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Comment by thanksgiving | Hacker News Reader

I thought the question was limited to a "solid state"[0] computer processor.

There is no "useful work" moving large things on a computer processor. In this context, 100% of the energy consumed by a computer processor is heat, right? At least I think that is the working assumption when we build CPU cooling. If a processor consumes 15W of electrically power, we better have some way to move this 15W of heat away from the processor, right?

I have another question, for a light bulb, is this still the case? I guess for a candle or an incandescent light bulb, the question is moot but as we have more and more efficient lights like the "cool" LED lights, if the light source consumes 15W of electricity, do we need 15W of cooling?

[0] not a technical term

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I don't think the question was in the context of computers or even electronics in general, as the original claim cited ("70 percent of the world's power production ends up as waste heat") was certainly not restricted to computing.

In the context of CPUs, yes, the heat produced is equal to the input power. However this is not at all true for light bulbs, for motors, for battery chargers, etc. A light bulb in particular transforms some of the electrical energy into heat, but some of it into emitted light.

Even in incandescent bulbs, some the electricity gets turned into heat, raising the temperature of the filament, but past some point, the temperature no longer increases and all the extra energy gets converted into light. That is, if you were to submerge an incandescent light bulb in a large quantity of water and leave it on for 10 minutes, you'd get cooler water than if you submerged just the filament (ignoring the possible shortcircuits): if the temperature of the filament is kept below the point where it emits light, than all the electrocity goes into heat; but if it starts emitting light, then some of the energy escapes and doesn't heat the water.

The electromagnetic radiation still turns to waste heat.

Not necessarily, it can also turn to motion or to electricity or to chemical processes or to other things. For example, if you're using the light bulbs to light plants, it gets turned to sugar, not to heat.

I googled LED light efficiency what percentage of electricity becomes heat and looks like only about 20% of the input is wasted as heat?

So a 15W LED light would only need 3W of cooling? It feels even more ridiculous when we put the numbers like this... There is no excuse for LED lights to not have adequate cooling or for them to fail because of overheating...

> This means that about 80 percent of the electrical energy is converted to light, while 20 percent is lost and converted into other forms of energy such as heat.

Light bulbs are build to break and be replaced, as far as I understand we could have eternal light bulbs but that’s not in the interest of light bulb makers.

That same logic might still apply for modern light solutions like LEDs. I have a more expensive LED bar which is build on top of aluminium to disperse the heat.

Did you have heard about the Dubai Lamp? It’s basically a very efficient longlife LED which they only sell in UAE.

The Dubai Lamp is produced by Phillips, and is about 3x more efficient than typical LED bulbs -- normally 9w for 60w equivalent vs 3w. Their rated life is 25,000 hours, which is 2.5x longer than a typical 10,000 hour led.

They are damn impressive, but not "forever".

https://www.mea.lighting.philips.com/consumer/dubai-lamp

In the case of computers it turns to waste heat and whatever is radiated away is not usable energy and is essentially waste heat. Computers are basically devices for converting useful energy into waste radiation.

Agreed, in computers all of the input power becomes waste heat.

One small exception may be microntollers that use PWM to emit a signal through an antenna, or to drive a motor. I think in that case some of the energy becomes radio waves (which may never be absorbed entirely so they may not become heat) or motion in the motor.

'Useful' signal also comes out in the form of photons from the monitor.

Monitors have an external power source, I have never heard of a monitor being powered by signal coming from the CPU or GPU. That is, the control signal coming from the CPU/GPU doesn't become light, it merely helps decide what light a separate circuit might emit.

That's still radiation which turns to heat.

You are correct. All the electron motion in a CPU turns to waste heat or electromagnetic radiation which eventually becomes waste heat.

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