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The End Of The Light Bulb?
sdmonroe wrote to mention an MSNBC article discussing the likely eventual replacement of common light bulbs by LEDs. That replacement is likely to come quicker thanks to an accidental discovery announced this week. From the article: "Michael Bowers, a graduate student at Vanderbilt University, was just trying to make really small quantum dots, which are crystals generally only a few nanometers big. ... 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.'"
Answer: there are several obvious advantages LEDs have over traditional incandescent light bulbs, they are as follows:
Low power consumption - energy saving,
Long lasting,
Cold lighting,
Ruggedness,
Small size and weight,
Fast switch times,
Simple to use.
This is from the FAQ, but it doesn't list any disadvantages..
anyone care to share?
~jennifer.k~
http://www.google.com/search?q=Michael+Bowers+Vand erbilt+University
u mdot_led.htm
http://exploration.vanderbilt.edu/news/news_quant
No, actaully, the thing holding back LEDs from practical home applications is the color of the light they produce. More specifically the color temperature.
Typical incandescent lighting comes in somewhere around 2800-3200K. White LEDs live somewhere around the 5000-7000K range. When an efficent LED source can be made at a color temperature similar to that of incandescent lighting...then you'll see it take off in as a replacement for a standard A Lamp.
This same color issue relates to the slow adaptation of Compact Flourescent lamps in homes. Only recently have they produced flourscent fixtures that have a similar color temperature to incandescent lighting.
Cost is certainly a factor...however if it LOOKS bad--meaning if it makes stuff look like crap to the average eye because it is the wrong or unexpected color temp--then people aren't going to use it no matter how cheap it is.
As lightbulbs create about 95% to 98% heat (the rest is light), and modern LEDs about 85% to 96% heat, the LEDs still create more heat than light.
reference
I'm totally surprised that they OSTG didn't pimp their LED bulb from thinkgeek. 35 bucks is a little steep though.
. htm
http://www.thinkgeek.com/gadgets/lights/7aa8/
Of course, you could always make your own.
http://www.etgtech.com/update/products/super_flux
Religion for nerds. Stuff that really matters
This could be a big advance for LEDs. But as of now, commercially available LEDs do NOT produce as many lumens per watt as Compact Fluorescent Light bulbs (CFLs.) Of course, this new LED discovery may improve LED efficiency to the point where they exceed CFL efficiency. We'll have to wait and see.
CFLs are inexpensive and readily available today. CFLs have a long life, and they save a ton of energy when compared to traditional light bulbs. Even more importantly, they don't suck like the CFLs of a few years ago that had a noticeable/painful "warm up" time.
I save quite a bit off of my energy bill by using CFLs. They really cut down on electricity consumption, and I've never had one "burn out" on me. Ever. Yet.
It is the incandescent colour that is the wrong temperature, not the LEDs. Mid-day sun is nominally 5600K, and morning/evening higher. So why do you want to emulate candle-light?
Completeness of spectrum is another issue. Cheap fluorescent tubes have huge mercury spikes and little red - maybe 55% on the accuracy scale. Good tubes achieve 95% - a marked difference. This is independent of the colour temperature.
White LEDs (at leat the ones you commonly buy today) are also fluorescent, but with pretty decent spectral accuracy. It would at least in theory be possible to build an RGB array of monochrome LEDS that would produce apparent white light.
alright, it has the white light, and none of the 'rest' of the spectrum, which apparently attracts bugs.
but yes, a narrow spectrum of white, I found a good picture here
http://www.truesun.com/Litetube.htm
roll down to where there are three bulb types listed.
note the incandescent bulb rolls up from blue to red
note the fluroscent has three spikes of blue, yellow and red
the missing bits, including the missing UV and IR at the ends, include whatever attract bugs.
so yes- a narrow band of white light......
every day http://en.wikipedia.org/wiki/Special:Random
http://exploration.vanderbilt.edu/images/news/arti cle_main/quantumdot_led_5.jpg
I just finished converting the lighting in my house to save energy, and learned a few things in the process. Most of the incandescent bulbs were replaced with compact fluorescents, but I did install 4 LED light bulbs in one application.
