Slashdot Mirror

The best modern available white LEDs (as of late 2007) produce about 60-90, maybe 98 lumens of light per watt of electricity delivered to the LEDs when the LEDs are supplied "typical" current or that at which their characteristics are specified. Many others that are in recent LED products achieve merely 20-45 lumens/watt. Most such white LEDs are and will be slightly more efficient when moderately underpowered and will usuallty be less efficient when overpowered.

OK, can someone tell me where my calculation is wrong:

The designer's diagram shows 50lbs of weight falling 58 inches. Google tells me in metric that's about 23kg falling 1.5m; under the force of gravity (9.8N/kg), that gives a total potential energy of 23*1.5*9.8 Joules—call it 350J to be generous.

Now, the claim is that this thing outputs 600-800 lumens of light. Let's assume that LEDs can put out 200 lumens per watt of electricity delivered—this is apparently quite generous. That means the LEDs will need at least 3 watts of electricity to give out that amount of light.

As everyone here knows, 3 watts is 3 joules/second—meaning our total of 350J will last slightly less than two minutes; this is substantially less than the claimed four hours!

Either my number-crunching is wrong (in which case I'd be delighted to be enlightened—excuse the puns), or this device ain't ever going to do what it claims...

8. CAUTION: contact with output will be painful, though probably not
  particularly dangerous due to low (a few mA) current availability.
 
  HOWEVER, if you add a high voltage capacitor to store the charge,
  don't even think about going near the HV!

LEDs, unfortunately, are way too dim right now for general-purpose lighting. They make great spotlights, but are lousy in terms in Lumens, and not that great in terms of Lumens/watt (before anyone argues with me, PLEASE compare lumens between LEDs and incandescents or CFLs).

Ummmm, LEDs? Referenced from http://members.misty.com/don/lede.html I find that 91.7 lumens per watt is 27.7% efficient. So 100% efficient would be 331 lumens per watt. From http://en.wikipedia.org/wiki/LED I see LEDs can produce up to 240 lm/W, and white LEDs have been demonstrated at up to 131 lm/W. Although, wikipedia also seems to think the theoretical maximum is 683 lm/W, so I guess these don't quite reach that. Still, I think red LEDs might.

Compact fluorescents, 50-70 lumens per watt off the shelf.

White LEDs, 30-45 lumens per watt off the shelf, 131 in the lab. And way more expensive.

http://www.netl.doe.gov/ssl/faqs.htm
http://www.cree.com/press/press_detail.asp?i=11508 34953712
http://members.misty.com/don/lede.html

Right now the reason to use LEDs is if the environment is harsh (vibrations, impacts, etc.) or if you really, really don't want to change the light often (traffic lights, or that %^#@!! bulb over my stairs). LEDs also scale down better than anything else.

>many companies (Lowes, Fred Meyer)

Recently, Fred Meyer was *still* selling Lights of America bulbs. Research what you're getting before you install it. I hope Lights of America has improved since the last time I bought any, at which time I saw one premature failure after another sometimes accompanied by alarming smoke output. More Lights of America comments.

The LEDs also produced more lumens per watt power consumption as well as used the lest amount of energy to turn on, whereas the traditional florescents had a 7x power spike for turn on, and the traditionals had a 1.5x spike, even the CFL's had a power spike. Everything says to use LED lights now.


Unfortunately we live in a market economy. The cost is a real factor. My average lamp is 900 Lumens. My 1 watt flashlight is only 32 lumens.

If I live another 30 years in my present home, what is the cost to outfit a 6 bedroom 3 bedroom home with LED lamps and will I have any savings over CF bulbs I now have installed?

LED lamps are about 20 cents / Lumen.
Refrence PDF alert. http://www.aceee.org/pubs/a042_l11.pdf

At 5 lamps in the kitchen overhead, 2 under the microwave, 5 in the dining room, 4 in the living room, 15 in bathrooms, 12 in bedrooms, 6 in porch and drive, 4 in the laundry, 2 in the hallway, and 5 in the rec room. Average size 60 watt equivelant. Total numbers of lamps is 60 for a total of 54,000 lumens needed.

