Integrated Reflector Could Lead to Ubiquitous LEDs

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Integrated Reflector Could Lead to Ubiquitous LEDs

Posted by timothy on Sunday July 25, 2004 @02:04AM from the in-your-eye dept.

Andreas writes "Professor Schubert says he has found a way to raise the efficiency of LEDs to 99%. From an article on Advanced Technology: "Until now, all lighting systems, especially incandescent bulbs, generated more heat than light. But our 99-percent efficient reflectors for LEDs makes them the first candidate for light-bulb replacement that generates more light than heat," said Schubert."

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Not so fast, Sparky! by rco3 · 2004-07-25 02:14 · Score: 4, Insightful

"Professor Schubert says he has found a way to raise the efficiency of LEDs to 99%.
No, that's not what he says. The reflector is 99% efficient, not the LED. This reflector just means that some of the light emitted by the LED, which otherwise might be absorbed by the LED substrate or other structure and converted to waste heat, is now being reflected back out as usable light.
This new technology does nothing to improve the quantum efficiency of the LED itself. It's an important and useful technology, sure, but it is NOT a 99% efficient LED.

--

Ce n'est pas un vrai mouvement de robot!
1. Re:Not so fast, Sparky! by Pinkoir · 2004-07-25 02:42 · Score: 2, Informative
  
  As the man says, a 99% reflector is not a 99% LED but this technology would certainly seem to be a useful advance.
  
  Some current LEDs already use thin flim techniques and reflectors to collect the rear emitted light and throw it out the front but this is the first I have heard of combining the reflector with the wiring. This might also have the potential of moving heat out of the junction more efficiently would would be a real help in a lot of applications.
  
  Still I'm curious about how much this will add to the cost of a white LED. There is no point making a bright LED if the total system cost is still ten to twenty times that of an incandescent source. I'm an illumination engineer in the automotive field and when we look at replacing a bulb with LEDs we have to add in not only the cost of the LEDs themselves but also the board, the heatsink, the drive module and associated cicuitry. So while it is true that more light and less heat would be better the real roadblock in my application is cost and we won't see the widespread replacement of filament sources with LEDs until that issue is resolved.
  
  -Pinkoir
Costs have to be considered in toto by Engineer-Poet · 2004-07-25 03:04 · Score: 4, Insightful

Quoth the poster:
There is no point making a bright LED if the total system cost is still ten to twenty times that of an incandescent source.
As a counterexample, consider the compact-fluorescent bulb. Most cost around ten times as much as an incandescent of equivalent brightness, but the savings in replacement costs and power will pay back the difference in as little as a few months.
LED technology has the advantage of longer life than fluorescent. With the increase in efficiency from reflectors, they could cut power costs below fluorescent and become the TCO winners.

--

Sustainability and energy independence essay
1. Re:Costs have to be considered in toto by Elledan · 2004-07-25 03:27 · Score: 4, Informative
  
  "LED technology has the advantage of longer life than fluorescent. With the increase in efficiency from reflectors, they could cut power costs below fluorescent and become the TCO winners."
  
  Also something to keep in mind is that LEDs are far more robust than fluorescent and incandescent lights. Incandescent lights can't take shocks very well, and the huge temperature delta between an on/off state reduces its lifespan significantly. Fluorescent lights are also relative fragile (ever tried replacing fifty or so of those tubes without shattering at least one of them?), and the ballast used to generate the required high voltage (most types of ballast) create quite a lot of EMI, which is bad for sensitive equipment and cables like Cat-5 etc.
  
  LEDs generate very little heat, require only a very small current (tens of mA!) at equally low voltages, produce no EMI, are unaffected by all but the most severe shocks and last virtually forever (100,000 hours for red, green, etc. with ease).
  
  If LEDs are made brighter, even if this makes them more expensive than other technologies, there are always some (less friendly) places where they would work very well and would be cheaper in the long term.
  
  --
  Site & blog: http://www.mayaposch.com
2. Re:Costs have to be considered in toto by Anonymous Coward · 2004-07-25 04:47 · Score: 0
  
  > If LEDs are made brighter, even if this makes them more expensive than other technologies, there are always some (less friendly) places where they would work very well and would be cheaper in the long term.
  
  It's true! Some time ago (1-3 years?) our city started using LED clusters for almost any traffic light, new or replacement. Same with all the indicator lights on the buses around here. LED xmas lights sold like hotcakes last year. Unfortunaly the xmas lights are built with two circuits, blinking alternately at 60hz for each circuit. Personally I can't stand them, the blinking bugs the shit out of me. Whenever I move my eyes I see the blinkiness. Anyhow.
3. Re:Costs have to be considered in toto by Vengeful+weenie · 2004-07-25 18:08 · Score: 2
  
  I'd probably add the fact that fluorescent bulbs are environmentally problematic, and can be dangerous to health. While manufacturing LEDs undoubtedly create waste by-products, I would doubt that they would be much worse than when manufacturing fluorescent bulbs.
4. Re:Costs have to be considered in toto by cmowire · 2004-07-26 17:58 · Score: 1
  
  Ahh, but a compact flourescent is still more efficent than an LED.
  
  --
  Gentoo Sucks
5. Re:Costs have to be considered in toto by JosKarith · 2004-07-26 23:33 · Score: 1
  
  "tried replacing fifty or so of those tubes without shattering at least one of them"
  Yes. Yesterday in fact.
  Course it helps that I'm tall enough to reach the fittings without a ladder...
  
  --
  'Don't worry' said the trees when they saw the axe coming, 'The handle is one of us.'
How are narrow-angle traffic-signals done? by nusratt · 2004-07-25 03:22 · Score: 1

Several years ago I researched this on the web, but never really reached a satisfactory resolution.

