LED Evolution Could Spell The End For Bulbs 482
An anonymous reader writes "USA Today is running a story discussing how LED lamps were unthinkable until the technology cleared a major hurdle just a dozen years ago. Since then, LEDs have evolved quickly and are being adapted for many uses, including pool illumination and reading lights, as evidenced at the Lightfair trade show here this week. More widespread use could lead to big energy savings and a minor revolution in the way we think about lighting."
Re:Bought some today! (Score:0, Informative)
Look at http://www.lumileds.com/
But the problem with LEDs today is that they are not more efficient than halogen bulbs.
A good halogen bulb give about 15-20 lumen per watt. A good LED doesn't give more than maybe 10 lumen.
Re:But it's warmer.. (Score:3, Informative)
However, as with all things, you can get flourescent tubes which have a really warming glow, and the halogen bulbs in my room have a much cleaner light than ordinary bulbs.
Additionally, they don't have mains flicker. When I went to the US the flicker from flourescent tubes drove me insane (in the UK they flicker at 50Hz, what is it in the states?).
Most white LEDs work using a different method (Score:5, Informative)
They haven't been used as sources of illumination because they, for a long time, could not produce white light -- only red, green and yellow. Nichia Chemical of Japan changed that in 1993 when it started producing blue LEDs, which combined with red and green produce white light, opening up a whole new field for the technology.
This is certainly one way to produce a white LED but it is not the common method today. Most white LEDs use a phosphor to convert a blue or ultraviolet LED into a white one. A quick google found the following page that talks about this in more detail:
http://www.marktechopto.com/engineering/white.cfm [marktechopto.com]
I would speculate that for normal home lighting using a phosphor will give better results as:
Drag Racing (Score:4, Informative)
Re:But it's warmer.. (Score:2, Informative)
Now, technically our eyes only have receptors for red, green, and blue. So, what you would see would look mostly the same as under true white lite. However, the way light reflects off of surfaces can be more complex than that. Imagine a surface which only reflects light in the yellow range (that is, it does not simply reflect red and green, but in fact reflects only the yellow wavelength of light). This surface might appear yellow under natural light, but would be black under this LED light!
In general, you won't see such extreme differences. But, there will be subtle differences between colors viewed under these white LEDs vs. an old-fashion light bulb. Will you care? Maybe, maybe not. Fluorescent light has the same problem, and personally it never bothered me. But, yes, I can certainly imagine there being "illumiphiles" who are bothered by it.
Oh yeah... and if you're one of those mutants with a fourth color receptor, you'll hate these lights.
Re:I like the color-mixing aspect.. (Score:4, Informative)
They have excellent focus and can illuminate pretty darned well, projecting the light to a good distance as well as a very effecient battery usage.
I do not even remember the last time I used a lightbulb based headlamp.
So, to answer your question - current LEDs can probably do that already.
Re:Bought some today! (Score:5, Informative)
Regarding efficiency, I refer once more to Wikipedia: "In 2002, 5-watt LEDs were available with efficiencies of 18-22 lumens per watt. [...] In September 2003 a new type of blue LED was demonstrated by the company Cree, Inc. to have 35% efficiency at 20 mA. This produced a commercially packaged white light having 65 lumens per watt at 20 mA, [...]".
Re:Need to fit normal lamp-sockets. (Score:5, Informative)
They've been out for some time.
http://store.sundancesolar.com/ledlibu12acl.htm
http://www.smarthomepro.com/97314.html
http://
The technique is simple. Use a rectifier to convert AC to DC, and use enough LEDs in series and glue them all together. Sure if one LED burns out you loose a whole series, but don't expect that for a few years.
Whether you'd actually want to own one is a different story.
Re:But it's warmer.. (Score:2, Informative)
Re:But it's warmer.. (Score:5, Informative)
Yes, I am. You might be too ...
Most people have another type of receptor, called a rod, which is not colour sensitive, unlike the three kinds of cones which are colour sensitive. However, my rods have a much wide spectral response than the normally accepted colour range of white light. I have known for a long time that light without significant ultraviolet content makes it hard for me to accurately resolve edges. I find technical drawing very difficult by incandescent light. Others may be the same too.
Remember 10% of men lack one kind of cone, and are partly colour blind. A lot more lack fashion sense, but you can't blame that on LEDs
Comment removed (Score:3, Informative)
Re:But it's warmer.. (Score:5, Informative)
So, pretty much, newer better lamps shouldn't flicker perceptibly. I know my CFL's don't, and ever since we got the ballasts replaced the tubes at work don't either. But I guess YMMV.
