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Comment by moffkalast | Hacker News Reader

Everyone lauds LEDs for being super energy efficient, but the reality is that they really aren't. It's just that they are being compared to even worse light sources that were so bad at efficiency it's hard to really grasp how much they sucked.

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LEDs are super efficient, household LED bulbs retrofit for e14/e27 are just a terrible example of overdriven ones with bad lifetime. That has very little to do w/ properly constant current (not over) driven LEDs. (Edit overdriven - higher heat output and worse efficacy)

The max efficacy woulod be 683 lm/w. Blue LEDs can reach 1/3 of the theoretical maximum.

The lifetime is pretty good when driven correctly to be sure, I was just talking about raw efficiency. Underdrive a led as much as you want, but you'll still lose half of your energy to waste heat. The heat will just be spread out more and be less noticeable on each chip.

Like, I'm sure we can agree high power LEDs have gigantic heatsinks and fans for other reasons than cosmetic.

Is there a more efficient way of producing light? Because I don't know of any.

The one that's the most neglected is natural lighting. Light pipes, solar collectors, and microprism window treatments are all available.

The second thing is white paint. You need less outdoor lighting if the built environment absorbs less light.

This does not solve the problem of filling city centers with huge company logos, adverts, signs for casinos or night clubs.

You're going to need very long light pipes to use natural lighting for your digital signage at night. Are you really sure that's a better option?

It's the most efficient option we have, but that doesn't mean it's good.

In the 1800s the steam engine was the most efficient way of producing work from heat, but that still didn't make it objectively efficient.

I read a neat article recently that talked about the "Dubai Lamp". They're lightbulbs that Philips makes for Dubai that are twice as efficient as their standard LED bulbs. The difference is simple: LEDs are more efficient when run at lower power, so by increasing the number of LED elements in the bulbs and reducing the voltage across them you get 600 lumens for 3 W. For reference, California requires lightbulbs to operate at 80 lumens per watt or higher.

https://hackaday.com/2021/01/17/leds-from-dubai-the-royal-li...

Looks like they're bringing this idea to the rest of the world:

https://www.lighting.philips.co.uk/consumer/p/led-bulb/87195...

LEDs can light a medium-sized room with <5W. That's incredibly energy efficient.

Not when you consider that it's still heating the room with 3 of those watts.

If you asked me to build a house and I threw away more than half of the bricks you'd call me crazy. But when it comes to leds it's called "incredible efficiency". It's only efficient in comparison to the other options, not in any objective sense.

“Efficient” is a relative comparison. Any absolute threshold would be arbitrary anyway

Not really. Converting all the energy to work would be 100% efficiency, converting none of it would be 0%. It's an absolute measure.

Now sure there are subcategories where 100% efficiency is the maximum theoretical efficiency (like the carnot cycle limit of 37% for heat engines), but that's already misleading info if not specified.

You provide no points to refute my statement. Being bounded between 0% and 100% is irrelevant, unless you think only 100% efficient is not inefficient - which would be absurd due to the impossibility of obtaining an “efficient” label.

If they are so inefficient then where does the wasted energy go?

The wasted energy as per usual - heat/entropy. It's just that LEDs are the best we have.

Where it always goes, waste heat. In the case of LEDs, about 50% to 60% of the power draw escapes as heat. Of course, incandescents are much worse.

70% near heat would the very very efficient blue leds, properly driven and all. below that, i.e. 50-60 is just theoretically impossible.

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