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i'm confused. how can they be efficient if they get hot? are they less efficient than the coiled tubes? if so, why are they an improvement? edit: how can th

i'm confused. how can they be efficient if they get hot? are they less efficient than the coiled tubes? if so, why are they an improvement? 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.

benjamincburns 13y ago
They're more efficient, not perfectly efficient. 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.
- masklinn 13y ago
  And more problematically, heat severely degrades them (an incandescent bulb will also get extremely hot — as everybody who tried changing a just-blown bulb will know — but for the most part the heat will not significantly degrade it and lower its life expectancy)
  - yardie 13y ago
    Heat does degrade incandescents. The filament eventually vaporizes and as it gets closer to the end of its life it reaches thermal runaway in a split second. Filament resistance goes up because it is evaporating, heat goes up because the filament increases in resistance. 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.
    - masklinn 13y ago
      > Heat does degrade incandescents. I didn't say heat didn't degrade incandescents, I said LEDs are much more heavily degraded when they're over their heat capacity.
    - Lagged2Death 13y ago
      Heat is the way incandescents work. If they didn't get hot, they wouldn't make any light. Heat "degrades" them only in the sense that heating them (i.e., turning them on) eventually uses them up. The filament reaches temperatures of 2,000+ degrees C a fraction of a second after it's turned on; the type of fixture the bulb is in won't change the filament temperature much. 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. http://www.centennialbulb.org/ http://www.centennialbulb.org/
sean13013 13y ago
The parts that generate the lion's share of heat in an LED bulb are tiny tiny tiny, and so they can get very hot with much less energy. They generally have chunky heatsinks, but still you can only draw heat away from a point the size of a head of a pin so fast.
kijin 13y ago
A regular light bulb converts about 2% of its energy input into light, and 98% into heat. For a 60W light bulb, about 1.25W is converted into light and 58.75W into heat [1]. It's incredibly inefficient, and the filament can reach temperatures of over 3000K. (Ever wonder why CCFL lamps have their colors expressed as temperatures like 2900K? That's the actual temperature of a filament with the same color.) 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#Efficacy.2C_efficiency.2C_and_environmental_impact https://en.wikipedia.org/wiki/Incandescent_light_bulb#Effica...
- andrewcooke 13y ago
  i'm not comparing LEDs with incadescent bulbs, i'm comparing them with the coiled tubes - cfls. these things - http://en.wikipedia.org/wiki/Compact_fluorescent_lamp http://en.wikipedia.org/wiki/Compact_fluorescent_lamp [i thought that was obvious - are you trolling?]
  - kijin 13y ago
    I was just trying to explain how even an "efficient" lamp can overheat. Sorry I overlooked the CFL. 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_bulbs_105W_36W_11W.jpg https://en.wikipedia.org/wiki/File:Compact_fluorescent_light...
ars 13y ago
> how can they be more efficient than cfls 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.
jcampbell1 13y ago
CFL's also get hot, but the heat is on the coiled glass tube, so the heat and light radiate from the same place. Because the coil is the radiator, they ventilate heat naturally. In order to trap the heat in a CFL, you would need to design a fixture that doesn't let light out. 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.
Florin_Andrei 13y ago
They don't get "hotter" overall. The problem with LEDs is that most of that waste heat is produced in a tiny element - the actual LED chip - which is difficult to cool down because you can't surround it completely with heat sinks. The meager heat sinks you can put on the back of the chip are not so well connected thermally with the environment. 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.
pwg 13y ago
> i'm confused. how can they be efficient if they get hot? 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.

benjamincburns 13y ago

They're more efficient, not perfectly efficient. 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.

masklinn 13y ago
And more problematically, heat severely degrades them (an incandescent bulb will also get extremely hot — as everybody who tried changing a just-blown bulb will know — but for the most part the heat will not significantly degrade it and lower its life expectancy)
- yardie 13y ago
  Heat does degrade incandescents. The filament eventually vaporizes and as it gets closer to the end of its life it reaches thermal runaway in a split second. Filament resistance goes up because it is evaporating, heat goes up because the filament increases in resistance. 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.
  - masklinn 13y ago
    > Heat does degrade incandescents. I didn't say heat didn't degrade incandescents, I said LEDs are much more heavily degraded when they're over their heat capacity.
  - Lagged2Death 13y ago
    Heat is the way incandescents work. If they didn't get hot, they wouldn't make any light. Heat "degrades" them only in the sense that heating them (i.e., turning them on) eventually uses them up. The filament reaches temperatures of 2,000+ degrees C a fraction of a second after it's turned on; the type of fixture the bulb is in won't change the filament temperature much. 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. http://www.centennialbulb.org/ http://www.centennialbulb.org/

sean13013 13y ago

The parts that generate the lion's share of heat in an LED bulb are tiny tiny tiny, and so they can get very hot with much less energy. They generally have chunky heatsinks, but still you can only draw heat away from a point the size of a head of a pin so fast.

kijin 13y ago

A regular light bulb converts about 2% of its energy input into light, and 98% into heat. For a 60W light bulb, about 1.25W is converted into light and 58.75W into heat [1]. It's incredibly inefficient, and the filament can reach temperatures of over 3000K. (Ever wonder why CCFL lamps have their colors expressed as temperatures like 2900K? That's the actual temperature of a filament with the same color.) 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#Efficacy.2C_efficiency.2C_and_environmental_impact https://en.wikipedia.org/wiki/Incandescent_light_bulb#Effica...

andrewcooke 13y ago
i'm not comparing LEDs with incadescent bulbs, i'm comparing them with the coiled tubes - cfls. these things - http://en.wikipedia.org/wiki/Compact_fluorescent_lamp http://en.wikipedia.org/wiki/Compact_fluorescent_lamp [i thought that was obvious - are you trolling?]
- kijin 13y ago
  I was just trying to explain how even an "efficient" lamp can overheat. Sorry I overlooked the CFL. 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_bulbs_105W_36W_11W.jpg https://en.wikipedia.org/wiki/File:Compact_fluorescent_light...

ars 13y ago

> how can they be more efficient than cfls 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.

jcampbell1 13y ago

CFL's also get hot, but the heat is on the coiled glass tube, so the heat and light radiate from the same place. Because the coil is the radiator, they ventilate heat naturally. In order to trap the heat in a CFL, you would need to design a fixture that doesn't let light out. 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.

Florin_Andrei 13y ago

They don't get "hotter" overall. The problem with LEDs is that most of that waste heat is produced in a tiny element - the actual LED chip - which is difficult to cool down because you can't surround it completely with heat sinks. The meager heat sinks you can put on the back of the chip are not so well connected thermally with the environment. 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.

pwg 13y ago

> i'm confused. how can they be efficient if they get hot? 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.