There's a type of traffic signal whose illumination is clearly visible only within a narrow angle. As you approach the intersection, you can see all three *lamps/lenses*, but you don't see which lamp (r/y/g) is currently *lit* until you enter within a certain angle of the lamp.

Can anyone *authoritatively* explain how this is done in *this* application?
1. Re:How are narrow-angle traffic-signals done? by zrail · 2004-07-25 03:50 · Score: 5, Informative
  
  These lights use a Fresnel Lens to direct the light from the bulb or LED cluster to only the lane for which it is intended.
  
  wikipedia link
2. Re:How are narrow-angle traffic-signals done? by Cuthalion · 2004-07-25 07:26 · Score: 1
  
  Of course, they'd work fine too with a regular lens, but that's more expensive and heavier.
  
  --
  Trees can't go dancing
  So do them a big favor
  Pretend dancing stinks!
3. Re:How are narrow-angle traffic-signals done? by nusratt · 2004-07-25 14:52 · Score: 1
  
  When I last researched this several years ago, I asked about Fresnel and never got a straight answer (even from the manufacturer).
  Your link, however, EXPLICITLY says, "yes, that's how it's done."
  Thanks!
110/230V AC by EnglishTim · 2004-07-25 03:34 · Score: 4, Interesting

Okay, so let's assume all our lightbulbs start being made from LEDs... At some point soon we're going to have to start changing our lighting circuits to 5V, or something like that. It's madness that each lightbulb will have to contain it's own little transformer - it'll make the bulbs vastly more expensive and wasteful.

There are a selection of appliances that work well with 110/230V AC - things that require a lot of power like kettles, hoovers, heaters, washing machines, hobs, tumble driers and the like. However, there's an increasing number of appliances in a modern household that would be much better served by a 12V DC supply.

How long do you think it'll be before we start changing over?
1. Re:110/230V AC by Smidge204 · 2004-07-25 04:25 · Score: 4, Informative
  
  Unfortunately DC power doesn't transmit over any kind of distance very well. AC is much more efficient for that. (Esp. at high voltages... 20,000V+)
  
  Also, all flourecent lights have transformers in them, so suddenly it's not too unreasonable for each light fixture to have its own little transformer in it!
  =Smidge=
2. Re:110/230V AC by alienw · 2004-07-25 04:35 · Score: 2, Informative
  
  Running 5V around the whole house would be much more inefficient than putting a transformer inside each bulb. It would also be expensive, and a fire hazard. Think about it: running 1kW of power through a 5V system would require 200 amps of current! That would require welding cable-sized wires.
3. Re:110/230V AC by bluGill · 2004-07-25 05:01 · Score: 3, Informative
  
  Electronics 101: when you connect 2 circuits in series each sees half the total voltage. Connect 24 LEDs in series to a 120 volt line and each sees 5 volts! By definition there is no need to transform the AC into DC - the D in LED stands for diode, which is what you use to turn AC into DC! In the real world you are likely to use 48 LEDs, in two different strings, so that you get light from both sides of the wave.
4. Re:110/230V AC by Sparr0 · 2004-07-25 05:27 · Score: 1
  
  I have had this thought as well. For quite a while I have considered a 12V wiring system, and at this point I have decided that my next house will have one. Nay sayers will tout the dangers of DC, as well as the inefficiency. But what they dont realize is that a well designed system doesnt have to pump a gazillion amps over every line. Any individual outlet doesnt need to provide more than a few amps, since 'normal' =12V applications dont pull much power (cell phone charger, LED light, etc). A well thought out load detecting circuit, as well as multiple runs to each circuit, would allow this to be handled with ease. And, as to inefficiency, the loss of DC over 20-40ft cables is noticable, but not enough to offset the increase in efficiency of using one large well designed (expensive) transformer instead of a hundred small cheap wasteful ones.
5. Re:110/230V AC by Anonymous Coward · 2004-07-25 05:55 · Score: 0
  
  Some naysayers will also require that you follow wiring code. But other than that good luck on your next house. Write up a webpage to be Slashdotted when it's all built. :)
6. Re:110/230V AC by SuperBanana · 2004-07-25 06:00 · Score: 3, Informative
  
  It's madness that each lightbulb will have to contain it's own little transformer - it'll make the bulbs vastly more expensive and wasteful.
  If you have 2v LEDs, you only need wire about 60 of them in series and you've taken care of the voltage problem. Well, except they'll blink at 60hz, quite strongly...and if one failed, they'd all go out. But in any case, it's hardly rocket science to make use of the higher voltage level, especially since LEDs will tolerate A/C. Incidentally, look at a screw-in fluorescent bulb some time- they've gotten the whole thing down to $10 or so, and that includes a transformer and electronics to raise the voltage. Transformers etc are very cheap.
  However, there's an increasing number of appliances in a modern household that would be much better served by a 12V DC supply. How long do you think it'll be before we start changing over?
  Never. The whole point behind A/C is that it is very easy to step up/down, and as a result, you can use a higher voltage for transmission and distribution. Higher voltages mean less current flow for the same amount of energy, which means reasonably sized wiring and such.
  Even in the short distances involved in a house, losses from wiring can be substantial at such a low voltages as 12v. 48v might be a better choice, but I can't see it ever taking off.
  
  --
  Please help metamoderate.
7. Re:110/230V AC by darkjedi521 · 2004-07-25 06:08 · Score: 1
  
  But welding cable sized wires are fun! I've run (theatrical) lighting systems off 0/4 cabling - an accidental short is pretty impressive, tripping the breaker for the building mains. I've learned the hard way not to trust my school's electricians when there is more than 120V/20A involved
8. Re:110/230V AC by falzer · 2004-07-25 06:18 · Score: 4, Informative
  
  > Unfortunately DC power doesn't transmit over any kind of distance very well.
  
