# LED bulb surface temperature



## wcord (Jan 23, 2011)

Had a customer ask an interesting question.

If the fixture is rated for, lets say, a 60 watt bulb, could he use a 13 watt LED which is the equivalent of a 100 watt incandescent?

We know the restriction on the wattage is due to the heat radiating off the incandescent. And the heat is primarily centered around the glass.
Whereas, the heat off the LED is centered on the heat sink, not as large of an area as the glass.

Anyone have any information as to whether installing a larger LED would be a fire hazard?


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## PlugsAndLights (Jan 19, 2016)

wcord said:


> Had a customer ask an interesting question.
> 
> If the fixture is rated for, lets say, a 60 watt bulb, could he use a 13 watt LED which is the equivalent of a 100 watt incandescent?
> 
> ...


I'd say the fixture rating is for real watts (ie 13W) not equivalent watts
(ie 100W). So they could put a 200W equivalent in there if they wanted
to as it's only about 36 real watts......if it fit. 
P&L


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## daveEM (Nov 18, 2012)

I'm still looking for a LED bulb that can be put in an enclosed fixture.


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## macmikeman (Jan 23, 2007)

PlugsAndLights said:


> I'd say the fixture rating is for real watts (ie 13W) not equivalent watts
> (ie 100W). So they could put a 200W equivalent in there if they wanted
> to as it's only about 36 real watts......if it fit.
> P&L



I ain't buying that, but if you do it's wonderful, because I prefer you to be the test monkey on behalf of myself . Let us know how it works out please. Oh and thanks for your sacrifice and service to the public. I mean it :thumbsup:


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## Big John (May 23, 2010)

Heat is measured in power absorbed over time. Watts is a measurement of power, so the amount of wattage something consumes is directly related to how much heat it generates.

It's literally impossible for something using 13Wh of energy to put out more heat, or even the same heat, as something using 60Wh of energy.


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## macmikeman (Jan 23, 2007)

Big John said:


> Heat is measured in power absorbed over time. Watts is a measurement of power, so the amount of wattage something consumes is directly related to how much heat it generates.
> 
> It's literally impossible for something using 13Wh of energy to put out more heat, or even the same heat, as something using 60Wh of energy.


That's terrific. Now please explain scientifically how 50 watt halogen puck lights wont burn down a kitchen cabinet because after all it's only a 50 watt lamp.


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## Big John (May 23, 2010)

Halogen lights are hot because FEMA fills them with chemtrails.


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## HackWork (Oct 2, 2009)

Big John said:


> Heat is measured in power absorbed over time. Watts is a measurement of power, so the amount of wattage something consumes is directly related to how much heat it generates.
> 
> It's literally impossible for something using 13Wh of energy to put out more heat, or even the same heat, as something using 60Wh of energy.


What if the 13w device is much, much less efficient than the 60w device? 

What if, for example, the 13w device is putting only 1w towards it's intended purpose (let's say light) and 12 watt to heat, while the 60w device is putting 55w towards it's intended purpose and only 5w to heat?


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## Big John (May 23, 2010)

HackWork said:


> What if the 13w device is much, much less efficient than the 60w device...?


 The ratings are based on expected heat load from an incandescent bulb, and incandescents are fantastically inefficient: The average incandescent converts <5% of the power to light; they are space heaters that also happen to glow in the dark. So it's practically impossible to exceed the fixture thermal rating by accident.


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## HackWork (Oct 2, 2009)

Big John said:


> The ratings are based on expected heat load from an incandescent bulb, and incandescents are fantastically inefficient: The average incandescent converts <5% of the power to light; they are space heaters that also happen to glow in the dark. So it's practically impossible to exceed the fixture thermal rating by accident.


I have to admit, this is above my head.



> The ratings are based on expected heat load from an incandescent bulb, and incandescents are fantastically inefficient


The wattage ratings on bulbs (incan, CFL, or LED) are how much power they use, no? So I don't understand your above statement.

I'm still not understanding how a very efficient 13w device can't put out more heat than a super efficient 60w device.


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## Big John (May 23, 2010)

HackWork said:


> ...I'm still not understanding how a very efficient 13w device can't put out more heat than a super efficient 60w device.


 In theory it could. But incandescent bulbs are so inefficient that to make things simple we can pretend that all of their power rating gets turned directly into heat.

