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    What Is The State Of Solid State LED Lighting?
    By Chris Rollins | December 29th 2008 02:12 PM | 41 comments | Print | E-mail | Track Comments
    About Chris

    Chris Rollins is a recent graduate in aerospace engineering from Cal Poly, San Luis Obispo. When he's not snowboarding, he's writing about or researching...

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    It seems like they're already everywhere - if you look down at your keyboard, one is providing the little green indicator for your Num Lock key, while another may be frantically blinking to inform you of your waiting voice mail. On your next drive, chances are you will stop at a stoplight lit purely by LED's and perhaps may notice a blinker made up of small, bright lights instead of one bulb.

    LED's certainly are everywhere, faithfully providing indications of all kinds. But, with a few exceptions, the primary purpose of an LED is to indicate rather than illuminate, despite the fact that LED's do nothing useful besides produce light. A few new developments, however, may bring solid-state lighting into our homes very soon.

    Little, but Bright: LED's may be poised to replace incandescent and compact fluorescent bulbs as our home or office light source. Photo Credit: MIT

    An LED, or Light Emitting Diode, is a type of circuit element that emits light when electrical current flows through it in the appropriate direction. Like a normal diode, current flow is blocked when it travels against the direction of the diode. When a positive voltage is applied to the positive side of an LED, the electrons that flow are required to jump down in energy as they cross the diode - emitting the lost energy as light. This light is generated at one specific frequency, based on the characteristics of the materials used. When creating white light that may be useful for lighting, however, a blending of many colors is needed - something the LED does not seemed easily poised to accomplish, despite numerous advances in LED technology.

    Red light was the first visible light LED to be produced, in 1962, followed by yellow and green. Much later, in the early 1990's, blue-spectrum LED's were developed - a huge advance in usefulness, since blue light can be combined with red and green to make white light. However, this approach was inefficient, and companies were scrambling to make a single diode that could produce white light on its own. Then, in 1993, a company named Nichia created the first white LED using a blue LED with a phosphor coating. The coating was the trick - it provided enough shifting of the light wavelength coming from the diode itself to create white colored light.

    Why, then, aren't we using LED's - which are much more efficient than either incandescent or fluorescent bulbs - to light up our homes and offices? The major problem, of course, is cost. Current white LED's require a substrate made of sapphire and an additional mirroring layer to reflect light that would otherwise be lost. As a result, LED lights already on the market cost approximately $100, far too much for the average consumer.

    Researchers at Purdue University have found one method of significantly reducing the cost of a white LED by eliminating the expensive layer of sapphire. Instead, they used silicon as the substrate (the material the diode is printed on) and zirconium nitride as the reflector. This had never been done before, mainly because silicon reacts with zirconium nitride and changes its properties. The researchers solved this by putting a layer of aluminum nitride between the silicon and zirconium nitride.

    "One of the main achievements in this work was placing a barrier on the silicon substrate to keep the zirconium nitride from reacting," said Timothy D. Sands, the Mary Jo and Robert L. Kirk Director of the Birck Nanotechnology Center in Purdue's Discovery Park.

    Reactor: Timothy D. Sands, left, watches over a reactor that deposits gallium nitride on silicon at a temperature of 1000° C. Photo Credit: University of Purdue

    Silicon also provides a crystalline structure that the other materials conform to when deposited on the substrate. 

    "We call this epitaxial growth, or the ordered arrangement of atoms on top of the substrate," Sands said. "The atoms travel to the substrate, and they move around on the silicon until they find the right spot."

    Crystalline structure is very important to the efficient working of an LED - if the materials used to create the LED were sprayed on glass, for instance, the LED would operate very inefficiently. Using silicon also reduces cost by allowing industry to scale up, or create large batches of LED's on large wafers of silicon, something the semiconductor industry is already good at.

    LED lighting holds many advantages over traditional lighting, most notably in efficiency. "If you replaced existing lighting with solid-state lighting, following some reasonable estimates for the penetration of that technology based on economics and other factors, it could reduce the amount of energy we consume for lighting by about one-third," Sands said. "That represents a 10 percent reduction of electricity consumption and a comparable reduction of related carbon emissions." LED's are also more durable than incandescent or compact fluorescent bulbs, and have the added bonus of being devoid of mercury - a chemical found in compact fluorescent bulbs that makes them difficult to dispose of.

