A 60W-equivalent LED lamp uses 6-8W of energy. Assuming it converts roughly the same amount of energy (1.25W) into light, the remaining 4.75-6.75W needs to be converted to heat. That's about as much thermal dissipation as a low-end laptop CPU, but concentrated in a much smaller area and with a much less effective cooling system (it doesn't even have a fan). 85 degrees sounds about right.
[Edit] Still, 85 degrees is nothing compared to the extreme temperatures that a filament in a regular light bulb experiences. It's only a problem because the LED chips aren't made of carbon or tungsten like filaments are.
[1] https://en.wikipedia.org/wiki/Incandescent_light_bulb#Effica...
This isn't relevant to your argument, but that actually isn't true, that figure is about 6~8 percent.
* The "luminous efficiency" as commonly reported is just the lumen/W luminous efficacy divided by the peak value of 683lm/W. The value of 683lm/W is the peak of human eye sensitivity curve and occurs at 555nm. The only light source that can achieve 100% "efficiency" by that measure is a 100%-efficient radiator that emits monochromatic 555nm (bright green) light, the best a perfect white light source can do is about 37%. (see [1])
* That "perfect white light source" would be a 100%-efficient radiator emulating the Sun spectrum bandlimited to visible light (zero infrared, uv and no other losses).
* It's possible to make a light source that appears white to human eye and is more efficient than that by emitting mostly at wavelengths the human eye is more sensitive to, and emitting less at wavelengths it's less sensitive to. That's part of the reason why manufacturers often offer CFLs with high efficiency but poor color rendering and lower efficiency but higher color rendering. (And don't get me started on the color rendering index.)
* That definition of "efficiency" is obviously not what most people think it is when they hear that word (useful work / total work spent), some prefer to call it "luminous coefficient". But it's not all lies, it was defined that way because it's easy to compute and understand and because this is the value of interest if e.g. you're making a LCD backlight or if you're designing an interior lighting setup.
[i thought that was obvious - are you trolling?]
In terms of energy efficiency, CFLs are halfway between incandescent bulbs and LEDs. So the same comparison holds, only the differences are less extreme.
60W-equivalent CFLs use 13-15W of energy. That's approx. 1.25W into light (because the amount of light is more or less the same in all cases) and the remainder (11.75-13.75W) into heat. That's why CFL lamps get rather warm after a while. Very bright CFLs often have slots in the base for ventilation [1].
You just don't notice it as much because:
1) The heat source of CFLs is much larger than LEDs, so the average temperature is lower even though the total amount of heat is higher.
2) With all those coils and folds, CFLs have a larger surface area than most other types of lamps, so they cool easily.
[1] https://en.wikipedia.org/wiki/File:Compact_fluorescent_light...
That isn't true. LEDs are equivalent to CFLs in energy efficiency. The only LEDs that are more efficient are either lying to you (they claim the light is more directed so it "counts" as more, and they uprate the bulb), or they have worse color accuracy so you are not comparing equivalent bulbs.
> The heat source of CFLs is much larger than LEDs, so the average temperature is lower even though the total amount of heat is higher.
No. The heat source is not larger - it's in a different location, it's in the bulb part and it emits infrared light and is sent into the room. With LEDs the heat is made in the base and stays there.
> With all those coils and folds, CFLs have a larger surface area than most other types of lamps, so they cool easily.
That doesn't explain why an incandescent that makes 6 times as much heat can manage, but an LED can't. It's not the cooling of the bulb, it's the type of heat - incandescents and CFLs make their heat in the form of infrared light that is sent into the room.
Let's exclude lying vendors.
Worse color accuracy is annoying for those who care, but as far as total energy output is concerned, it shouldn't matter. A watt is a watt no matter what frequency it is radiated at.
> The heat source is not larger - it's in a different location, it's in the bulb part
Sure. And the bulb of a typical CFL is hundreds of times larger than the die of an LED.
> That doesn't explain why an incandescent that makes 6 times as much heat can manage, but an LED can't.
As I mentioned in the great-great-grandparent comment, glass tubes (CFLs) and tungsten wires (incandescent lamps) are much less sensitive to heat than tiny pieces of delicate electronics are. 85'C is child's play to glass and tungsten but deathly to silicon.