  Looking at just the wire itself, transmission losses aren't worse for DC. There are a few HVDC transmission lines in operation now. Some are used for 50/60Hz conversion.
  
  The reason AC is used because it's easier/cheaper to efficiently step up (and down) the voltage to useful levels, as per your power transmission example.
9. Re:110/230V AC by Peepsalot · 2004-07-25 06:32 · Score: 3, Interesting
  
  It's madness that each lightbulb will have to contain it's own little transformer - it'll make the bulbs vastly more expensive and wasteful.
  Sorry, I don't think you'll see a change(at least not to a lower voltage) in your wall outlet's voltage any time soon. Maybe a transformer in every light bulb seems wasteful, but take into consideration that led's can last roughly 100,000 hrs as opposed to 1,000 for incandescant's.
  
  Still seems wasteful?
  Transformers don't have to be huge, especially if they are powering an efficient device that doesn't draw much power. Disposable cameras contain transformers in them that step the voltage from 1.5 to 300 volts, and they are pretty damn small. In fact you could fit a transformer into just the metal base of a normal incandescant bulb. Not to mention the transformer's solid state cousins: voltage regulators, swithcing power supplies, and probably some others I don't know about (IANAElectrician.)
  
  In fact, you could also scrap the idea of stepping down the voltage entirely. How about putting more led's in series. Think about it, led's emit a narrow spectrum of light, so to smoothen out the spectrum, you might want to add a bunch of led's from different parts of the spectrum. Just put 40 little 3v led's on a board and voila, you have a device that accepts 120 volts. Another reason to use a large number of leds: you might want to spread out the surface area where the light is coming from, a single point of light could seriously mess with your vision. Not to mention the fact that I doubt to see any single led in the near future that can output the equivalent of a 60 watt incandescant light bulb.
  
  But the thing the I wonder about is if and when the standard plug model will be changed to a model where the socket and the plug contain coils to transfer the power, like an isolation tranformer that is split into two parts.(Have you ever seen how a sonicare toothbrush charges itself?) The main benefit I see in this is safety; never have any exposed wires to fry yourself with. Actually, if all your wall sockets had coils in them, the plug of your device could determine the voltage that device receives, simply by the nuymber of coils in it. Again, IANAE, so I don't know, maybe it would take the advent of room-temperature superconductors to make this idea feasible and efficient.
10. Re:110/230V AC by Anonymous Coward · 2004-07-25 06:33 · Score: 0
  
  You don't trust your school's electricians, yet you speak of accidental shorts with lightning systems that you've run?
11. Re:110/230V AC by rco3 · 2004-07-25 07:09 · Score: 4, Interesting
  
  A few points to note, realizing that not many posters around here are EE's:
  
  1) LED's are not voltage mode devices. There IS a typical voltage drop associated with an LED, but it can vary appreciably between devices. One sets the operational point of an LED by controlling the current through it, and allowing the voltage to settle to whatever value it wants. Typically, one would want to see around 30 mA through a normal T1-3/4 LED. Depending on the chemistry of the LED, this could result in a voltage anywhere between 1.5V and 3 or 4V. This, as I said, will vary somewhat between different LED's of the identical type. If you try to set the voltage, you'll get wildly varying currents and a lot of dead LEDs.
  
  2) Stringing together LEDs in series to get something approaching 120V drop is a good idea, but you still have to limit the current. Leaving a few volts between the nominal operational voltage of your LED string and the nominal supply voltage is a good idea, because you can then use an active (or passive) current limitation scheme which operates within that voltage gap. The simplest way is with a single resistor, sized such that R= (Vsupply-VLEDS)/ILEDS. This is subject to variation due to device mismatch, temp variation, etc, and dissipates some power in the resistor. Another way to do this, which allows for the LED to be operated from a much higher voltage than it's rated for, is to use a series capacitor. The determination of proper capacitor size is a bit more tricky, but you can successfully run a single LED from a 120V supply. The indicator in my waterbed heater has run this way for a couple of years now. Nice part is that the capacitor does NOT dissipate any power as heat. Enough of them might screw up your power factor enough to piss off the power company, though :-)
  
  Important messages to take home from this: you can't set LED operating point from the voltage across it, at least not safely and reliably; you can operate LEDs from 120VAC using a capacitor as the gain setting element, which is appreciably cheaper than using a transformer.
  
  --
  
  Ce n'est pas un vrai mouvement de robot!
12. Re:110/230V AC by pediddle · 2004-07-25 07:46 · Score: 1
  
  Can you say "epileptic seizure"?
13. Re:110/230V AC by Ogerman · 2004-07-25 09:16 · Score: 1
  
  Electronics 101: when you connect 2 circuits in series each sees half the total voltage.
  
  Electronics 102: when you connect 2 equal non-reactive loads in series, each drops half the total voltage.
  
  In the real world you are likely to use 48 LEDs, in two different strings, so that you get light from both sides of the wave.
  
  In real world, you use a full-wave rectifier so that all 48 LEDs light during both sides of the wave.
14. Re:110/230V AC by KingPrad · 2004-07-25 09:20 · Score: 1
  
  I am wondering why you would have to put a transformer in each bulb. Why not just put one in the light fixture itself? Another poster mentioned that all flourescent lightbulbs do have their own transformers, so perhaps there is a good reason the fixture couldn't have its own. Could someone comment on this?
  
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  Stop the Slashdot Effect! Don't read the articles!
15. Re:110/230V AC by Bloater · 2004-07-25 09:20 · Score: 1
  
  That's really interesting. Can you elaborate on how the series capacitor works because my school physics education is becoming hazy now?
  
  Is there any problem using that also on 230V A/C?
  
  What about reducing flicker?
16. Re:110/230V AC by Bloater · 2004-07-25 09:23 · Score: 1
  
  oooh, oooh, I get it!
  