To make matters of finding a proper replacement, many LED's are not rated in Lumens but intensity. I don't need a spot of light on the celing above the light. I want the room lit up. Remember there are aproximately 1,000 Mcd to a Lumen. Using that compare this bulb to a typical 14 watt CF lamp.

http://item.express.ebay.com/Home-Garden_Lighting- Ceiling-Fans__16000-MCD-P60-48-White-LED-110-V-Edi son-Type-Light-Bulb_W0QQitemZ220015435889QQihZ012Q QddnZHomeQ20Q26Q20GardenQQadnZLightingQ20Q26Q20Cei lingQ20FansQQcmdZExpressItem

I don't think a 16 lumen lamp is a direct replacement for a 14 watt CF lamp of nearly 900 lumens.

The LEDs also produced more lumens per watt power consumption

http://members.misty.com/don/lede.html
"The better usual modern white LEDs (as of September 2006) produce about 29-45 lumens of light per watt of electricity

http://hes.lbl.gov/hes/makingithappen/no_regrets/l ighting.html

"while the fluorescent produces over 50 lumens per watt"

The high effeciency LED's just are not on the market yet for most white LED's.

I'll stick with CF's as the additional cost of LED's don't yet produce a measurable savings. I have been watching the lumens/watt and cost race for some time. It's getting close, but the average modern white LED is still not as effecient as a typical CF lamp.

A laboratory prototype of a white LED achieving 150 lumens/watt has been announced on 12/20/2006.

Wake me when these are on the shelf at a competitive price.

You need to read your own references before you call bullshit on somebody.

Your articles say that they're more efficient that incandescent (duh), and Compact Flourescent. Those are at the low end of the efficiency scale.

White LEDs aren't even close to 100% efficient, because a large portion of the light they emit isn't in the visible spectrum. They don't work strictly like normal LEDs.

Efficiency wise, white LEDs fall between CF and traditional flourescent in producing visible light. I'd provide a reference, but there's no definitive guide, so instead I'll show you how to do the research and the math yourself. First read about how to determine how much light an LED actually produces, and why you can't compare lumens to candela directly. Then take a look at some incandescent and flourescent lamps, and you'll see that incandescent produces between 15 and 20 lumens per watt, CF produces between 40 and 75 lumens per watt, traditional flourescent goes up to about 100 lumens per watt, and high pressure sodium are around 140 lumens per watt.

The best white LEDs currently available produce 37 lumens per watt and there may be 60 lumens per watt LEDs available soon.

It pisses me off that blatent mis-information like what you posted gets modded up, while the truth doesn't, just because geeks have an unnatural love for LEDs.

The CF bulb is 32 times the cost of the incandescent.

Several dimmer switched on the site are under $10. A dimmer switch will dim several lights at once.

For the cost of 4 bulbs and a switch I can have nearly, if not more, energy savings and better lighting as a single CF bulb.

As for traffic lights, those are a special case, not white, and must be heavy-duty. But, that's beside the point:

LED lights for sale today are still less efficient than the average compact fluorescent, and nowhere near as efficient as fluorescent tubes, but these guys claim to have made a breakthrough. Perhaps LEDs that replace fluorescents could come soon after all.

Something interesting and useful to know is that the other reply you received to your post is totally incorrect.

First, LEDs are current driven, not voltage driven. The voltage difference between + and - determines the amount of current the device will consume, but if you can regulate the current you can run the device at 100V no sweat. You will of course need to dissipate any additional heat (usually in the device you're using to do the current limiting, sometimes a resistor, sometimes a more exotic circuit) created, but the very important thing to understand about LEDs is that their current absolutely determines their light output after you surpass a certain threshold voltage.

The relationship between the +/- voltage difference and the amount of current consumed is not the same for every kind of LED. LEDs require different chemistry in order to produce different colors, and this makes them have differing performance characteristics.

And another thing to consider is how the LEDs are packaged. Some 8mm packages have 4 chips inside and their rated light output is measured at a regulated input current of 80mA and not 20mA as for most single-chip devices. Also, some blue devices consume 30mA while reds only consume 20mA. Again, this depends on the chemistry. Now, also, taking packaging into consideration, a Luxeon device from Lumileds and a BL-3000 from Lamina Ceramics have totally different performance characteristics because of their chemistry, construction, packaging, and so forth.

