# What is the heat output for different kinds of light?



## BatteryCharger (Dec 23, 2005)

Does anybody know the heat output for different types of lighting? I mean, a 60 watt incan bulb puts out alot more BTUs than a 60 watt fluorescent or 60 watts of HID...does anybody know the actual BTU/watt output of the different types of lighting?


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## Data (Dec 23, 2005)

If they were all consuming 60W they would all put out about the same amount of heat. However, the 60W fluorescent may actually be only consuming 20W. So it is only putting out 1/3 the heat as the others.

A good way to think about it is the power they are consuming is mostly all ending up as heat. Even the light that does not go out the window is ending up as heat in the room. On a very minor scale the other electromagnetic radiation that flies right through the wall is escaping the room too.


Cheers
Dave


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## BatteryCharger (Dec 23, 2005)

That would be impossible. The way lights like fluorescents and HID make more light from the same wattage is because less of the energy is turned into heat and more is turned into lumens.


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## asdalton (Jan 8, 2006)

1. Watts are a measure of power (energy per time)--electrical, mechanical, thermal, etc. Btu/hr is the counterpart in the English system, but by convention that unit is used only for thermal power. Sometimes you will see Btu/hr erroneously shortened to "Btu", which is actually a unit of energy and not power.

2. A 60-watt bulb, by definition, consumes 60 watts of electrical power. (As with many products, there may be differences between nominal product labeling and actual power consumption.) Those 60 watts have to go somewhere. More efficient lamps produce more lumens per watt, but all of that radiant energy eventually is absorbed by surfaces in the room and becomes thermalized. So it all ends up as heat, just not always right away.

3. Radio waves are a form of radiant energy that actually can escape from a house, but that is a small component of the total energy emission from a lamp.


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## BatteryCharger (Jan 22, 2006)

asdalton said:


> A 60-watt bulb, by definition, consumes 60 watts of electrical power. (As with many products, there may be differences between nominal product labeling and actual power consumption.) Those 60 watts have to go somewhere.



And the question is, how much of that 60 watts is turned into heat, how much is turned into light, and how much is turned into other, in different types of lighting?


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## brickbat (Jan 23, 2006)

It'd help to have a little background on your reason for asking. Since you originally asked about BTUs, one viewpoint is that practically all 60 W gets turned into heat, regardless of the lamp type. This is so since even the light that is generated gets absorbed somewhere and turned to heat...

The reason you can't find a simple watts-to-lumens theoretical conversion is that they are really units with different dimensions. (which is why the lumens per watt measure is correctly termed efficacy instead of efficiency...but that's another thread) It can be done at a given wavelength, but gets tougher for 'white' light.


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## jtr1962 (Jan 24, 2006)

BatteryCharger said:


> And the question is, how much of that 60 watts is turned into heat, how much is turned into light, and how much is turned into other, in different types of lighting?


Of course it varies greatly even for a given type of light but here are some ballpark figures in rough order of efficiency:

4 watt night light bulb: 2.5% light, 97.5% heat
100 watt incandescent: 9% light, 91% heat
1 watt Luxeon (45 lumens): 12% light, 88% heat
500 watt projector incandescent: 18% light, 82% heat
40 watt T-12 fluorescent (excluding ballast losses): 20% light, 80% heat
32 watt T-8 fluorescent (excluding ballast losses): 27% light, 73% heat
400 watt HID: 30% light, 70% heat
250 watt low-pressure sodium: 40% light, 60% heat
Cree XT-27 blue LED die: 42% light, 58% heat

Note that conversion efficiency figures cannot necessarily be correlated with lumens per watt due to the differing efficacies of the emitted spectrums. For example, if we could produce an incandescent light specturm with 100% efficiency we would only be at 200 lm/W but a white LED type spectrum might give us 300 to 400 lm/W. Also note that low-pressure sodium lamps emit entirely at one wavelength with a luminous efficacy of over 500 lm/W. I also didn't include "other" because as far as I know whatever isn't emitted as light is emitted as heat although small amounts of UV may escape the tubes of some discharge lamps.


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