LEDs vs. Lightbulbs

zymano writes "www.technologyreview.com has this nice article on LEDs vs lightbulbs" Follows the exploits of one Shuji Nakamura, the same man who brought you the practical violet laser.

Comments

I have a solid state LED flashlight

[jmccay]

I have a DORCY solid state LED Flashlight--actually, I have two. I liked it so much I bought it twice (one for home and one for my car). It works great. It doesn't difuse as badly as normal flashlights so it can shine further. Walmart seems to have stopped carrying it, but I got my second one at Sears for about $13.00 (no sales tax).

Crank flashlights and LEDs

[wowbagger]

I've a friend who works for Coleman (he's one of their webmonkeys, let's give him a heart attack by putting some "referrer=http://slashdot.org"'s in his logs).

He gets plenty of fun stuff from work. One of the things they have is a little crank powered flashlight that uses a Brinkman style little incand.

It will run for a fair length of time on the batteries, but I have to wonder how much longer it would run with an LED.

Perhaps next generation....

efficacy versus efficiency

[Michael.Forman]

This article, like most articles that tout LEDs as a replacement for light bulbs, confuses efficacy and efficiency.

Luminous efficacy is defined as the power of radiated visible light (visible luminous flux) divided by the dissipated electrical power. Given in lumens per watt, efficacy provides a useful means of comparing which source provides the most useful illumination for a given power.

Efficiency on the other hand is defined as the power of radiated visible light (visible luminous flux) divided by the power of all radiated light (total luminous flux). Ideally given as a unit-less ratio, efficiency provides the ratio of useful light to wasted light and does not necessarily correlate with efficacy. It is possible to have simultaneously high efficiency and low efficacy.

The question of why LEDs haven't already replaced all lights can be answered quickly by comparing the efficacy of different sources of light. All numbers below are approximate.

Filament light: 10 lm/W
White LED: 20 lm/W
Halogen light: 25 lm/W
Red LED: 40 lm/W
Florescent light: 100 lm/W
Sodium light: 150 lm/W
It can be seen why red LEDs have replaced halogen bulbs with red filters in stop lights -- red LEDs have a much higher efficacy. Note that the efficacy of LEDs are still well below that of florescent lights. If you feel frustration in seeing how far LED technology still has to go to compete with the boring lighting technologies of yesteryear, assuage your sorrows in the knowledge that you can save billions in energy costs right now, simply by switching to florescent lighting.

Michael.

Re:efficacy versus efficiency

[kriston]

Certain overnight radio shows tout the LED flashlights as being more efficient than incandescent or incandescent halogen. This is patently false. The LED lamps are more durable, but most do not use any more or any less energy than the equivalent incandescent or incandescent halogen at the same wattage (and efficacy).

The trend of changing traffic signals to use LED lamps is a question of reducing maintenance costs since the signals last so much longer than the old incandescents. It has nothing at all to do with saving electricity. It has everything to do with installing lamps so that the fixture does not need as much relamping as before. Of course, safety by reducing burnt lamps is also a big reason :)

On a lighter note, the very newest LED traffic lamps use diffusers so they look more like traditional lamps and not like 100 lamps. Here in Washington DC the green, amber, and red lamps are all being replaced and they are brighter and more attractive than the old lamps were. THey are much better than the green traffic lamps that Fairfax County is experimenting with.

Kris

Re:efficacy versus efficiency

[Jason1729]

but most do not use any more or any less energy than the equivalent incandescent or incandescent halogen at the same wattage.

That's like saying "what weights more, a pound of feathers or a pound of nails?". Wattage is a measuere of the energy you are using per unit time.

LEDs give off more light for the same power than incandescant bulbs; super-bright LED takes about 15mA at 1.7 volts. That's 25 miliwatts of power. For the same power a 100 watt lightbulb takes, you can power 4,000 super-bright LEDs.

