A science question

[likeafox]

Here's the question. Consider that you have two lamps, in a completely enclosed room. One is an incandescent bulb, the other is an array of LEDs. Both lamps use exactly the same amount of electricity. In this enclosed room, do the lamps both heat up the room the same amount? Or will one be more effective at heating up the room than the other?

Everybody knows LEDs are much more efficient than incandescent bulbs (by a matter of magnitude, infact). Thus, the LED produces almost no heat directly. But according to the laws of thermodynamics, energy can not be created or distroyed, only changed. In a theoretically enclosed space, the light produced can not be lost, only absorbed into the environment and changed. Since both lamps use the same amount of power, would the LED not create just as much heat in the end, though indirectly, by the produced light being absorbed by the environment and converted into heat?

That is assuming that the light is not converted into another type of energy. It could, for example, be converted into chemical energy through photosynthesis when coming in contact with a plant. But in a practical sense-- say in an empty room with brick walls and no windows-- would the resulting difference of generated heat between the LED lamp and incandescent lamp be negligible? In what other ways might the light energy be changed?

[klimt]

from what i remember of high school physics...

the incandescent bulb will always do much more to heat the air than the LEDs. Air is very bad at becoming warm from light passing through it, so an object has to be warmed up by the light first then transfer heat to the air. this is incredibly inefficient.

incandesent bulbs work on the same principle as your oven, only they're set up to create light, not just heat. so they heat up the bulb quickly, which then warms up the air.

the LED would have to use the process described in the first paragraph.

[Tai]

Paging Rymn

My take on this is, if it truely is a closed system and both use the same wattage than yeah both will heat up the house equally.

However, even if light is really efficient at getting across air, the energy has to degrade somewhere. And since heat is the destiny for all energy (lol entropy) alas for the LED lightbeam. LEDs are about 2-3 times more efficient at making light from elektricity than incandescents.

But yeah, LEDs get warm if you feed them 3 times the normal current. And 3 times as bright I'd imagine. Even if the LED was 100% efficient in converting to light, the light will degrade into heat as every air molecule sucks it in and burps it out, and the brick wall absorbs the rest.

But let a physicist tell you the real answer

[jent]

This is actually a lot more complex than you guys originally thought. It is important to note that LED's and incondecent bulbs do not give off the same kind of light. LED's only give off a very specific wave length of light, where as most other types of bulbs give off a spectrum with different levels of different spectrums. I know what your thinking, how do they have white LED's then since white is a combo of all colours. Well there is actually no such thing as a white LED, the LED is actually flashing very quickly between two colours to trick the eye.

So what do I mean by all this...well your comparing apples and oranges for one thing, the light given off by each device is in no ways equal. So it is hard to say which one is giving more 'light' because the LEDs will be giving TONS of light in only one or two wavelengths, where the normal bulbs will be giving tons of light in a more normal spectrum.

Putting that aside if you look at the amount of 'light' given off and not care about the spectrum then LEDs will easily win on light output vs energy used. And that is why they produce lots less heat, they don't waste as much. The issue is you can't really over power much LED's they are an all on, or all off thing, no levels really between if you don't want to damage the diode. So in order to get more light you must add more LED's. Which can make things very expensive for high light requirements.

Hopefully this answered your question better instead of just babbling on

[Doc Sigma]

Threads like this make me feel like a

[gforce422]

I found this on the internet which elaborates on Jent's post very nicely.

An LED is a monochromatic light source, emitting light energy within a very narrow wavelength band. In contrast, an incandescent light source emits energy in a very wide wavelength band, including the visible light spectrum, infrared, ultraviolet and heat.

The diagram below illustrates both a red LED and an incandescent light bulb in terms of wavelength emission as a percentage of relative intensity. The red LED features a very narrow wavelength band that contains only red light between 620nm ~ 675nm. The light from the red LED is rich and vibrant in color, a direct result of the narrow wavelength band. The incandescent lamp on the other hand is emitting the entire band of the visible spectrum as well as parts of the non-visible spectrum. Most people are familiar with how hot a light bulb may become during operation by accidentally burning a finger. The high temperature is a direct result of energy emission in the form of heat, which is inefficient. Since the LED emits light energy in a narrow wavelength band, heat emission is not an issue, making the LED a very efficient light source that remains cool to the touch when operating.