You have two choices: Limit the voltage so that the device does not consume as much current, or limit your current and ensure that the voltage simply exceeds the maximum. Ultimately you need to regulate the current because the amount of current consumed (taking into consideration the device's ultimate efficiency) is directly proportional to the amount of heat generated in the chip itself.

You see, LEDs don't generate heat in their light path (radiant infrared travelling in parallel with the visible light, like the "heat" of the sun or a candle), but the chip itself does get rather hot, and if that heat isn't dissipated the LED chip will become physically damaged. Some of the materials used have melting points below 120 degrees, a temperature easily achieved by an LED not properly heatsinked.

So here's some tips: When you make LED boards (whether addressable matrices or simple blinky lights) you want to use a metal-core PCB or leave a portion of the LED's leads exposed in order to help dissipate the heat generated at the chip core and ensure longer chip life. LEDs don't just "burn out" one day, they will get dimmer slowly over time, and you can maximize that length of time by running them at less than their rated current, by cooling them actively or passively, and by using PWM to modulate their output.

Don Klipstein maintains a good set of information about LEDs: http://members.misty.com/don/ledx.html

Cree are claiming a white (phosphor-based) LED with 50% wallplug efficiency, according to Don Klipstein's Lighting Site. The link from his site is dead, though. Cree are also claiming that lab versions of a current LED achieve 70 lumens/watt, and a total of 85 lumens at 350 mA. You'd still need about 25 of these to get the light output of a 100W incandescent, though. Probably cheaper to drop 300 5mm LEDs into a dedicated fixture - Chi Wing's eBay store will sell you 300 16,000 mcd (maybe...) white LEDs for a little over $100, shipped. However, I can't really see spending $100 for a 100W bulb, ya know?

OTGH, though, I can see a distinctly untapped market for specialty, artistic LED fixtures that simply can't be realized with incandescents or fluorescents.

"When you shine a light on quantum dots or apply electricity to them, they react by producing their own light, normally a bright, vibrant color. But when Bowers shined a laser on his batch of dots, something unexpected happened. 'I was surprised when a white glow covered the table,' Bowers said. 'The quantum dots were supposed to emit blue light, but instead they were giving off a beautiful white glow.'""

And what if you replaced the phosphorus coating in a fluorescent bulb with quantum dots?

--

LED Efficiency

Bulb Efficiency (lumens per watt)

• Incandescent: 14-17.5 [1]
• White LED: 29-37.5 [1]
• Fluorescent: 50-100 [2]

[1] Why LEDs can be 10 times as efficient as incandescents in some applications but not in general home lighting!
[2] Are fluorescent bulbs really more efficient than normal light bulbs?

I'm a bit surprised at those fluorescent numbers... I don't have the box to one of my fluorescent bulbs handy to double check that, but I do know that while not as hot as incandescents, they become very hot to the touch when in use. I've never touched a lamp sized LED bulb however.

One disadvantage of fluorescents is that they contain mercury. Newer fluorescents may have found a way around this however; I'm not sure.

Not surprisingly, many of the websites I saw talked about future improvements in LED tech with goals around 100 lumens per watt.

LED technology gets me excited because it's so efficient.

LEDs make super-efficient colored lights - i.e., indicators on electronic gear, traffic signals, automotive brake and turn signals, etc. That's partly because the colored LEDs put out many lumens per watt, but it's also largely because no colored filter (which wastes 60-80% of the light produced) is needed with colored LEDs.

But even the best white LEDs are only slightly more efficient than typical 100-year-old-tech incandescent bulbs, and (so far, at least) far less efficient than older tech like flourescents and sodium lamps. White LEDs have become popular in flashlights lately because they have other characteristics that make them very good at that specialized task, not because they're terribly efficient.

You don't know what you are talking about. I can provide more evidence, but that was what I could find right off the top of my head.