The difference is even more extreme with flashlight bulbs. To get more brightness, the bulbs are run at about 25% higher than the rated voltage. This does make it a lot brighter, but at a bigger penalty for power draw, and cuts the life expectancy down from 1000 to 10 hours.

Jason
ProfQuotes

On the road

[__aafkqj3628]

Whoever does the traffic lights over here (I think it's the LTSA, but whoever it is doesn't really matter) is slowly changing traffic lights (busted ones and new ones) over to using LEDs instead of the traditional light-bulb.
The change is quite noticeable (when you see 500 LEDs peering back instead of a large bulb), but the LEDs seem to provide greater brightness in addition to a longer-life and better energy efficency (which is always good during our annual energy-crisis).

Re:On the road

[phelddagrif]

I find that the LED traffic lights are far easier to see in both the daylight and the night. They don't seem to be effected by sunglare nearly as harshly as the coloured glass sodium bulbs do. Which is nice because it can be a bitch to try and figure out what colour the light is sometimes. (It's not super hard,just much harder than it should be). Whereas the LED's are always readable. At least that's my experience with them.

Re:On the road

[bill_mcgonigle]

500 LEDs peering back instead of a large bulb

And the best benefit - when an LED fails you have 499 LED's instead of traffic accidents. :)

A long way to go...

[Eivind]

We hear that leds will replace ligthbulbs every 2 years or so, and yet, they are still not even in the ballpark.

A white led today has about twice the efficiency of a normal ligthbulb. That sounds great -- until you consider:

• The brigthest white led existing (in a lab environment, not on the shelves) is a 5 watt led, equivalent to a 10W ligthbulb, yay !
• Twice the efficiency ain't that good, this still means only about 10% of the energy-input gets turned to ligth, even halogen can do better than that and fluorescent has it beat into the ground with like 20-30%.
• The prices are out of this world, no, each LED ain't that expensive, but it also has a tiny ligth-output, try calculating the price for reasonably ligthing a single room.
• The color-spectra suck. Seriously, led is inherently monochromatic. Yes they can remedy this with various phosphors and the like, but those reduce efficiency (which was supposed to be the advantage of leds, remember?) and even with those it's hard getting a natural full ligth-spectrum.

In the meantime pluorescents are developing at a breakneck pace. Today you can buy pluorescents compact-bulbs that fit in a normal bulb-socket, are 5 times as efficient as a standard bulb, cost around 2$ a piece, are available in wattages up to 25 W (equivalent to 125W standardbulb), and last for around 10000 hours.

This is a no-brainer people. Replace a single 100W ligthbulb with a 20W energy-saver and the math looks like this over the 10000hour lifetime:

• Cost of bulb: 2$ instead of 5*0.20$, extra cost 1$
• Energy comsumed: 10000*0.02=200Kwh instead of 1000Kwh for the normal bulbs.

You pay 1$ extra for the bulb, and you save 800Kwh over the lifetime of the bulb. With an energy-price of 13 cent (most pay more!) you will save over 100 dollars over the lifetime of that single bulb.

Re:A long way to go...

[theedge318]

While you are correct that fluorescent bulbs are much more efficient, they serve a considerably different purpose. Fluorescent bulbs provide great omni-directional lighting. Unfortunately they produce some unwanted spectrums, namely don't store wine under anything but an incandescent bulb. Anyways LED provide a very tight cone of light. This means that they are perfectly suited for flashlights, traffic lights, and headlights, where we are looking for a cone of light that only represents 1/100th of the sphere. A fluorescent bulb may be 3 time more efficient, but it does so in directions that need to be reflected into the correct direction, a process that is only 10-20% efficient.

What does this mean ... you won't be replacing your household lamps with LEDs anytime soon (if ever) ... but flashlights, traffic lights, headlights, and other similar lights will all begin to make use of LED technology.

Re:A long way to go...

[mandolin]

One implication of the greater efficiency of the compact fluorescent light would be the lower heat output for a given brightness. So you need to run the air conditioner less often -> even less power used. Double the pleasure, etc.