The image below is an illustration of how color mediums affect monochromatic light. A red plastic lens is covering red, white, blue and yellow LEDs. The different LED colors illuminate through the lens and appear in their original color, making the red plastic glow blue and yellow in some spots. For signage applications it is important to match the color of the sign face with the color of the LED to optimize lighting performance and color.


(That is really fascinating to me. Maybe it's just because I work at a lighting store... )

Oh, and to answer likafox's question, I think the answer is no. Incandescent bulbs produce WAY more heat than LED's, after all, 95% of the electricity that goes into a lightbulb is wasted as heat. The filament is acting like a resistor, and heating up white hot, which is what creates the light. My thought is that, regardless of light being converted to heat by the LED, the incandescent bulb is going to produce vast amounts more heat than the LED will by means of thermodynamics. Just my thoughts.

[Tom Flapwell]

For future science questions, you might try the "FreeFall" forum or the "21st Century Fox" forum. Both those comics are frequented by science buffs.

[Arloest]

monochromatic

OOHHHHHH

WHO WILL GIVE IN FIRSSSTT

THE BODY OR THE LASSSHHHH

MONOCHROMATIC STTAAINNNSS

OHHHHHHH

WHO WILL GIVE IN FIRRSSTT

THE LEADER OR THE FAKKEEE

MONOCHROMATIC STTTAIINNSS!!!!


That's all I can properly contribute to this topic.

[datherman]

As the answer has probably already been explained properly, I submit this animation in place of any actual content (click for larger, more bandwidth-sucking version):



EDIT: longer version available here:


Sorry about the UNREGISTERED HYPERCAM thing, couldn't really help it.

[Softpaw]

This isn't really my arena, but I noticed that LAF's original setup didn't involve a single LED, but rather an array of LED consuming the same amount of electricity as the incandescent bulb. Given the small amount of electricity needed by LEDs, that's a huge number of them, likely over a hundred depending on the brightness of the LEDs, and the amount of power used by the incandescent bulb. Does that make a difference?

[KJ Fellie]

This isn't really my arena, but I noticed that LAF's original setup didn't involve a single LED, but rather an array of LED consuming the same amount of electricity as the incandescent bulb. Given the small amount of electricity needed by LEDs, that's a huge number of them, likely over a hundred depending on the brightness of the LEDs, and the amount of power used by the incandescent bulb. Does that make a difference?

It is because the incandescent light works by heating up to white hot in order to produce light that it is both hotter and less efficient. I think gforce422 did a good job of explaining it, and probably a little more fully than I would have.

EDIT: I think a better way for me to say what I mean is to explain that a larger percentage of energy from the incandescent is being put out as heat, and for the LED a larger percentage of energy is being put out as light.

[nickspoon]

It is because the incandescent light works by heating up to white hot in order to produce light that it is both hotter and less efficient. I think gforce422 did a good job of explaining it, and probably a little more fully than I would have.

EDIT: I think a better way for me to say what I mean is to explain that a larger percentage of energy from the incandescent is being put out as heat, and for the LED a larger percentage of energy is being put out as light.

But eventually all the energy put in to the incandescent bulb and the array of LEDs (which is exactly the same amount of energy) must become heat (and thus exactly the same amount of heat). The LEDs will produce far more light but they both ought to produce the same amount of heat in the end.

[KJ Fellie]

It is because the incandescent light works by heating up to white hot in order to produce light that it is both hotter and less efficient. I think gforce422 did a good job of explaining it, and probably a little more fully than I would have.

EDIT: I think a better way for me to say what I mean is to explain that a larger percentage of energy from the incandescent is being put out as heat, and for the LED a larger percentage of energy is being put out as light.

But eventually all the energy put in to the incandescent bulb and the array of LEDs (which is exactly the same amount of energy) must become heat (and thus exactly the same amount of heat). The LEDs will produce far more light but they both ought to produce the same amount of heat in the end.

Yes, that may be true. I'd forgotten about that.