  Because the LED is in series with the capacitor, the voltage drops, ensuring that there is a differential in the EMFs from the supply and the capacitor, and a current always flows.
  
  But the supply must be rectified and smoothed first, I suppose. Also solving the flicker.
  
  Do I get any soup?
17. Re:110/230V AC by Amorpheus_MMS · 2004-07-25 10:20 · Score: 1
  
  In the real world you are likely to use 48 LEDs, in two different strings, so that you get light from both sides of the wave.
  Me thinks using half of them with a rectifier would be more efficient - same amount of light with a bit more than half of the components. (Although the other may actually turn out cheaper, who knows...)
18. Re:110/230V AC by darkjedi521 · 2004-07-25 12:39 · Score: 1
  
  Standard flourescent fixtures have their ballasts as part of the fixture.
  The compact florescents designed to be used in incadesent fixtures have their ballast built into the lamp.
19. Re:110/230V AC by Anonymous Coward · 2004-07-25 13:57 · Score: 0
  
  just an idea. why not wire each room with its own lighting transformer. use the same 110 volt system but each room will have one or more transformers depending on their size.
20. Re:110/230V AC by Jack+Schitt · 2004-07-25 14:37 · Score: 1
  
  Why not create a device that plugs into the standard 110v ac incandescant outlet (the standar screw type). The device would have the transformer in it. The bottom half would have some other fixture type (circular 12v dc car outlet). Each led bulb would fit into the secondar fixture. This way if the leds fail (never seen it happen), you don't have to replace a perfectly good transformer.
  
  I would rather wire a 12v dc circut with special fixtures instead of putting a device in each fixture as transformers are incredibly inefficient.
  
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21. Re:110/230V AC by Jack+Schitt · 2004-07-25 14:48 · Score: 1
  
  >>However, there's an increasing number of
  >>appliances in a modern household that would be
  >>much better served by a 12V DC supply.
  
  While it would seem to be a good idea for the power companies to hook up a 12v dc circut to your home, you must remember why the power companies use such high voltages to begin with. It has to do with the resistance of the wires.
  
  The best way to transmit 100,000 watts of electricity is at 100,000v AC at 1 ampre versus 1v AC at 100,000 ampres. The more ampres you cram into a wire, regardless of the voltage, the higher the temperature of the wire (to those people who may get angry at the way I phrased this, you try and explain it a bit better).
  
  DC cannot be transformed the way AC can. DC voltage is changed by adding a load to the current (i.e. a resistor). While this will work with AC as well, generally, induction is used instead.
  
  If anybody thinks I am incorrect, please correct me here.
  
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  This message brought to you by Jack Schitt's Previously Shat Shit
22. Re:110/230V AC by Handpaper · 2004-07-25 15:05 · Score: 1
  
  Can you say "epileptic seizure"?
  Can you say 'persistence of vision'? AFAIK, epileptics do not have a problem with cinemas (24fps/Hz) so why should there be a problem with the 25/30/50/60Hz cycle this setup would give?
23. Re:110/230V AC by Anonymous Coward · 2004-07-25 15:09 · Score: 0
  
  Another reason for a full wave rectifier, you would very likely shorten an LED's life by applying reverse voltage. It will be interesting to see if yield, efficiency, flicker and heat dissapation would allow a cheap multiple LED on a chip solution for high voltage.
24. Re:110/230V AC by Anonymous Coward · 2004-07-25 15:24 · Score: 0
  
  Maybe I'm mistaken, but I had the impression he meant it was the school's electricians that caused the short.
25. Re:110/230V AC by Alsee · 2004-07-25 15:30 · Score: 1
  
  Even better you throw in a capacitor with the rectifier to smooth the power. Reduces the flicker when you move your eyes and improves LED longevity by lowering the peak power.
  
  -
  
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26. Re:110/230V AC by Anonymous Coward · 2004-07-25 15:32 · Score: 0
  
  I am an EE and this capacitor ballast has me puzzled. An ideal recitifier in series with an ideal capcitor will eventually charge the capcitor up to the peak AC voltage and stop conducting and the recifier at times required to withstand a reverse bias of the AC peak to peak voltage. Maybe there is another effect unmentioned, such as two LED's head to tail. I also suspect that their is also something to protect this circuit from transients.
27. Re:110/230V AC by Alsee · 2004-07-25 15:56 · Score: 1
  
  Rectifying/smoothing is optional. You could simply put a pair of oppositely oriented LED's in parallel then connect the pair in series to the capacitor, end of circuit. Only a very limited current can flow into/out of the very small capacitance, and each phase of the AC flows through one or the other LED. Note that it is a particulary small capacitor to limit total current flow each phase rather than a large one to pass AC current.
  ......+LED- AC___/.....\__)capacitor(___AC .... \...../ ......-LED+
  Interesting circuit, I never came across it before.
  
  -
  
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  - - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
28. Re:110/230V AC by Anonymous Coward · 2004-07-25 18:24 · Score: 0
  
  Oh, well maybe I read it wrong too. In that case, I'm sowwy.
29. Re:110/230V AC by pediddle · 2004-07-25 18:38 · Score: 1
  
  Movie projectors and TVs cycle at about 30 hertz, but the light output from them is relatively constant even though the image is changing. On the other hand, haven't you ever seen the flicker of a fluorescent bulb? How about your computer monitor? These kinds of flickers are both on the order of 60 hertz, yet you can see them.
  