    E. Fred Schubert, a professor of electrical engineering and physics at Rensselaer Polytechnic Institute in Troy, NY, recently published a paper where he describes the coming revolution of solid-state lighting. "Replacement is fine," he says. "But we must look beyond the replacement paradigm to see the true benefits of LED lights." Schubert imagines large panels that are able to control all aspects of lighting for a room, far more than simply "on" or "off." With cheap LED's available, many different wavelengths could be created in a room and blended to produce specific effects, like an accurate representation of sunlight at different periods of the day. This is important, since current white LED's produce a harsh bluish light that people generally don't like to use when doing normal indoor activities, like reading. The ability to control the hue and saturation of light is something many consumers may find appealing.

    The way the industry is booming, Sands expects that we will have LED lights within 2 years. There are still technical hurdles, but he expects industry to clear them easily. "These are engineering issues," he said. "Not major show stoppers."


    nice post

    Kimberly Crandell
    I'm happy to hear there is another option on the horizon that will provide the efficiency of CFL's, without the environmental hazard of mercury.  Plus, sounds like there is a much broader potential in use and application of LED's.  The future looks bright!
    Kim, you are one hot mama!!

    Let's see some more pics of you!

    As the reduction of power needed by residential demands continues, due to innovations like epitaxial growth LEDs, the portion of the residential energy budget that can be fulfilled through renewable energy, as a ratio of the total, should increase dramatically.


    I find this post ironic. The thing is, we already have LED -bulb- replacements, since over a year, that emit equal lumen at 1/3rd to 1/5th the power consumption of a CFL equiv., and they are not at a $100 cost - they range from $20 to $30. I have no idea how the availability is in the US, or the UK, but these are obtainable in a multitude of shops in the nordic country I live in.

    I have LED bulbs in a few locations in my house. The bulbs that provide light equivalent to a 60 watt standard bulb ARE $100. I have the $30 version and they are simply 'not ready for prime time'. They produce a sickly yellow-green light that is barely equivalent to a 15 watt standard bulb. We have one in the hallway as a night light... two in a closet and that's about it. While it is extremely cool that they only use 2.5 watts, they're simply not practical replacements for primary lighting.

    While LED technology is getting all of the "buzz", there is another, almost overlooked, technology that is currently more energy efficient then LEDs and almost all commercial lighting technologies - magnetic induction lamps. LEDs presently offer conversion efficiencies of between 35 and 55 Lumens/Watt [LEDs with efficiencies of up to 80 L/W are just coming to market and are still prohibitively expensive].
    Magnetic Induction lamps offer efficiencies in the 67 to 90 Lumens/Watt range with higher wattages being more efficient. Lifespan is also similar to LEDs in the 65,000 to 100,000 hour range. Even low wattage induction lamps produce 20% more light than CFLs of the same wattage and offer 3 to 5 times the lifespan. Induction lamps scale well with increased lifespan and efficiency as the wattage increases while LEDs do not scale at all since higher outputs are created by using an array of LEDs, thus the efficiency is limited to the most efficient LED in the array.
    For those unfamiliar with magnetic induction lamps, I have an article available on Google Knol at http://knol.google.com/k/l-michael-roberts/how-induction-lamps-work/2q45...

    >>despite the fact that LED's do nothing useful besides produce light.
    I know of one other use. LEDs are used in some guitar preamps. Some feel that the clipping is softer than with typical diodes, and comes closer to the sound of a overdriven tube. The Carvin TN100 is one preamp that uses LEDs.

    Other LED lighting uses are headlights and street lights. The military has been using LED headlights on certain vehicles in Iraq for over a year (Truck-lite) and may have USDOT approval soon if not already. Minnesota and now New York and other cities are trial testing LED street lights. The military and many police forces have high power LED flashlights. I have one of the smaller ones, about the size of a mini mag, that uses a single white LED and produces blinding light that has about 100 yard range (Surefire flashlight). The military has a much larger version that can illuminate a battle field if they so choose. I've also seen various LED accent lighting in large home improvement stores and I've see higher output light bulb replacement LED's for about $40-$50 online. My motorcycle also has an ultra bright LED taillight. LED's are coming sooner than you may think. And should be cheaply available (IMHO) as light bulb replacements before the CFL bulb mandate kicks in in 2012.

