Why do LEDs generate heat?

[Max Demian]

Why, as the white is really just blue doped with a fluorescent pigment, and doesn't produce a continuous spectrum?

[Commander Kinsey]

I think the phosphor produces a wider spectrum than an LED? To make a nice white with just LEDs, perhaps we'd need several of them. Your eye might only pick up three wavelengths, but a lot of objects in the room may not reflect those specific three very well, so we need the inbetween ones aswell.

[Andy Burns]

It's more continuous than separate R,G & B peaks, there's a blue peak and then a broad green to red hump

[The Natural Philosopher]

Because the actual spectrum is broader

[AlexK]

Most neighbours don't have much long term inductive load anymore.

[AlexK]

More likely the capacitance effect you get with double insulated stuff.

[Commander Kinsey]

I don't see why it would have reduced. Inductive load is from motors - mowers, washing machines, vacuum cleaners, etc. This hasn't changed.

[Commander Kinsey]

Could be. Would that also cause the buzzing when earthed?

[Mark Lloyd]

I have a LED bulb (60W equivalent) in a lamp here. The bulb itself doesn't get hot like an incandescent bulb does. What gets hot is an area around the base.

[Commander Kinsey]

That irritates me, why don't you write "an LED"? How do you say "LED"? I say "Ell Eee Dee", not "Light Emitting Diode". So it needs an "an", not an "a".

60W? Are you a Klingon and love darkness? I use 100W and 150W bulbs only. And lots of them. My living room (7 metres by 4 metres) contains 13 90W bulbs.

Through the heatsink probably, most of the heat is generated by the LEDs, not the far more efficient power supply.

[AlexK]

It has anyway.

The type of motor used in those has tho. Far fewer of the original motors with a power factor problem now in domestic appliances.

[AlexK]

That's more likely to be due to a significant earth current when earthed. Easy to measure.

[Dave W]

If you plot voltage across the LED versus current through it, the curve is not linear like a resistor. At low voltage it hardly conducts, but at higher voltage it conducts a lot, and the curve flattens like a not very good zener diode, limiting the voltage.

Voltage times current equals watts i.e. heat plus a little light. Light has a power but it's miniscule. Complicated physics theory might explain how the light is produced and why so little of it, but we lesser mortals wouldn't be able to understand it.

[The Natural Philosopher]

No, it isnt.

Solar panels at midday work. Sunlight in the tropics at midday us around 1KW/sq m.

It isn in the case of LEDS quite a lot. IIRC 10% efficient or thereabouts.

the current knock electrons into higher orbits, as they fall back they emit photons.

Nobody understands anything completely

[Commander Kinsey]

For what reason Mr Speed? You ain't fooling me.

Ah, so you answered it here instead of up there where you interrupted. FFS.

[Commander Kinsey]

0.020mA per foot of lighting (they're 4.5W per foot). I don't call that significant and can't see how it would cause an audible vibration.

[Commander Kinsey]

It only limits it for a while, then you get smoke.

I always thought an incandescent bulb was 1% light, 99% heat. A fluorescent tube was 5% light, 95% heat. And an LED was 10% light, 90% heat.

As a ratio those are about right. 100W tungsten = 20W fluorescent = 10W LED.

But I've been told elsewhere that LEDs are 40% efficient.

[Mark Lloyd]

[snip]

"an LED" irritates me. I know the word is "light".

It also matters if the light source is in the right place, like from behind is good if you're reading or watching TV.

Some people think more light is always better. I remember working behind a TV (26-inch CRT console), where I could see OK. Then someone, trying to be helpful, turned on a nearby wall lamp. The effect of that is that the area behind the TV became completely BLACK.

[snip]

[Commander Kinsey]

But which would you say if you read the sentence out loud? Do you say the letters like me, or do you say the full words? I say "DVLA" not "Driver and Vehicle Licensing Authority"

I prefer the whole room to be evenly lit.

More light is better if the whole room is lit evenly. Which is why I prefer strip lights to point sources. Much better if you're soldering for example, you don't create shadows, as light can come to the workpiece from all angles, no matter where your body/head/hands/tools are.

[NY]

I think it is normal convention that an initialism that starts with a *vowel sound* takes "an", on the grounds of euphony: that in normal English, you never precede a word that starts with a vowel sound with "a".

Hence an apple, but a uniform. A hedge or a hotel or a historic event but an honourable occasion (H is sounded for the first three but silent for the last one). For some reason, it considered "better" to use "an" before hotel and historic, even though the H is sounded. That sounds as daft to my ears as "an spoon" - it's not a vowel sound so you use "a". I could understand if people pronounce hotel the French way, but it needs to be consistent: "an 'otel" or "a hotel".

As regards initialisms/abbreviations, you do get anomalies like "an LED" (ell-ee-dee) that starts with a consonant but "a UFO" (you-eff-oh) that starts with a vowel pronounced as a consonant.