  An LED would flicker a thousand times more noticeably because LEDs have a response-time on the order of 0.5 milliseconds. Additionally, an LED in a pure AC circuit couldn't help but flicker because it's a diode, so it would only light half the time when the current flows in one direction.
30. Re:110/230V AC by pauldy · 2004-07-25 20:57 · Score: 1
  
  Enough of them might screw up your power factor enough to piss off the power company, though
  
  This only works if you are working with inductive loads like motors and such not resistive loads like what you would find through a led.
31. Re:110/230V AC by hcdejong · 2004-07-25 21:12 · Score: 1
  
  While 12V is a popular choice for low-voltage inputs, it's by no means the only one. Your cell phone (or whatever gadgets you want to power) is just as likely to require a 6V or 9V input. How are you going to handle that?
32. Re:110/230V AC by Grab · 2004-07-25 21:29 · Score: 1
  
  If you use a full-wave rectifier (or just use two strings of LEDs), both the positive and negative sides of the cycle will cause the LEDs to light. So you'll actually get them strobing at 120Hz. The eye can't see changes past 100Hz, so no problems there.
  
  Grab.
33. Re:110/230V AC by Grab · 2004-07-25 21:33 · Score: 1
  
  Any nay-sayers tout the dangers of DC, they need to consider the stunningly dangerous, should-never-be-allowed hazard of the battery in their car... :-)
  
  Grab.
34. Re:110/230V AC by amorsen · 2004-07-25 21:54 · Score: 1
  
  DC doesn't lose more than AC; in fact just the opposite. However, 12V does of course lose more than 110V. 12V is probably not enough for a useful circuit through the house; anything more than say 20A breakers would be too dangerous and that only gives you 240W. 24V or 48V would probably be better -- you could use cheap and efficient DC-DC "transformers" to get 4/6/9/12V according to what each appliance needs.
  
  --
  Finally! A year of moderation! Ready for 2019?
35. Re:110/230V AC by rco3 · 2004-07-26 02:07 · Score: 1
  
  Ah, but the series capacitor is a capacitive load, which will change your power factor in the direction AWAY from the inducitve loads...
  
  --
  
  Ce n'est pas un vrai mouvement de robot!
36. Re:110/230V AC by rco3 · 2004-07-26 02:13 · Score: 1
  
  You're right, of course; there has to be a diode in each direction. It's been a while since I did mine. I recall having used a small switching diode for the reverse in mine, but you could easily get away with a pair of back-to-back LEDs in parallel. You definitely don't want large reverse biases on an LED, it'll get unhappy.
  
  --
  
  Ce n'est pas un vrai mouvement de robot!
37. Re:110/230V AC by rco3 · 2004-07-26 02:15 · Score: 1
  
  Exactly correct, I'd forgotten about the second LED in reverse parallel with the first. Been a while since I built that thing!
  
  I also note that some guys on the web are also using a series R to limit inrush current on startup.
  
  --
  
  Ce n'est pas un vrai mouvement de robot!
38. Re:110/230V AC by HaveNoMouth · 2004-07-26 04:45 · Score: 2, Informative
  
  The reason AC is used because it's easier/cheaper to efficiently step up (and down) the voltage to useful levels, as per your power transmission example.
  Exactly right. The real issue is that transmission lines are not perfect conductors; there is always some small resistance which causes power to be lost in heating up the wire. The heat loss is given by the square of the current times that resistance. Therefore, you want to transmit power with as low a current as possible to minimize the power lost along the wire itself. Lowering the current necessarily requires raising the voltage if you want the same power to come out the other end of the wire, thus power is most efficiently transmitted at high voltages and low currents. This is just as true for DC as it is for AC, but AC allows you to easily step the voltage back down again for use at the load.
  If we had superconducting transmission lines--which could become commonplace this century--the whole issue would become moot because we'd be able to efficiently transmit at high current and low voltage and DC would be just as practical as AC (if not more so because of the lack of AC radiation effects mentioned by another poster).
39. Re:110/230V AC by jazman · 2004-07-26 05:57 · Score: 1
  
  > Connect 24 LEDs in series to a 120 volt line and each sees 5 volts!
  
  Yes, but only a retard, or a marketing droid, would set them up that way. One goes out - they all go out. Set them up in parallel and you get to see exactly which one died.
  
  Of course if it's a unit of 24 LEDs that's only replaceable as a unit then that might make sense. Still, you're binning 23 good LEDs which seems a bit of a waste, and 23 LEDs will give nearly as good light as 24 and may even, depending on the application, still be usable with a relatively high proportion of the LEDs dead.
40. Re:110/230V AC by Anonymous Coward · 2004-07-26 13:24 · Score: 0
  
  I've got xmas lights that are made of two strings/circuits of LEDs. The pair of circuits blink at 120Hz, but by itself, each circuit is still blinking at 60Hz. Every time I shift my eyes around or move my head I see the trace of blinking lights persist in my vision. Pretty annoying, to me anyway, but I doubt other people care or even notice for that matter.
  
  When using pulse-width-modulation to change LED brightness, I find that a frequency of 1000-2000Hz is usually sufficient for a reasonably smooth look. It's only noticeable in peristence of vision for low duty cycles anyway.
41. Re:110/230V AC by lachlan76 · 2004-07-26 23:53 · Score: 1
  
  It's madness that each lightbulb will have to contain it's own little transformer
  
  You mean like 12v Halogens? They seem popular enough. And remember, it isn't the voltage that causes problems (to a point), it's the power that is dissipated. Ohms law says that Current = Voltage / Resistance. If you increase the voltage, so will the current. When you increase the voltage 2V, the current increases 2I. But the power dissipation increases n. So when you increase the voltage, as long as the current stays low, it won't be damaged.
  