    Chris Rollins
    They're certainly coming - the only problem is, the light they generally produce is bluer than the light we're used to seeing in our homes. It's great for applications like headlights or battlefields where great detail is important. Most of us aren't really interested in seeing that much detail in our own faces before our morning coffee, for instance.
    http://www.hplighting.com.tw/ produces cool-white, warm-white and natural-white LEDs

    Nearly all light bulbs in our house are now LEDs. For corridor lighting the slight blue cast that used to be found is not a real issue. More recent LED bulbs I have bought have a far more natural appearance. My main complaint about the cheaper LED bulbs is the level of illumination provided or the narowness of the cone of illumination. To overcome this I have, in the kitchen, used a CFL or two alongside some of the LED bulbs. A room that was previously illuminated with 300W of incandesent bulbs and was then illuminated with 54W of CFL bulbs, is now iluminated with 27W of LEDs and my mother (age 77 and usually quite resistive to change) who is staying with us for the first time since the LED lighting was installed hasn't complained about either the colour or the level of illumination.

    I've been puttering around with LEDs for area lighting in various configurations since '98 and I've got to say, I find this article pretty underwhelming. As Markus points out above, the prices and time to market in the article are way off. I've found, for example, that I got perfectly acceptable light for a hallway and kitchen area (though not as bright as I would want given my budget of thirty bucks) by wrapping amber and white LED holiday light strands around each other along the ceiling. I found years ago that a combination of white LEDs and a candle or oil lamp or two gave beautiful light in a bathroom. That was my typical lighting in that room for over five years, which tells you how old my LEDs were. Current ones are even better. I've tried several other "cocktails" of LEDs with halogens, incandescents, and so on and I've found that it's key to remember that they don't need to be the sole source of light to cut energy usage and increase flexibility. FEIT's line of "nightlights" show some of these options very well.
    LEDs set up to run directly on lower voltage, DC current, which is, of course, what most actual diodes "want to" run on anyway, should be ideal for lighting that isn't attached to the grid at all. A typical medium sized solar panel generates about 12 volts, which is then fed into a 12 volt or 24 volt battery system. Such a battery system could drive lighting in a house where the only "disposable" parts are the batteries, with "disposable" being measured in years. For areas like entryways, hopefully it will eventually be possible to buy something like a mat of piezos built into a "rug" that generates enough power from the people walking on it to drive most or all of the lighting for that area. Again, a grid connection would be not only unnecessary, but wasteful. Running LEDs on 110 AC just forces wasteful stepup and stepdown, not to mention rectifiers and other "make-dos" that a 12V DC system needs not at all.
    Another thing to look at is the "overclocking" being done to LEDs to achieve performance characteristics beyond what the makers had in mind. Sadly, the only detailed charts and numbers I've seen on this have been in magazines meant for pot growers. NASA is using blocks of red and blue LEDs to make very efficient grow lights and the spread of those, too should drive down costs.
    Which brings us to Moore's Law. LEDs, though not perfectly, do gain from the stunning progression we have seen in all devices made of semiconductors, as the passage of time brings constant increases in power delivered, decreases in power used, and decreases in price. With laptop makers investing hundreds of millions of dollars, if not billions, in improving LED performance so that they can better be used for backlighting screens or even as the screens themselves, we can guarantee that whatever performance numbers we see now will, well, pale besides what is coming in the next few years. As the new NYC streetlight designs show, we may be best served for now by ramping up and testing not monolithic units but rather lights in which the blocks of LEDS can be swapped out as they improve without having to replace the whole fixture.
    LEDs have the potential to change our world. But they will only approach that potential when we realize that they are no more "incandescents, but better" than cars are "horseless carriages". Talk to any recent graduate of a good industrial design program and they'll be able to tell you some of those potentials in great detail. But trying to judge based on an article like this? Not such a good idea.

    Great point,

    LED's are the answer, but it would make far more sense to operate them on 12VDC rather than conventional 120VAC of most homes and businesses. As mentioned, this would be ideal with a small solar and battery system, so more adapt to bulding this system into new construction which is what we are working on. Wiring for 12VDC lighting is not difficult given the light wiring is little different than the old hard wired phone jacks.

    As to adapting existing lights, it would not be that difficult, and with long term savings and logevity of LED lighting, you may never have to replace a light again. I have been running 12VDC LED for 8 years with not a single failure, and since they draw so little electric, you could easily light your home with a simple HD 12 volt car battery even without solar, just plug in trickle charger which is what I have been testing. After all, how many lights do you have on at one time in the average home. I have been running blue LED's as a back up lighting sourse for a couple years when power goes out, and since 12VDC LED prices are less expensive now that many auto manufacturers are going with LED headlamps, so I am sourcing these to convert my blue LED power outage system to regular lighting in near future, all on 12VDC, now if I could only figure out how to heat home on LED's. lol
    I just bought a 3 pack of 40 watt LED bulbs at SAM's club for $14.