Read Why a 1 mW Helium-Neon Laser Still Appears Bright a Mile Away and the surrounding text to get an idea of why this is not FUD. A powerful laser projecting a 4-foot spot into the cockpit would easily hit a pilot, and easily blind them.

(The article mentions a number of problems, including the fact that you might be significantly reducing the lifetime of your tubes by dimming them. YMMV.)

What I have in my living room are some long-live fluorescents to provide the bulk of the light, and some incandescents to change the colour and make the illumination more interesting. You might be able to do something similar without having to hook the tubes themselves up to the dimmer.

Actually, your assertion that lasers are the least efficient light sources is out of date. It's true that the old style gas lasers weren't particularly efficient, but modern laser diodes are the most efficient light sources yet invented, as discussed in
Sam's laser-diode FAQ"

For example, the 5mw green laser pointer that I bought a few months ago seems incredibly bright, and its two AAA batteries seem to be lasting forever.

Sorry, accidentally posted AC.

Not microwatts, milliwatts. AFAIK, CD players use lasers in the 1-5mw range. They just happen to put out their power much more efficiently than a 60W light bulb (i.e. brighter than the equivalent area of the sun)

This has some useful information. So does this.

Yes, easily. LED light output is essentially linear; directly proportional to LED current. Incandescents are more complex to control (intensity as fourth power of applied voltage, spectrum shifting toward the blue as fillament temperature increases (google "black body radiator) fluorescents
are very difficult to control over a wide range of brightness.

try Dons light, lamp and strobe site>

I guess some posts just never go out of style;

Lumens/Watt Light Source
14.5 60W Incandescent A19 Bulb, softwhite (standard bulb)
17.5 100W Incandescent A19 Bulb, softwhite
17.5 Tungsten Halogen Single-End SUPER-Q Frosted Finish D.C. Bay 100Watt
60 150W single ended compact metal halide lamp
64 250W mogul based metal halide lamp, clear
84 32W, 48" MOL, T8 OCTRON fluorescent lamp,
100 Sylvania 18 watt low pressure sodium
115 1000W dual arc-tube high pressure sodium lamp, clear
150 90W low pressure sodium lamp, clear

(Data mostly from Sylvania's web site)

Normal LEDs have been improving rapidily.
The best commercially availble are 30 lumens per watt.
(You can get those in a lightwave 4000 flashlight)

Cree has developed laboratory prototypes of white LEDs that have achieved 65 lumens per watt in industry standard packages and 74 lumens per watt in special packages. Worse than fluorescent, but not by much.

Don Klipstein's Lighting Info Site is one of the better information sources IMO.

-- this is not a .sig

Given: 4 watts of total consumption to achieve a travel-size TV projection.

Assume: 2 watts of that are dedicated to the generation of light for that projection.

Possibilities:

1) Use a white light source, which means (for that size and power level) white LEDs. Those are commercially available at 25 lumens/watt. This gives us 50 lumens, which will not make for a wall-sized image viewable except perhaps in pitch-black darkness. However, for a smaller image... say, 16"x12"? ... this is equivalent in brightness to an 1800-lumen projector making an 8' x 6' image. That's fairly bright...

By 2005, 60 lumens/watt white LEDs will be out of the lab and into the market. This allows for our hypothetical projector to realize 120 lumens, or roughly 1/10 the output power of an 1100 lumen projector. You could make a 32" x 24" (40" diagonal) image at the same brightness as that 1100 lumen projector makes an 8' x 6' image.

2) use multiple colored light sources, again LEDs. Most of the 'brightness' comes from the green, less from the red, least from the blue. You can assume 50 lumens / watt off the shelf right now, which probably means a 32" - 40" diagonal image from those 2 watts, at the same brightness as an 1100 lumen projector making an 8' x 6' image.

Conclusion: *current* technology allows for TV-sized images to be produced, at brightnesses similar to those of larger images from brighter projectors, from only 2 watts of input power to the optical source.

Sources: Don's LED Page.

Disclaimer: comment author has been an A/V professional since 1987, holds masters in EE.

>An LED is less efficient than an incandescent bulb.

Which LED? Which incandescent bulb?