The current generation of compact fluorescent bulbs has come a long way from the ones I remember 10-20 years ago. They don't have the flicker or startup problem anymore, and they are available in a variety of color temperatures from 2700 degrees (yellowish, comparable to incandescent) to 6100 degrees (white, sterile). For the same light output (lumens), energy consumption is normally 22% to 27% of the incandescent bulbs they replace. They very slightly in things like color and wattage depending on the manufacturer.
Nobody who has visited my home has yet noticed the difference.
Since you can find common CF bulbs sizes for under $2 per unit (try Sams Club, etc), and they should last 4 to 8 times as long as an incandescent, the economic case is pretty sound even before factoring in the energy savings.
I replaced 4x 7.5 watt bulbs with LED bulbs and noticed a few things. The LED bulb itself is about twice as large, and as others have mentioned, the light emitted is an eerie blue-white light. You defiantly notice it. These bulbs consume 0.8 watts and produce an output pretty close to the 7.5 watt bulbs they replaced, though I could not find the output in lumens for either bulb anywhere. They were about $7 a bulb, and are rated to last 100K hours, or about 50 times as long the bulbs they replaced. Since the bulb is actually made of up 18 individual LEDs inside, I believe the rating is for the mean time until 50% of the LEDs are no longer functioning.
After converting 152 of 160 bulbs in my home, my electric bill happy.
I can make white light by emitting everything from UV to IR
or I can combine a 3 beams each of a very precise wavelength of red green and blue, and end up with WHITE.
a narrow spectrum of white.
very perception based.. I may see it as pure white, you may be more sensitive to one of the three, and therefore see it as green or blue or red tinged.
a bug may not see it at all.
every day http://en.wikipedia.org/wiki/Special:Random
Let's quote the source on that now shall we?
Isaac Asimov
"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but 'That's funny...'"
http://en.wikiquote.org/wiki/Isaac_Asimov
Hey, just thought I'd add that this site: FutureCrisis Has some really great tips on saving energy, peak oil and DIY electricity generation such as solar and wind power.
yes, here is the link to the actual article. http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/as ap/abs/ja055470d.html
Have a nice day.
I've recently converted my apartment to CF bulbs as well, and I've noticed mixed results in this regard. The Noma 60W equivalent bulbs in my hall and bedroom lighting fixtures don't exhibit this problem -- or if they do, the brightness differential is so minimal that I don't notice. They come on immediately and are at full brightness immediately (or at least as fast as I can perceive).
I also have a dimmable 100W equivalent CF bulb in the fixture in my dining room. It's a large General Electric bulb (and by far the most expensive light bulb I've ever purchased...), and it does exhibit this problem. It takes several minutes to warm up to full brilliance. However, a (non-dimmable) 100W equivalent bulb in my bedroom lamp from Noma is at perceptably full brilliance immediately upon switching it on.
Finally, I have four vanity globe bulbs in my bathroom. They are 40W equivalent bulbs from a company called "Globe", and upon turning them on they exhibit flicker and an obvious warm-up time. However, their warm-up is fairly rapid -- they seem to come on at about 50% brilliance, but within a second or so are up to 90% or so (going purely by perception -- I don't have the equipment to actually measure this). Within the next few minutes they'll be up to 100%.
There are a number of other lights here which have been converted to CF, but the above covers all the bulb manufacturers and types I have installed here. I've learned to deal with the warm-up issue in the fixtures where it's noticeable, and can live with these minor issues.
If you have such bulbs in places where safety is a concern however, you might want to consider switching brands.
Yaz.
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.
Ce n'est pas un vrai mouvement de robot!
I'm an LED flashlight geek, so I'm realistic when it comes to lighting a house with LEDs. I'd be surprised if in 20 years we weren't replacing CFLs with LED bulbs, but at the moment it's not a worthwhile investment.
Right now, I'm happy with my CFLs: for the wattage needed to light my living room and foyer with incandescents (140 watts), I can light my whole apartment on a dark October day. It's definitely a mood-lifter to not have to worry about my electric bill, or have the place look like a funeral home.
OTOH, incandescents may not be so quick to fade away: the efficiency of tungsten filaments can be significantly increased by using crystals instead of wires.
The eye can adjust to color temperatures quite well. What the CRI measures is the completeness of the spectrum, not the temperature. The color temperature is based on only the summed effect of the different frequencies. You can have vastly different spectrums that result in the same color temperature, for example in a television where only three different fairly narrow bands are used to produce a wide range of colors.