    3 for $14 - LED's are here now.

    On box usage 40 Watts = 1.5 watts...

    Wow, I nearly fell over when I saw them.

    What next? what is your experiance with it? i also have one which directly operate on mains and gives comparable lumens of 18 w CFL and consumes mere 6 w or so pl give feedback of your experiance

    My brother owns a manufacturing/assembly unit of LED street lights for atleast 2 years now. They are definitely a bit expensive and brighter than needed for normal use.
    They work great for shop lighting, focus lamps, street li
    As a an amateur (and sometimes professional) videographer/filmmaker I have been using LEDs as on camera lighting for almost 3 years now. LEDs put out bright light without drawing too much power so I can use my VC's battery to power them. The ones I have are fully dimmable too. Try doing that with a CFL. They're really light and don't generate any heat either. And now since the price has come down so dramatically I started buying bulbs to use at home. I don't have them everywhere in my house because they tend to be "spotlighty" and don't cast light like regular bulbs do. Do a search on ebay for led lightbulb there's plenty of them available and they're affordable.

    The price quoted in this article is grossly inadequate. Is the author a shill for PG&C? There's an LED bulb on amazon.com for $9.00, but around $20 is average. Get your facts straight before scaring people away from this efficient and inexpensive lighting option!

    Bring the manufacturing of the LED to to the states, EU, and Canada. Do not use Mercury or lead. Sell it as made locally. They will take over CFL's within a year.

    Chris Rollins
    Well I'm certainly not a shill for PG&E, nor was I trying to downplay the benefits of LED lights or scare people away from them. Really, I just wanted to know myself when I could expect them to become competitive and really grab a large share of the market, so I decided to find out. The 2 year figure quoted in the article pertains to the point when the researchers at Purdue estimated that LED lights would be competitive with current lighting options - because let's face it, a $20 light bulb is still way too much for most people.

    As for the $100 price point, that also came from the Purdue researchers. I think they may have been talking about single-LED light bulbs with similar luminosity as incandescents or CFLs. Obviously, most LED bulbs have arrays of less efficient LED's, which is more economical at the moment, but I think the researchers mostly wanted to compare their new technology to existing technology. Either way, it's still a big improvement.

    I'm all for LED lights, and I'm glad so many people here are early adopters.
    I refute it thus:

    We're changing over slowly and steadily, starting with evening "low blue" reading lights all over the house.

    It'll be a while before the big cheap 4x4' T-12 fluorescent troffers get replaced, but it'll come.

    Will you please emit light into my diode?

    So many bones to pick with the article, and some of the comments, but I just want to point out one thing:

    There's a common misconception that "bluer" lighting is somehow "sharper" or "better." This is false.

    There was a nugget of truth to it when halogen lighting first became available - regular incandescent bulbs have an extremely "warm" cast (most energy towards red and yellow, less in the blue spectrum), so moving a notch closer to daylight could be some improvement. Note that these new lamps still were not even as "blue" as daylight. In fact, even daylight-balanced bulbs can be useful in specific applications, but there are two things to be aware of:

    Out of the spectrum, humans have the least visual acuity to blue, see this reference or many others. We have fewer blue-receptive cones in our eyes, so the images we perceive in blue light have a lower resolution than with warmer colors. Blue's "sharper" wavelength allows tighter detail when, for instance, a player reads a Blu-Ray disc, but not in the human visual system.
    If that weren't bad enough, we perceive more glare with blue light for that and other reasons.

    So, blue light is less flattering in the morning not because it brings out the crags in your face, but because it makes it harder to see them -- and leaves us squinting, whether we realize it or not. (There are also psychological reasons to prefer warmer light; it's more familiar to us after years of firelight and incandescent lighting, but also brings out the 'warmth' in our skin. Under daylight, if someone looks blue, they're probably ill, a corpse, or visited a very creative tattoo artist.)

    So there are very real reasons to prefer a "warm white" for indoor lighting, especially if you're going to read or do fine work under it, and thankfully the LED manufacturers are starting to offer products with a range of casts from "warm" to "cool."

