still burn themselves up because the heat damages their electronic circuitboards and ballasts. This is usually the case in “base up” situations like recessed cans or hanging pendant lights with enclosed shades, whereas “base down” situations like table lamps tend to be ok.
This arrangement can cause extra problems with CFL bulbs because the mercury in them can condense and settle to the bottom, causing longer warmup times and less light at power-on than in a base down situation where the mercury would settle on the cathodes and be vaporized much more quickly. That’s also why CFLs have trouble in cold temperatures, they can’t keep the mercury vaporized. Enclosed fixtures help for cold applications, though not for startup, but for something like an outdoor fixture it then runs the risk of burning up in warm weather.