  And if necessary, you could just use a switchmode power supply to power many LEDs.
42. Re:110/230V AC by Anonymous Coward · 2004-07-27 03:42 · Score: 0
  
  Wrongo! You can run LEDs at line voltage 120V. All you need is a resistor in series with the LED so that voltage drop is with the operating range of the LEDs. LEDs can easily be manufactured with a built-in resistors to operate using normal AC line voltage ( The only additional hardware would be needs is a full wave bridge recifier to reduce flicker).
43. Re:110/230V AC by Canis+Latrans · 2004-07-27 07:02 · Score: 1
  
  If that's the case, then it seems to make sense if everyone just has a central DC transformer in their house. These days, everyone probably owns about 10-20 DC transformers already (every time you buy a phone, answering machine, recharger, computer speakers, or just about any small piece of digital electronics you get one). It's kind of wasteful that we have so many of these things kicking around all the time; why not just have a central one for the entire household?
44. Re:110/230V AC by Sparr0 · 2004-07-28 09:40 · Score: 1
  
  the electronics required to lower DC voltage, safely and handily, are insanely simple.
All heat, no light - sound familiar? by Mordant · 2004-07-25 04:11 · Score: 1

Just think what this could mean for online forums in general, and Slashdot in particular! ;>
Professor Hubert Farsworth by baywulf · 2004-07-25 05:23 · Score: 1

Good news everybody. I just invented a new gadget. An integrated reflector that could lead to ubiquitious LEDs.
Re:Professor Hubert Farnsworth by Dachannien · 2004-07-25 05:39 · Score: 0

Wernstrom!
I want a LED lighted DLP projector by doc+modulo · 2004-07-25 07:06 · Score: 2, Insightful

At the moment, projectors are lighted by expensive, proprietary light bulbs.

Because of the hot bulbs, the projectors are too noisy to enjoy a nice movie night at home and they burn out after a while.

An array of LEDs would be superiour because they'd be more durable (no need for expensive replacements after X hours) and might be cool enough for fanless beamers.

Unfortunately the manufacturers use the projectors like razorblade holders or like inkjet printers. You can only fit the replacement bulb that the manufacturer made themselves and the replacement bulbs are very expensive because of that monopoly.

However, all it takes is ONE monufacturer to produce a good LED beamer to disrupt the current situation. All the others will have to follow if they want customers after LED lightsources take over, the sooner the better.

I made up my mind to ONLY buy a LED beamer because I know it's possible and I know I'll be screwed over by the current beamers if I don't. The less bulb-beamers we as consumers buy, the faster the changeover will happen.

--
- -- Truth addict for life.
1. Re:I want a LED lighted DLP projector by darkjedi521 · 2004-07-25 07:43 · Score: 1
  
  The projector lamps are all standard. Where the manufacturer is gouging you is for the integrated reflector. The style of discharge lamp used in projectors tends to have a single hotspot that needs to get focused to get optimal illumination. Misfocusing the hotspot can lead to most of the light not being reflected into the picture element, or too much heat being reflected into the element, burning out the LCD/DLP/film/whatever. No imaging tech is immune to this.
  For an example of price differences, an XBO 2000 (2KW Xenon arc, no reflector), availble from several manufacturers runs about $600 a piece. Conversly, a 300W lamp/reflector combo for an Eiki LCD projector runs $520 and has only a single source.
  Manually focusing a new discharge lamp in a projector is a tedious, hot process. Its also easy to heat damage elements while doing it. It was a good idea to prefocus the lamps in the reflectors and sell them that way, unfortunately, it turned into another version of printer ink cartridges.
2. Re:I want a LED lighted DLP projector by amliebsch · 2004-07-27 05:36 · Score: 1
  
  An inexpensive array of LED's that could possibly emit enough such light is a fool's hope. Now, solid state RGB lasers that rapidly scan the entire screen CRT-style may soon be feasible...
  
  --
  If you don't know where you are going, you will wind up somewhere else.
3. Re:I want a LED lighted DLP projector by Aidtopia · 2004-07-27 05:38 · Score: 2, Interesting
  
  Despite the naysayers here, you could be on to something.
  
  A DLP projector uses a "white" bulb and reflects the light through red, green, and blue filters. The filters (ideally) are band pass filters, allowing only a fraction of the light to pass, and absorbing the rest, which must be reradiated as heat.
  
  If our light source was "tuned" to put most of its power out in the bands used by the filters, then a lot less light would wasted. So if you could make your light source from properly tuned and bright red, green, and blue LEDs, it would be much more efficient, requiring less power and creating less heat. I'm sure the details of this make it hard to solve, but in theory it would be a great solution.
  
  [Are LEDs different colors because of the filtering of the packaging or because they're tuned to produce different wavelengths of light?]
  
  DLP projectors have two basic designs. Most reflect the light off the mirror matrix and through a rotating wheel of red, green, and blue filters. Some high end ones start with three light sources (or a single source that's split with prisms). The three light sources are filtered and then bounced off independent mirror matrixes and recombined with prisms.
  
  Both of these could benefit from an LED approach. With a single matrix, you could get rid of the mechanical color wheel by strobing the LEDs instead (switch them on and off in R-G-B sequence). I believe, (though I'm not certain) that LEDs turn on and off very quickly. With three matrixes, you simply start with three different light sources, rather than splitting a single source and losing heat.
  
  I'm sure there are many electrical and optical challenges with this approach. If they can be solved, you could make very robust, quiet, long-life, low-power DLP displays.
Similar technology available for two years by jdb2 · 2004-07-25 08:01 · Score: 1

See :

http://www.google.com/search?hl=en&ie=UTF-8&q=omro n+dr-led&btnG=Google+Search
http://www.omroncomponents.co.uk/Press/DR-LED.pdf

The above operates according to the same general idea of recovering light that would otherwise be lost, although in this case the implementation is completely different and much less sophisticated than that referenced in the post.