> incandescents and CFLs make their heat in the form of infrared light that is sent into the room.
The "sent into the room" part is definitely correct. LEDs overheat more easily because the heat is generated and trapped in the base. But even if you dangled a bare LED in mid-air, I doubt you could make it as cool as a CFL because the heat source is concentrated in such a small area. I'd also be surprised if those LEDs didn't generate a lot of infrared ratiation.
Ah, but if you are willing to have poor color accuracy then CFLs should be allowed that as well, and if you do that then their energy efficiency is better than an LED.
> glass tubes (CFLs) and tungsten wires (incandescent lamps) are much less sensitive to heat than tiny pieces of delicate electronics are
CFLs have switching power supplies in the base that don't like heat either. It's not just a glass tube. But I'm willing to accept that they can handle heat better than an LED emitter. (And I'm pretty sure it's just the emitter with the problem - it's certainly possible to make "delicate electronics" that can handle heat.)
the whole discussion above is concerned with the relative amounts radiated in visible and infra-red....
LEDs and CFLs are about equally efficient, but CFLs produce their heat on the bulb, and LEDs produce their heat in the base.
So CFLs (and incandescents) send their heat out into the room, which cools the bulb. LEDs keep all the heat inside which is a huge problem for them.
Personally I think bulb replacement LEDs are a dead end, and instead you should look for dedicated LEDs fixtures.
Edit to your edit: The amount of heat is actually quite small in comparison to a CFL. The temperature they're talking about is the die temperature. LED dies are tiny, so even though they can reach high temperatures, there's much less heat (waste energy) generated.
I have a 60W bulb I run through a dimmer that is in its 4th year. It is a nightlight for the kid's room so is never really turned off.
Filament resistance goes up because it is evaporating, heat goes up because the filament increases in resistance.
Higher overall resistance connected to the same voltage produces less current draw and therefore less heat. It's just Ohm's law.
The filament doesn't thin out uniformly, it tends to develop localized hotspots which leads to accelerated, localized evaporation. Eventually it breaks.
I have a 60W bulb I run through a dimmer that is in its 4th year.
You can make an incandescent bulb last an arbitrarily long time if you're willing to sacrifice efficiency by running the filament cooler. A dimmed-down 60W bulb may produce the light of a 5W nightlight bulb but use far more than 5W.
The Centennial Light Bulb has lasted a long time, not because it's never turned off, but because it's absolute shit as a light source. The filament stays cool and as a result its both terribly dim and terribly inefficient.
I didn't say heat didn't degrade incandescents, I said LEDs are much more heavily degraded when they're over their heat capacity.
The reason is due to the balance between heat generated and heat dissipated into the environment.
The bulb could convert 99% of the input electrical energy into light, and only 1% into heat. So for a 100W bulb, that would be only 1 watt of heat.
But if the heat dissipation system (i.e., the cooling system) can only dissipate 1/2 watt of heat into the environment over the same time span that the bulb is creating 1 watt of heat, the excess 1/2 watt of undissipated heat will build up over time, making the housing hot to the touch.
A CFL has a much larger volume to produce that heat, and a much larger surface area to radiate it; and even if it got very hot it wouldn't care that much. A LED is a tiny speck of semiconductor that bears the brunt of a lot of energy, and it's not rated for operating at high temperature.
It's like normal sunlight warming up the palm of your hand versus sunlight focused to a point by a palm-size loupe - it's the same total energy, but one is nice and warm whereas the other can cause serious damage.
They are not more efficient than CFLs. It is interesting that you think they are - I guess the marketing is working.
Now, you might come across some LEDs that on the surface appear to be more efficient, but actually they are misleading you. Those efficient LEDs have worse color accuracy than CFLs, so you are not comparing equivalent products.
LEDs do have room to improve, so they may get more efficient than CFLs, but they are not there yet.
The problem with LEDs, is you need a metal radiator positioned to not block the light. In a recessed fixture, the heat can get trapped.
edit: how can they be more efficient than cfls if they get hotter? how are the cooler cfls wasting energy? you can't just "lose" energy - it has to go somewhere. and normally for losses, it's heat.