Why do LEDs generate heat? (2025 Update)

That picture is from a 9 LED light that runs on 3 AAA batteries, Those are all over the place, usually in a drop bin or near the cash register at a hardware place..

In the case of power formulas E = Electromotive Force. AKA volts.

They don't sell small LED torches there that use 3 AAA cells? I am not even sure how a 2 cell light would work with a LED.

Sounds more like a religion than physics:

"The fate of the universe The Second Law also predicts the end of the universe, according to Boston University. "It implies that the universe will end in a ‘heat death’ in which everything is at the same temperature. This is the ultimate level of disorder; if everything is at the same temperature, no work can be done, and all the energy will end up as the random motion of atoms and molecules.”

All the second law states is you cannot decrease entropy. Nothing says you can't leave it the same, or 99.99999% the same.

Alkaline batteries? Perhaps by chance they managed to find a certain number of batteries and LEDs that matched precisely. Although I find it hard to believe that any AA battery has sufficient internal resistance to regulate current. I'm thinking if you changed it to use slightly different battery chemistry, with a fractionally higher voltage or lower internal resistance, the LEDs would soon die.

In the UK we use P=IV and P=iR^2.

E can be used for an electric field, but it should have an arrow above it, and it's in volts per meter, not power or energy.

Power invertor. Any decent torch (like my cycle lamp and my head torch I use to go hillwalking - which use one or two (doesn't matter which, they're in parallel) Li Ion batteries at 4.2V) converts the battery voltage electronically into the correct voltage and current for the LED(s). The cheapest torch I saw used 3 D cell batteries (a large torch) and a resistor.

So, do you use NiMH or alkaline in your LED torch? One would cause a dramatically different light output, or death of the LED.

Electromotive force is one of the few things often referred to by a unit of measure (voltage) rather than the name of the thing itself.

I don't know how to explain it very well, but perfection (as in 100%) is not a part of this reality.

Also a pop group.

Perhaps, but we still use V to indicate it in a formula. I've never seen it written as E. All symbols are unique, and E is for Energy.

Perhaps, but we can often get close to it. Think of the power supply in your computer. Good ones are 90% efficient. A modern condensing gas boiler is up to 95%. Motors constructed to meet NEMA Design B that are over 125hp must be at least 92.4% efficient. LEDs are pathetic in comparison.

Most do take 3 cells. I have one brighter LED light that uses 4 cells.

I described a little keychain light which used lithium cells, which have a cell voltage of about 3v each, so 6v for the two.

I have seen a LED on one (1.5v) cell, using a voltage multiplier chip.

Generational thing, I think. When I learned it the formula was E and now it's V. It's like when I learned it a girl was she and now a girl is he, she, they, zir, or whatever other else they want to be.

It may depend on where you are.

In the US it seems that V and E are used almost interchangeable. The oldest text book I have at hand (1947) uses E to represent voltage in the formulas. In my text books from around 1970 one uses V and one uses E for voltage. Most other more modern references use E for voltage in formulas and talking about values of tubes and other components.

It is pointless to say one is correct and the other is not.

Just as years ago when someone said cycles, it was understood it was usually cycles per second , which Hertz was assigned about 30 or 40 years ago. I am not going to dig out the date. That will be left for the students.

I wasn't aware they'd changed them, I guess you're talking about before SI units - does the USA have those or is it just a European thing? It was invented by the French after all.

It's like when I learned it a girl was she and now a girl is he,

Anything non-specific I call "it".

Dunno but I can tell you the ones with 3 AAA cells have the LEDs connected directly to the battery array with nothing but a switch in between and you can jumper out the switch with no ill effects so there is no resistor in there.

Maybe you just need some pictures if they don't sell them there. I have 3 different styles right here on the table next to me. Two have 9 LEDS, one has one big LED. They all use the same battery carrier with

This would be an example, similar to the one I took the picture of disassembled.

Alkaline or garden variety carbon zinc work fine. Just better life out of the alkaline

I can see why you people think lighting is a significant part of your electric bill. I have one 48" fluorescent luminaire in the kitchen that provides all the light I need for the kitchen, dining room and living room most of the time. With LED tubes that is about 26 watts. I have a task light by each chair if we are reading or something but they are usually off since we read on an electronic device most of the time these days. The rest of the lights are on motion detectors and only come on when we are there. (inside or out)

Bloody hell, they still make those? I got some on Ebay about 8 years ago for someone else who wanted a cheap torch for camping. I never looked inside. We have slightly more modern devices here now.

If you're referring to the ones you just linked to at Ace Hardware, I stuck NiMH in them and it seemed to work ok. Lower voltage but also lower internal resistance I guess. Maybe ultra bright LEDs aren't as fussy as the older ones. The original little 5mm red indicator LEDs would die very quickly without a current limiter.

You should have seen it with tungsten. Mind you in winter the wasted power heats the house. Although with gas heating, heating with electric is 3 times more expensive. We also have considerably more expensive electricity than most of America.

Not sure what you mean - is that one light for all three rooms? Or 3 of the same kind? And what are the room sizes?

So 260 watt equivalent. Mind you when I were a lad, we only had a 100W tungsten for every 16 square metres of room, and that seemed ok. Although it was irritating when you tried to do something fiddly, hence messing about with extra lamps. I prefer to just have the whole room bright all the time, so it's always easy to see, no matter what you're doing. It seems natural to me to make it as bright as it would be if you were out on a sunny day - more cheerful for a start.

I can't stand those, I can never get used to dragging my finger across a surface, it feels horrible and unnatural. I like a keyboard and mouse.

All my lights are. They work for pets too. If I see the kitchen light come on when I'm in here, I know somebody's up to something.