That means if you've got a fixture rated at 60W, then it is designed to tolerate 60Wh of heat energy continuously. So any other bulb that either
A) uses less power or 
B) uses the same power more efficiently 
will expose that fixture to less heat.


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## wildleg (Apr 12, 2009)

efficiency is an actual quantity, even though it is used in everyday language.


the efficiency of a mechanical/electrical device is usually defined as the percentage of work performed divided by the total energy used.

in the case of the incandescent bulb, the efficiency would be:

Watts of light energy/watts supplied on the circuit.

now, one could find the light energy by measuring, or more easily measure the amount of heat output along with the heat lost in the conductors (voltage drop).

so the Watts of light energy = Watts supplied - Heat loss of bulb - heat loss of conductor resistance.

and the efficiency would end up being something along the lines of what John said, or in other words, you would lose 80 to 95 percent of the energy supplied doing work other than that which was intended (ie. lighting).


hope that helps.


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## PlugsAndLights (Jan 19, 2016)

The numbers vary by brand etc but they're roughly like this:

Incandesent -> 2.5% eff -> [email protected]% -> 1.5W light and 58.5W heat
LED -> 10% eff -> [email protected]% -> 1.3W light and 11.7W heat 

While the location of the heat will be different between the two, 11.7W
of heat is very unlikely to cook the wires etc the way 58.5W will. 
@daveEM made a good point in post #3 re; enclosed fixtures. AFAIK, this 
is related to lamp life only, not overheating of wires etc.. 
P&L


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## Majewski (Jan 8, 2016)

PlugsAndLights said:


> I'd say the fixture rating is for real watts (ie 13W) not equivalent watts
> (ie 100W). So they could put a 200W equivalent in there if they wanted
> to as it's only about 36 real watts......if it fit.
> P&L


Lol..... sometimes my motto is "if it fits, I sticks".


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## MCasey (Dec 7, 2016)

Big John said:


> Heat is measured in power absorbed over time. Watts is a measurement of power, so the amount of wattage something consumes is directly related to how much heat it generates.
> 
> It's literally impossible for something using 13Wh of energy to put out more heat, or even the same heat, as something using 60Wh of energy.


Very much so, if not we'd have seen LED heater infomercials coming out the ears.


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## !Tom (Dec 8, 2013)

wcord said:


> Had a customer ask an interesting question.
> 
> If the fixture is rated for, lets say, a 60 watt bulb, could he use a 13 watt LED which is the equivalent of a 100 watt incandescent?
> 
> ...


Isn't that comparison of saying a 13W LED being the same as a 100W incandescent only equivalent in the amount of lumens it produces, not the amount of energy.


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## inetdog (Apr 13, 2016)

!Tom said:


> Isn't that comparison of saying a 13W LED being the same as a 100W incandescent only equivalent in the amount of lumens it produces, not the amount of energy.


Yes, and unlike the case of an incandescent bulb the color temperature of an LED is not tied to its thermal temperature. 

Sent from my XT1585 using Tapatalk


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## !Tom (Dec 8, 2013)

inetdog said:


> Yes, and unlike the case of an incandescent bulb the color temperature of an LED is not tied to its thermal temperature.
> 
> Sent from my XT1585 using Tapatalk


You mean you can't switch to cool lighting during the summer to beat the heat? :laughing:


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## inetdog (Apr 13, 2016)

!Tom said:


> You mean you can't switch to cool lighting during the summer to beat the heat? :laughing:


It might be subjectively more comfortable

BTW, I have one bathroom in my house that is not tied to the HVAC system.
I put in a heat lamp bulb in the can next to the shower for winter and replace with an LED trim each summer. Does that count?

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## !Tom (Dec 8, 2013)

inetdog said:


> It might be subjectively more comfortable
> 
> BTW, I have one bathroom in my house that is not tied to the HVAC system.
> I put in a heat lamp bulb in the can next to the shower for winter and replace with an LED trim each summer. Does that count?
> ...


Just use a red LED, same redness, less wattage.


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## inetdog (Apr 13, 2016)

!Tom said:


> Just use a red LED, same redness, less wattage.


Actually, it is a white heat lamp. Higher wattage. less IR absorption in the shell, and a reflector with good IR performance compared to a standard bulb. But still not as high CCT as the LED.

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