Quick Quiz: What is the Most Efficient Artificial Light Source?
by Team Treehugger, Worldwide on 12.19.06
The efficiency of a light source is measured in lumens per watt- simplified, the luminous power measured in lumens divided by the electrical power measured in watts. The more lumens per watt, the better the light source in terms of energy efficiency. A lot has changed in the last few years; what do you think is the most efficient light source? Answers after the fold, but no peeking! We can tell.
After spending hours making my own list, of course there was this neat table from Wikipedia which agrees with our other sources. I was surprised by the results.
1) Low pressure sodium lamps were far and away the most efficient, at 200 lumens/watt, but they give out a single orangy -yellow frequency of light and have been used mainly as roadway lighting. While I always found them easy on the eyes when driving, evidently the police didn't like them because it is impossible to tell the colour of a car, everything is grey or orange. They are being replaced by less efficient high pressure sodiums.
2) Next best are the high intensity discharge lamps like the metal halides (seen in big box stores and gymnasiums) and high pressure sodium (exterior and roadway lighting). at 150 they are every efficient but always big and bright, not suitable for home use.
3) Conventional fluorescent tubes are currently in third place, but that really depends on the colour temperature (cool white is more efficient than warm white)
4) Compact Fluorescents are slightly less efficient than long tubes at this time, but obviously far more efficient than the incandescents they replace.
Tied for 3 or 4) LED's, at 26 to 70, are not yet more efficient than flourescents, but are catching up; in the lab there are prototypes up to 131. They are also coming out in MR16 sizes to replace existing halogen fixtures, although they are still expensive.
5) Quartz Halogen fixtures are better than conventional incandescent at 24 but are evil little things. They are in fact, a very small incandescent that would melt if not made from quartz. 10 years ago they were all the rage, and I have a ceiling with 18 of them. They are extremely hot, they require transformers that burn out, and you can't just change the bulbs to CFL,s but have to wait until the LED replacements are bright, affordable and a decent colour temperature, which they are not yet. There have been many recalls of cheap quartz halogen lamps causing fires. They should be put out to pasture as quickly as incandescents. IKEA has lots of lovely quartz halogen designs that look so modern, but keep away.
6) Way down there at the bottom:
The incandescent lightbulb, all of which belong a museum with this one.
Be sure to read How to Green your Lighting again!
Interesting post, good to dispell some of the LED myths.
It's 'fluorescent', by the way.
LA: You are right about the spelling! I can't correct the survey but have the copy. Thanks.
You missed the word 'electric' out of the question, by the way.
I second what Daithi said, otherwise it would be sunlight.
Ah, unfortunately not so simple. First of all, LEDs emit light in one direction, compared to incandescents or fluorescents which emit in all directions. This means, in many applications like a desk lamp, an LED with an efficiency of 50 l/w delivers more light to the desk than a fluorescent with 75 l/w. That's why many lighting energy standards are now being written on "Lux/watt"- that is the electrical efficiency of light delivered to the user.
Secondly, lumens are a measure of optical power reference to a lamp emiting green light (where the eye is more sensitive). This makes it hard to compare a single color light- like a sodium lamp, to a white light. Because the eye varies in sensitivity to different colors, a lamp which better matches the eye's sensitivity- even though the "wall plug efficiency" is lower, is actually more efficient, because you can use a lower wattage bulb to achieve the same human-percieved brightness. And then there are issues of dimming, efficiency of a high voltage power supply instead of a low voltage, etc.
Most studies indicate white LEDs are more efficient than the alternatives, in actual field applications, once they pass 50 l/w.
The low pressure sodium lamps have another advantage, which is that they emit their light in a single frequency band. This makes it easy for astronomers to filter out. They are very common in Hilo, HI, for that reason.
During the daytime, natural sunlight is obviously very efficient (from an electrical power consumption perspective) - whether through solar tubes or through windows.
What about photo-luminesence? Some glow-in-the-dark substances can work for some interior lighting needs.
Chemlights? Crack'em and they light up for a while. Efficient, doubtful. Ubitquitous, inexpensive, and portable though.
I haven't heard of anyone filling a fish tank with bio-luminescent creatures to light their home, but that could make for some interesting lighting options.
what is best greenhouse light? Radiant? might also supply heat needed in winter and would shine only on plants.
Halogens may be evil from a green standpoint, but they deliver the most beautiful artificial light available. Nothing compares for accent lighting of artwork or architectural features.
Hopefully, a suitable replacement will be developed with those characteristics in mind.
Odd, I intuitively went for the right answer, but logic indicated LED to be my choice.
Anyway, it is apparent that this sort of quiz can only be a useful guide when one considers the comments of others. The actual use of the lighting can make the results totally different. For instance, I use candles as my background lighting if I am watching video or sometimes whenworking on my computer. This gives me a pleasant ambient light of exactly the quality I desire AND heats the room. According to the chart, this is a bad choice, but considering my actual use, is this still so?
Raleigh, NC will become an 'LED City'. Cree Inc. will install its LED lighting into public fixtures.
Available on EBay for $75, a 560 lumen bulb made from 7 LEDs screws into a normal fixture and only consumes 7 watts. These bulbs are 8 times more efficient than the 60 watt halogens ($10 each) that populate the 28 recessed lights in my home. Since the LED lifetime is at least 10 times longer than the halogens, there is a cost justification for the bulb replacement alone, not even counting the illumination energy savings. LEDs work with the existing dimmers as well.
To avoid overheating, the recessed light fixtures are designed to leak the house air into the attic and cannot be covered with insulation. If the halogens bulbs were replaced with LEDs then the fixture holes could be plugged and covered with insulation saving on heat and air-conditioning costs.
We should encourage the environmental and patriotic use of the rapidly emerging LED technology.