The manufacture claims a 2x improvement over conventional LEDs as well. Unfortunately, they seem to have suddenly discontinued the whole product line as of April for some unknown reason.

jdb2
You might be waiting a little while.... by Pinkoir · 2004-07-25 09:35 · Score: 1

Projector bulb systems typically put out light in the order of 5000-8000 lumens (although cheap ones make do with less). Even high-wattage white LEDs put out nowhere near this amount of light and so you would need a bunch of them together to get the same bright image you are used to with your noisy gas discharge system. The innovation will not increase efficiencies enough in the near-term to change this.

You won't get rid of the noise either...since LEDs require a low junction temperature to operate efficiently and since the high-wattage LEDs generate quite a lot of heat (especially given that you will need to cram a good number into a small area) you will need some active cooling to kep them from cooking themselves. Nobody wants their movie or game getting progressively dimmer as time passes after all..

-Pinkoir
1. Re:You might be waiting a little while.... by pauldy · 2004-07-25 20:48 · Score: 1
  
  You have no idea what your talking about. Your better off questioning the veracity of the statement of 99% efficiency. Given that 100% efficiency is somewhere around 220 Lumens/Watt your looking at a tops of 40 watts to generate the light required to exceed your estimate of 8000 lumens. But don't forget that 99% of that energy is being converted into light. The actual heat energy is somewhere in the neighborhood of 1/2 a watt. This easily qualifies for fanless operation. That being said I am skeptical of any tech story like this that appears on slashdot anymore. They are always looking for funding for patents or development.
2. Re:You might be waiting a little while.... by GregAllen · 2004-07-26 11:20 · Score: 1
  
  Your == possessive. You're == you are.
  
  You're awfully inflamatory. The LED is not 99% efficient -- the reflector inside the LED is. Typical white LEDs are well under 40%.
  
  --
  Please help find my missing daughter: FindSabrina.org
DC power transmits *better* over long distances by Anonymous Coward · 2004-07-25 11:46 · Score: 1, Informative

That's why it's used for the highest-power and longest-distance links, such as the lines from northern Quebec to New York.

AC lines radiate like antennas. 1/4 wavelength at 60 Hz is 776 miles at c (in practice, reduce by the appropriate velocity factor), so if a transmission line gets long enough, it can radiate a lot of power.

What AC is good for is *conversion*. For long distances, you want high voltages, and transformers are a simple, reliable, and cheap way to convert from a high transmission voltage to a low use voltage.

The only way to change DC voltages is to chop it to AC first. This may be done inside a motor-generator (commutator) or a switching power supply (switch), but either way, you're converting to AC.

Doing this at multi-megawatt power levels gets a bit tricky. It's only worth doing if the savings in power (reduced losses) and copper (you don't need to carry the current that isn't getting lost) make it worth the expense.
Increasing solar collector efficieny? by Randym · 2004-07-25 15:16 · Score: 1

"In an LED, light emits from inside the semiconductor in every direction, but our omnidirectional mirror reflects light equally well no matter what the angle of incidence. Other types of reflectors are only efficient when the angle is normal, or 90 degrees perpendicular to the surface," said Schubert.
I wonder if this technology could be used to enhance the efficiency of solar collection devices. This reminds me of the way that plants collect and use photons. Any solar engineers out there?

--
DNA is a Turing machine. You, however, being dynamic and emergent, are not.
1. Re:Increasing solar collector efficieny? by OOO0000OO0O0 · 2004-07-25 15:40 · Score: 1
  
  I'm not a solar engineer, but I have a suspicion that the power you get depends on the watts/area you get on your solar cells. You could get greater watts/area using this new reflection technology. A bunch of mirrors can concentrate the sunlight with greater efficiency. However, it remains to be seen just how much of a percent increase in watts/area on solar cells this will engender. Given that this is an "omnidirectional mirror", you could have your collector array operating at peack efficiency for a much longer period per day.
2. Re:Increasing solar collector efficieny? by hcdejong · 2004-07-25 21:21 · Score: 1
  
  An omnidirectional mirror will not magically reflect the light in the direction you need (ie where the solar cells are), so you still need move the mirror during the day. These omnidirectional mirrors wouldn't be an improvement over current technology.
leDIODEs by leonbrooks · 2004-07-25 16:10 · Score: 1

the D in LED stands for diode
Unfortunately, they're not very good diodes, with the reverse (blocking) voltage typically not being much more than the forward voltage. What this means in practical terms is that unless you also have a real diode in series with the LEDs (or a varistor/series-pair of zeners across the LEDs), the first power surge along will kill them.

Your 120VAC (our 240VAC) is not constant. It goes from zero to root-2 of the voltage. This causes immense problems with movement, particularly machinery running at an exact multiple of the mains frequency (as some kinds of motors do). Running your LED strings three-phase would help to mitigate that, but it'd be much simpler to put the little suckers behind a small but robust bridge rectifier and a pair of resistors teed across a modest but high-voltage capacitor. And of course, modern electronics being what they are, there is probably a "one-chip" (generally requires at least a coil and capacitor as well) AC-DC converter around that costs peanuts and would do the job.

--
Got time? Spend some of it coding or testing
colour temperature by RMH101 · 2004-07-25 23:15 · Score: 2, Interesting

but bear in mind the colour temperature of them seems "weird" to the human eye; lighting a room in them isn't very cozy.
1. Re:colour temperature by joebok · 2004-07-26 05:14 · Score: 1
  
  Flourscent lights also have a "weird" color temperature - but improvements have been made and we got used to them.
2. Re:colour temperature by Noofus · 2004-07-26 06:21 · Score: 1
  
  Cant be any worse than flourescent lamps. I cant stand the things myself and hate having to be under them 8 hours/day.
  