Two problems with using such narrow bands is that different people have different frequency sensitivities, so an image that looks correct for one person won't look "natural" for another (I've often wondered how effective going to a 5 or more band system would be for television); and that something that has its own narrow bands of reflected color that don't match the bands of incident light will look different than it would in "true" white light (of whatever color temperature).
With quantum dots effectively spreading the bandwidth of the light source into a wide spectrum light (which is not a new idea; I'm not sure why this is being considered a revolutionary new discovery, unless they were using novel techniques to produce the right mix of the right sizes), you could use any other low-power light source, not just LEDs. LEDs are convenient for some things because they can be used at very low power and last a long time. Where you need more light, you could use quantum dots with low-pressure sodium, for example, or conventional fluorescent bulbs except using quantum dots with a wide spectrum to do the fluorescing. The article also mentioned but didn't expand on using direct excitation with electricity to get quantum dots to give off light, which could be even more efficient.
http://www.llnl.gov/str/Lee.html
"With all these different colors, it's now possible to make light-emitting diodes (LEDs) from quantum dots," says Lee. "We've come up with a process so easy you can almost do it in your garage. We can put these dots in a polymer and make thin films that are 1,000- to 2,000-angstroms thick. This means we can create precisely tuned blue or green LEDs."
I think what they are trying to say is that the new light bulb will be something like this:
:-)
Single freqeuncy LED light (high effiency but ugly/annoying color) will be used to generate the initial light. This will hit a thin film of dots which will reradiate the light as white light that makes humans happy.
Saves costs as you only need one LED and multiple LEDs do not really match sunlight anyway.
Of course the article claims no heat is produced!
More likely UV, which many insect eyes are sensitive to, hence the fact that many flowers reflect UV very efficiently, and bug-zapping lamps use actinic light tubes.
I'm not going to change your sheets again, Mr. Hastings.
Combining narrow spectrum RGB sources can work to produce whatever perceived color you want, as in a display. It does not work for all reflective lighting needs, so a solid state broad spectrum source still fills a need.
"National Security is the chief cause of national insecurity." - Celine's First Law
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
Reinvent the wheel only at either a lower cost, greater effectiveness, or your own personal enrichment and satisfaction.
Since I was just at the store this week, a selection of compact fluorescents:
Panasonic GenIV, 14W 800 lumens (57.1)
- Very small bulb that can fit into any place that a regular bulb would fit (although it's not round)
Generic 26W, 1600 lumens, 10k hours (61.5 lumens/watt)
Generic 9W, 540 lumens, 10k hours (60 lumens/watt)
Prices on the CF bulbs have gotten a lot better over the years, most of them are down around $6-$7 for a single bulb compared to $10-$20 a few years back. The fact that you don't have to replace them as often is a big bonus.
Wolde you bothe eate your cake, and have your cake?
there about 45-55% effiency
Yep, I was wrong. The full text peer reviewed article is availabe: J. Am. Chem. Soc., ASAP Article 10.1021/ja055470d S0002-7863(05)05470-3
Web Release Date: October 18, 2005
Basically though: Magic-sized nanocrystals are so small that the electron wave function has significant overlap with the selenium surface sites.17,18 Therefore, any hole trapped on the surface would likely encounter the electron before nonradiatively relaxing to the ground state.
Quantum yield is currently only at 2-3% - I'd be curious to know what the theortical max for the quantum yield would be assuming better manufacturing of the dots. Also, these things do not last forever - in the paper they take them out to ten days of excitation, but I imagine it might be quite a challenge to extend the life of these.
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HomePower said the experiment was performed to compare lights suitable for task lighting, as opposed to room lighting; then they avoid using a CFL with a reflector that is suitable for task lighting. In other words, they lit up the entire room with the CFL, but concentrated the light output of the LED bulb only onto the measuring photocell.
Makes you wonder about the results of anything else in that magazine.....
Someone else pointed out to me that in the following issue of "Home Power" they printed a correction saying the test focused on task not area lighting so LEDs would be better because they concentrate light into a small spot. CFLs are still better for area lighting. Sorry about the confusion.
FalconShould there be a Law?