    Meanwhile, please resist the urge to upgrade your car's headlights to 9000K wannabe-HIDs; yes, they'll highlight every drop of water in the air, and look more blinding than the sun, but they won't help you see any better (or me see any better after I've glanced into them). Try a set of yellow bulbs with the same light output and you'll find that you can see better even though they appear much dimmer -- and without ruining your night vision, so things *outside* of the light are still visible. (Similarly, this is why daylight-balanced streetlighting is often a bad idea; warmer light looks dimmer at the same output but also lets us see into the shadows.)

    I tried one of those bulbs. It was supposed to last maybe 20 years. It lasted two months. Flickered for an hour or so, then was burnt out. What gives?

    My mom has 6 recessed lights, lighting her kitchen. She has been complaining for months that she's constantly changing the burnt out bulbs. I bought her an LED Light bulb as an experiment. She's had the bulb for about 5 months and 3 of the incandescent bulbs have burnt out since then, but the LED bulb is still going strong. She says she wants to change all of the bulbs to LED. I find the color to have a little too much blue, but I know that there are warm white bulbs available.

    She now wants her undercabinet lights to be LED. I know they sell LEDs in a strip. I'll try ebay?

    I’ve been replacing my old bulbs (incandescent and CFL) with LEDs to be Green and save money. I’ve had a very good experience with LEDInsider.com. Good selection, excellent customer service, fast delivery. I just want to share them with the rest of you. Buy LEDs and Go Green!

    Thanks, I'm going to take a look at them.  I found  leddistributors.net they have some bulbs and LED's on a strip. Their prices are pretty good.

    Could I please have a LE light that will give me a broad spectrum of light so that I can grow indoor plants better?
    Something that will fit into normal domestic 240v fixtures would be nice


    The "holdup" is semiconductor processing technology. The same reason the solar cells are expensive. It is just a matter of time when the capitolist system will solve the issues.
    What capitalist system?   Prior to last month, government already controlled 50% of all capital.   Now it's even more.   There is no capitalism when companies and people no longer have it and a central government does.
    There is a new LED that replaces a 100 watt can light. It's super bright and dimmable. Twice as bright as Cree's LR6. It is not a "bulb" but rather an entire fixture that will last for over 100K hours. There are choices in color but white is the most efficient. And it's made in the USA!


    Chris Rollins
    Pretty cool, but I don't see any prices on their website. That probably means they're really expensive.
    I too spent a few moments on the website and didn't find any prices. We are getting closer to LEDs becoming affordable. Just look how far we come so far.
    i m having a serious problem regarding failure of LEDs especially Green & blue.
    i m a quality engg. in a firm & encounters daily rejection of LEDs.
    The LEDs which were not working at 3v will work on higher voltages & after applying higher voltage they start work @ lower volatges.And which were found ok at our bench will be rejected at final stage due to not working at nominal volatge & continue work if higher volatge is applied & then start working even at lower volatges.

    i m not aware what's reason behind this !!!!!!!!!!!!!

    Plzzzzz guide me abt this problem

    Single bulb, LED lights in the Shanties American style corporatism has let us will certainly cut down on the amount pf power we steal from the county to survive the cold depression coming in with the next "Down Cycle" and further raping of the American people! Perhaps China will come to our rescue, breaking U.S. patent laws, bankrupting the patent shysters, and copying without royalties or remorse the fantastic LED technologies predicted at Cambridge University.

    Just imagine the merriment of the common folk after the commies help us throw off the yoke of capitalistic and corporate exploitation, and re write the rule books in our favor! We will drive cars with the batteries from the EV-1 once again, exxons patent rights ignored by China a much bigger force! and the World will prosper from this!
    I have purchased several under cabinet Maxim LED lighting 21 inch models. All but one has a warmer more yellow light, but one has a much more blue look. These were bought from the same lighting store at the same time. I wonder if something in the manufacturing process caused the problem. I find it interesting, but must take the one back to get the same warmth as the rest so it doesn't look odd. Is this a bigger issue than the company would let on?

    >Schubert imagines large panels that are able to control all aspects of lighting for a room...

    Greetings from The Future (13 Mar 2012)!!!
    Dear Prof Schubert: IT AIN'T HAPPENED YET.

    Hey "Future Guy"... It was done several years ago. We call them "Flat Screen TV", but there is no reason one of these could be used for lighting purposes. It certainly can do all colors of light including white.

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