  Incandecent bulbs bay ultimatly be yellow in color but they *feel* better. In any case I bet there would eventually be LEDs that are capable of emitting full spectrum light, not just white...
Actually I do... by Pinkoir · 2004-07-26 00:30 · Score: 3, Informative

If you read the article you will see that there is no claim on 99% efficiency of the LED. The claim is 99% efficiency on the reflector. No LED anywhere in the world comes even close to 220 lumens/watt. The best I've seen in the real world is about 80 lumens from the 3 watt Luxeon devices put out by Lumileds. These devices are very hot and need a lot of heat-sinking to avoid destroying themselves in any confined application. You have to remember that LEDs aren't magic. They are just full of inefficiencies and the back reflector issue is only one of them. I work with high intensity white LEDs every day and if you know of some that can give the output you talk about that don't need active cooling for God's sake tell me where I can buy them.

-Pinkoir
1. Re:Actually I do... by pauldy · 2004-07-31 17:18 · Score: 1
  
  I am guilty!!! Please direct the comment of knowing what one is talking about to myself and whomever posted this story. I only read the story header, which does claim that they raised the efficiency of leds to 99%. I don't know why I even bother reading slashdot anymore I'm guessing I should spend more of me free time elsewhere.
LED traffic lights by Latent+Heat · 2004-07-26 03:15 · Score: 1

My take on LEDs is that their efficiency (lumens/watt) is about the same as an incandescent light bulb, but the LED throws its light in a narrow cone while the light bulb throws its light in all directions.
When the application is putting the light in a narrow cone (i.e. traffic light), the LED comes out on top because the light bulb requires a reflector housing which is far from 100 percent effective in getting all the light to come out in the front. And as an added bonus, the LEDs last so much longer so you don't have to send crews out to change bulbs.
When the application is lighting a room, LEDs offer little or no efficiency advantage. For efficiency, the newer types of fluorescents (electronic ballast, T-8 bulb) are as good as it gets unless you go into some exotic tech or are willing to tolerate pure yellow light.
Two words: Track Lighting by Anonymous Coward · 2004-07-26 06:43 · Score: 0

I have recently installed track lighting at my house and it's the sort that has a transformer that transforms line voltage before the track.

(Some varieties do what you mention and transform at each individual light).

This one transformer runs 12 Xenon fixtures.

But it's not hard to imagine (and defintely not madness) to assume a drop in incandescent replacement with integrated electronics. I've already got a house full of compact flourescents...each of which has an integrated ballast.

I would pay $10 a bulb for a bulb that saves me money and never needs replacing.
Why not go the whole hog? by Engineer-Poet · 2004-07-26 06:49 · Score: 1
You can get rid of all those problems easily.
1. Rectify, filter and chop the incoming AC.
2. Feed chopped AC into a small transformer which changes it from the filter output voltage to the voltage required by the diode string.
3. Run this at ~20 KHz so that flicker is invisible.
If you run the switcher to get a specified level of current through the LED string, you can both vary the brightness to spec and run at any voltage within the capability of the switcher. I don't see a big market for internationalized light bulbs, but it would be possible.
--

Sustainability and energy independence essay
Yes, you'd set them up as a string. by Engineer-Poet · 2004-07-26 06:59 · Score: 1

The usual drop on a red LED is about 1.7 volts, so a string of 24 would have a working voltage of about 41 volts (yellow and green have higher forward voltages IIRC). You are going to need a power supply to run this, and it is going to be much easier to generate 41 volts @ 200 mA for a single series string than 6.8 volts @ 1.2 A to run 6 parallel strings of 4. For the hypothetical traffic light the "supply" could be as simple as a diode bridge and a current-limiting resistor; that resistor would run mighty warm but it would generate less heat than the bulb it replaces.
One goes out - they all go out. Set them up in parallel and you get to see exactly which one died.
Repair is so expensive compared to replacement that it doesn't matter. The repaired unit would not be sealed as well as the original, plus it would have been stressed mechanically and thermally as part of the repair process. Why would you pay more for a unit that is less reliable than a new one? You wouldn't.

--

Sustainability and energy independence essay
Reflectors change the efficiency by Engineer-Poet · 2004-07-27 02:10 · Score: 1

Fluorescents are perhaps 30% efficient. If reflectors can nearly double the light output of LEDs by using light that would otherwise have been absorbed by the back, the LEDs could beat the efficiency of fluorescents.
This is not as difficult as it sounds. Fluorescent lights have two conversion stages (electricity to UV in the mercury vapor, UV to visible light in the phosphors) and each conversion has losses. LEDs have only one, which gives the LED an inherent advantage.

--

Sustainability and energy independence essay
1. Re:Reflectors change the efficiency by cmowire · 2004-07-28 08:31 · Score: 1
  
  No, White LEDs have two stages. Electricity to Blue/UV in the chip, UV/Blue to White in the phosphors. Except that the mercury-argon arc is more efficent than the LED chip so far at producing Blue/UV light. In both cases, mind you, the base device does produce a certain amount of visible light as well.
  
  LEDs are decent for some single-color applications (although cold-cathode "neon sign" tubing often does just as good of a job), low-voltage, and under some mechanical-shock requirements.
  
  Add to this that LEDs are an order of magnitude harder to manufacture and you start to realize that it's going to be a while before LEDs are worth it.
  
  Also note that the reflector is not a miracle worker. Usually, you want something more than a point source with a very small throw angle if you want illumination. And they can always be integrated into the casing of a flourescent, the same way that some of the existing flourescent ceiling fixtures are.
  
  --
  Gentoo Sucks
LEDs replacing all lights? by Ced_Ex · 2004-07-27 03:04 · Score: 1

But can LEDs be dimmed to get mood lighting? Hmm... I bet all you Slashdotter failed to think of that scenario.. haha...

--
Live forever, or die trying.
1. Re:LEDs replacing all lights? by Anonymous Coward · 2004-07-28 15:59 · Score: 0
  
  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>