Re:But it's warmer.. (Score:5, Informative)
Did you actually did this experiment? Modern white LEDs have a single light emitting junction that mostly emitts light in the blue part of the spectrum. This junction is then covered with a phosphor-like coating that converts a narrow band of wavelengths to a broad band that you see as white light. This means that white LEDs have a continuous spectrum, much like the light bulbs.
Re:LEDs are definitely becoming more powerful (Score:2, Informative)
You can also notice this effect when someone creates an image with red and blue (ie, some badly done websites).
Re:But it's warmer.. (Score:5, Informative)
It isn't science-fiction.
To simply, some women are blessed with color receptors that allow them to see a color between the green and red wavelengths. Their idea of the world and it's colors is much more vivid than most people's.
It's almost certain that all tetrachromats would have to be women.
Re:But it's warmer.. (Score:5, Informative)
Re:But it's warmer.. (Score:5, Informative)
bah
lone
ey
All modern white LEDs are single indium gallium emitters in the blue to uv range that are coated with a phosphor somewhat like that in a flourescent lamp. The energy from the blue led excites the phosphor into producing a multitude of wavelengths which we perceive as "white." Generally, the thicker the phosporus coating, the warmer the light (lower color temperature). The output is definitely a lot richer than three simple RGB wavelengths.
Re:Slightly off-topic, but... (Score:3, Informative)
We are VERY early in the development of using LEDs for illumination, wait a couple years and see what happens.
You jest, however (Score:5, Informative)
The way that it is talked about, is called colour temperature, and it is spoken of in kelvins. The idea is if you heat a black body radiator to that temperature, that's the kind of white you get. The lower the temperature, the more red in it, the higher the temperature, the more blue.
On most monitors that aren't connected via DVI, you can see colour temperature changes for yourself. In its configuration there should be a colour temperature option, generally with three presets: 5000k, 6500k and 9300k. PLay with them and notice the change. You'll probably find that changing from the one you are used to looks "wrong", either too red or too blue depending on. That's an illusion, however. If you go away for awhile and come back, or just ignore it and keep working, you'll find your eyes adjust and consider that to be white.
With bulbs, it gets more complex because it's not just a function of the temperature of the white, but of it's spectral composition. Most incandesant bulbs have a spectrum that is low on the high frequencies (near violet) and high on the low frequencies (near red). Other lights, like many floursecants, have an uneven spectrum, with peaks all over.
Now ideally what you are shooting for usually is light as close to sunlight as you can get. That's what humans would generally think of as "normal" or "correct" lighting. Easier said than done, of course.
So I don't know what the spectrum for any of the varities of white LEDs looks like, but it is very possible, even likely, that they are different than an incandescant bulb. It may be that they have a generally higher temperature and thus really are cooler, colourwise.
Re:Did you read the article? (Score:3, Informative)
Even perfect RGB cannot cover all colours (Score:5, Informative)
To summarise; consider that the red, green and blue receptors are sensitive to a *range* of colours; the sensitivity curve for each receptor is roughly bell-shaped, peaking on red, green or blue light. There is also some overlap between the red and green sensitivity curves, and between green and blue (not red and blue IIRC).
This is of course essential. Sensitivity narrowly focused on R, G or B would leave us unable to see intermediate colours (e.g. yellow!).
Reasonable overlap is necessary, or
(A) there would be certain intermediate frequencies that were not covered sufficiently by either receptor (e.g. certain shades of yellow in the valley between the red and green curves would be very hard to see), and
(B) Colours would be quantised into 'red group', 'green group', or 'blue group' (think about it...)
Because of the (necessary) sensitivity-curve overlap, the green receptor is slightly sensitive to red light, and so on. Where is this leading, you ask?
True cyan has a frequency between blue and green. This is within the sensitivity range of both blue and green receptors; the brain can use the 'ratio' to figure out that it's looking at cyan. But true cyan is (to all intents and purposes) outside the red receptors' range, so the red receptor is not stimulated.
Simulated cyan is made up of green and blue light. This stimulates the green and blue receptors in the same ratio as true cyan would, so in theory looks just like the real thing. However, the red receptor is also slightly sensitive to green light; thus, unlike with real cyan, the RGB-mixed version also stimulates the red receptor.
This is (supposedly) what makes certain RGB-generated colours less convincing (hence the linked story above).
This isn't even counting the fact that our colour receptors aren't exactly R, G and B, and therefore to simulate certain colours using RGB is impossible, as it requires one or more components to be negative. (If the receptors were exactly R, G and B, that would not be the case).
