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LED Evolution Could Spell The End For Bulbs
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."
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
I would speculate that for normal home lighting using a phosphor will give better results as:
The drag racing industry has moved from incadecant to LED lights for the starting "Christmas Tree"
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Actually, rock climbers & spelunkers who do lots of caving have been using LED based headlamps for a while now.
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.
I thought white LEDs are usually blue LEDs, which are coated with a scintillator, which converts parts of the blue light to yellow. Wikipedia seems to support my impression.
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, [...]".
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Sure you buy new lamps every once in a while, but a real breakthrough will come when you can get LED 'bulbs' that fit in a normal 220/110V socket on a normal lamp.
l w ww.ccrane.com/120-volt-led-light-bulb.aspx
They've been out for some time.
http://store.sundancesolar.com/ledlibu12acl.htm
http://www.smarthomepro.com/97314.html
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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.
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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
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I'm in the US, I perceive flicker on 70hz and below refresh rate monitors, and on some old fluorescent lighting (but I've gotten used to it and can deal with it). But the thing is, a properly ballasted fluorescent lamp doesn't flicker at 50 or 60 hz. It flickers at 100 or 120 -- the ballast doubles the frequency from the mains frequency. Which is faster than most people perceive. However, solid state ballasts go WAY faster than that ... Wikipedia's entry on ballasts is pretty 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.
In fact, there is a major difference, even in theory. A white LED light is produced by combining red, green, and blue LEDs. If you were to take this white light and run it through a prism, you would not see it defract into a rainbow. Instead, you'd see a red beam, a green beam, and a blue beam.
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.
Tetrachromats
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.
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I'm not the one you replied to, but I did look up the spectrum -- it's shown here. It's definitely more spread out than I would have guessed, but it doesn't look like an incandescent,
In fact, there is a major difference, even in theory. A white LED light is produced by combining red, green, and blue LEDs.
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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.
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Warm and cool are really terms used to describe white light. When you talk about white the question becomes what is it? A blend of all the colours is an elementary explination, but the fact is they aren't all present in equal levels, from any source.
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.
There are also more subtle issues at work with the 'R/G/B mixing' approach to colour generation. You can read more about them here.
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).
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I think all the new stoplights in town are LED stoplights. Most of the brakelights on trucks around town are too. Did this story fall through a time-rift from seven years ago?
Correct, white LED is just a phosphor covered blue led. The patent is owned by Nichia and you can view the specifications here:
T O1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm &r=1&f=G&l=50&s1=5,998,925.WKU.&OS=PN/5,998,925&RS =PN/5,998,925
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=P
That is because your mind plays tricks with you. In this case, the image you see outside contained more red than other colors. Your mind will compensate for this by adding the opposite color (on the color wheel) to the image. For red, the opposite color is green. Here's a link that contains much information about this.
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
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.
Light bulbs, incandescent or fluorescent, running off of house current "flash" 120 times per second.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
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.
What would Lemmy do?