If you're talking about, say, old SiC blue LED's compared to a 100W incandescent, you're right.

If you're talking about a modern white LED (phosphor over GaN or InGaN, usually) compared to that same 100W incandescent, you're dead wrong.

If you're talking about colored incandescents vs. monochromatic GaN /InGaN LED's, you're so far wrong that three lefts won't make you right. In fact, current red/orange LED's are about as efficient as compact fluourescents. That's mighty mighty, as the man said.

May I suggest Don Klipstein's Lighting Info Site! as a gentle introduction to the current state of affairs in LED lighting?

I really don't think you know the field well enough to make sweeping statements like that.

As always, it depends on the use.

I haven't seen anything about manufacturing costs, so maybe I'm not answering your question, but in use:

In traffic lights, a burned out bulb is a hazard, and expensive to change.

Brake lights and taillights are dangerous to lose, and they get shaken around. That's why in many cars if your brake or taillights go out, your dash lights go out too as a reminder.

Flashlights are typically low temperature bulbs where incandescents are more inefficient, especially after the battery voltage starts to drop off. Besides, they get dropped, so LEDs are a win there too.

Fluorescents are the most effecient, but for household lighting I don't like their color or sixty Hertz visible hum. (Any specific recommendations for a compact fluorescent that has a good color & a nice ballast that doesn't flicker sixty times a second?)

The LED geeks know LEDs aren't always better as far as power consumption goes.
http://www.pioneernet.net/optoeng/LED_FAQ.html#Q7
http://misty.com/people/don/lede.html

I saw a nice use of LEDs in a remote campsite. There were solar collectors on the roof of the bathroom, and little banks of a few LEDs that lit the bathrooms at night.

An LED seems smaller, but the incandescent in a mini-maglite puts out much more light than a white LED of the same size.

I did a little digging triggered by a reply about the efficiency of various lights in lumens-per-watt. Not believing what I read, I dug a little on the web and found a decent exploration of the problem at Don Klipstein's website titled Why LEDs can be 10 times as efficient as incandescents in some applications but not in general home lighting! I got there after reading an article on custom boat cabin lighting with LEDs at Noemi Ybarra's site which includes an outline of the physics behind the units (i.e. 1 lumen is (4pi steradiansx1candella) only if the light source is uniformly spherical, which LED's are not, so the big "mcd" ratings don't correlate well to really big "lumen" ratings.)

For buying:
Hosfelt

For info
Don's light site
LED museum

according to Sam's laser FAQ, DVD lasers emit at 635 nm, whereas CD lasers emit at 780 nm. I'm still trying to find a sources explaining why a lot of DVD players don't support CD-R's

Get involved

I own the PrincetonTec LED headlamp, I've read the LED article in Technology Review recently, and I've followed many links on the web about white LED's, and the following seem to be the relevant facts for headlamp and homelamp applications:

The current efficiency for a white LED is limited to about 20 lumens/watt (see the Technology Review article or www.misty.com/~don/led.html#w.

The reason that they do not put out much heat is that they do not put out much light either (though enough for some tasks).

Compact Fluorescents currently run about 50 lumens/watt (a 15 W, 750 Lumen unit costs $5-10), so it is clear that if you have access to AC power, you can forget LED's unless a drastic change in efficiency happens.

Halogen flashlight bulbs (state of the art Xenon) run about 10-20 lumens/watt (more for the higher power ~4W bulbs). Sorry, I lost the reference for this one.

The reason LED flashlights have become popular is that, for low power applications, halogen lights don't scale well and normal incandescent bulbs are not very efficient (~5 lumens/watt).

That being said, I must say I like my PrincetonTec lamp - it does go about 40 hours and is bright enough to comfortably read and walk on reasonable trails. I (along with others) reviewed this lamp on outdoorreview.com/reviews/Headlamps/product_2333.a sp.

you will see that as well. It's not like there will only be one display technology in "the future". blue LEDs are a short term problem. new & expensive. see blueled.com and Don Klipstein's LED page

Get it right here:

Fluorescent Lamps, etc... Faq

Lots of other interesting info there too. Like Arc Lamps, etc... );-)