Already used in stoplights... (Score:5, Informative)
Re:Is this true? (Score:2, Informative)
As for half life, the 50,000 mark mentioned by the author IS the half-life. Most diodes are listed under 100,000 hour life mark, with 50,000 hours without any failures. Lumileds guarantees 70% lumen output by the 50,000 mark, but that is definetely not an industry standard. While Lumileds certainly managed to grab a nice portion of the market, their 'design' is questionable. The y keep pushing the lumens (most recently 190 lumen) by cranking the power to the diode (190 lumen at 1.4amps).
Recently, Nichia and other big LED manufacturers put out some very nice 0.5Watt diodes that take a fraction of Lumileds power and eliminate one of the biggest problems associated with Lumileds LED's.. HEAT! From a point of thermal design, Lumileds LED's is a pain to say the least. But at least others are moving in the right direction, instead of producing single LED light source, arrays of LED's seem to be the way for the future.
Re:But it's warmer.. (Score:3, Informative)
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=P
Re:But it's warmer.. (Score:1, Informative)
Re:But it's warmer.. (Score:3, Informative)
Hmm, don't think so. (Score:5, Informative)
I doubt it, at least not the kind of person the grandparent is referring to. If you are you should be calling a research lab and asking for bids to be a guinea pig. Tetrachromats are extremely rare.
This hypothesis sounds more likely (from http://www.physics.utoledo.edu/~lsa/_color/18_reti na.htm [utoledo.edu]
Rods and all three cone types readily absorb ultraviolet radiation, photons of which are energetic enough to damage these delicate cells. The reason we cannot see in the UV is because the eye lens is opaque in that wavelength range. In addition, the cells in a region called the macula surounding and including the fovea contain a yellow pigment that further prevents short wave radiation from reaching the photo-receptors. Some people with less of this yellow pigment and those who have had their lenses replaced with plastic inserts can see further into the UV than normal people can.
Re:Bought some today! (Score:1, Informative)
http://www.lumileds.com/pdfs/DS45.PDF [lumileds.com]
See Figure 1a, Page 9.
You'll see that a "Typical" Green Luxeon 3 will output 50% of its peak wavelength's power from ~510 to ~550nm. 20% from 490-560nm. Hardly monochromatic.
If you happen to have a loose LED, power it up in a dark room, take any old CD, and using the diffraction grating on the CD itself look at the spectrum of the LED.
But you do have a point, some objects with colors that reflect mainly in these "holes" in the spectrum may look off.
But if you just want a good "Color Rendering Index (CRI)", use a normal white LED that uses a deep blue die with a phosphor painted on. See Figure 1b on the above link.
But if you want a color washer with a good CRI, you're going to end up using about 10 different wavelegth LEDs.
Re:But it's warmer.. (Score:5, Informative)
Light bulbs, incandescent or fluorescent, running off of house current "flash" 120 times per second.
Re:But it's warmer.. (Score:5, Informative)
When I went to the US the flicker from flourescent tubes drove me insane (in the UK they flicker at 50Hz, what is it in the states?).
60Hz in the US, so for single tube installations you should see less flicker. However, in the UK, the Health and Safety regulations for offices require that multi-tube installations have the tubes fed from different phases of the supply. So a typical office setup with three tubes, one on each phase, gives you almost no noticable flicker.
Re:But it's warmer.. (Score:3, Informative)
Re:You jest, however (Score:2, Informative)
The color temperature of sunlight is approximately 5000-6000K which is actually more yellow-ish than actual white.
I'm sure if you're not used to distingushing between various hues around white, that the brain can be fooled into seeing what it thinks of as 'white', but it's not entirely a relative thing, since noone could be fooled into thinking say... 1000K or 15000K was white.
Re:But it's warmer.. (Score:3, Informative)
Yeah, but incandescent don't have as much as an impulse to the flash. This is mostly due to the fact that they produce light as side-effect of their heat, and the wire doesn't cool down anywhere near as quickly as the next peak in the current. As a result, incandescent bulbs have a much smaller delta between the 'bright' and 'dark' parts of the cycle. Turn the power off on an incandescent bulb, and it has a perceptible dimming after the power is gone. Flourescent bulbs just go dark instantly.
Actually, they do, and no, they don't. (Score:2, Informative)
A google search will explain.
Re:But it's warmer.. (Score:3, Informative)
One cause of tinnitus (ringing in the ears), is when a hair cell (sensor) stops sending its signal . That's also why the sudden cessation of a background noise will get your attention.
Optically, think of it as your white balance getting messed up. Another example of this is divers who take underwater photos (without flash to compensate for the water filter the red out of the sunlight), then wonder why the developed picture is much more blue than they remember everything.