LEC flashlights are becoming more popular. To get enough light to make them useful they arrange several LED’s in a small space. Why can’t they make one really big LED?
The light emission point between the two electrodes is fairly small, to begin with (picture). They would have to embed numerous electrode pairs in a common housing to achieve the “Big LED” result. That would then require a larger transparent housing with very specific refractive index (to prevent the housing material from absorbing and/or scattering the emitted light). My thinking is that this last item is the biggest problem with making the body of an LED very large.
That would be a more expensive LED and one that is less popular since it could only be used in certain specialized applications. Why not just use several “regular” size LEDs?
Actually, there are single LEDs that are rated up to 10W - equivalent to 20W incandescent. I have single-LED flashlights that are brighter than my 3-D cell Maglite. Look up Luxeon or Seoul Semiconductor Z-LED.
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What’s the wattage of light out?
I think they are about 5 or 6 inches in diameter , but some of the newest traffic signals are LED.
Declan
All the examples of that I have seen are LED arrays.
IIRC there was a big whoop a couple of years back that some company was finally able to make a 4-inch silicon carbide wafer… you just dip that in whatever LED goop it needs, and presto, giant blue LED. The reason they don’t do it is that those wafers are very pricey, and anyway a 4-inch LED would be far too intensely bright for most practical purposes. An array of small LED’s is quite sufficient and very cost-effective.
There’s one good reason for not making the LED all one big junction (even if you could). Although LEDs use a lot less energy than conventional bulbs (since they concentrate the output near one wavelength, where we can see it, rather than putting out a broad blackbody emission that’s mostly in the infrared wherre we can’t see it, but it generates heat), they still put out waste heat that has to be dissipated. (If it isn’t, the LED doesn’t work as well or, eventually, at all. And, as with more conventional bulbs, the lifetime decreases significantly if you run it too hot. THE MECHANISM IS DIFFERENT FOR leds, though0. Splitting the emitting surfaces up among a bunch ofd small LEDs is a better way to allow the heat to dissipate than concentrating it in one big LED (I actually have LEDs here on my desk with thermal pads to aid heat dissipation. They’re BRIGHT LEDs.)
This is all pretty much moot right now. I don’t think they can make large-area LEDs. But if they could, I still don’t think they would.
[nitpick] Light output is measured in lumens, not watts. Look at the lumens to compare the equivalent output from an incandescent bulb. [/nitpick]
(This is about the only fact I remember from my Lighting class in my days in architecture school.)
Generally, the light output isn’t rated in Watts, but rather Candela or Lumens. I’ve seen single-package LEDs rated up to 1200 Lumens, which is brighter than a 60W incandescent bulb: Powerful Little Light: LED With 1,000 Lumens
Note that Fluorescent light sources are still more energy-efficient than LEDs.
Infrared LEDs are rated by watts out (or something equivalent), because the number of lumens out is zero. You can’t see IR, and lumens measures visible light. It’s therefore the appropriate way to compare light output when you’re interested in lighting. But you can get output in energy as well Look for the spec sheets.
I did not know that! Consider ignorance fought once again.
Making any semiconductor very large is problematic. Making high power semiconductors large even more so.
The larger you make it, the more likely it is to contain a defect that ruins the whole thing. This lowers the yield, and increases the price, and is a real concern with microprocessors.
With high power devices you have a real problem with what is known as “current crowding”. One part of the device will, for various reasons, consume a little more current. This makes it get warmer, which makes it draw even more current. Wash, rinse, repeat. To avoid a runaway situation, the device must be operated at lower current density than a smaller device, so it is more efficient to use multiple smaller devices than one big one.
Combine this with the problems of getting rid of the heat, mentioned upthread, and you have a serious case of diminishing returns.
One more practical advantage is that if you have an array of small LED’s, and one burns out (rare, but it happens), the device is still mostly usable. If you have one big LED, the device is useless until it is replaced. Very nice feature for things like traffic signals and flashlights.
Indeed. Within 50 years, I predict there will be such demand that there be 8 to 10 such semiconductors in the world, and they will be housed in enclosures the size of very large buildings.
This is essentially the same question kids ask when you make cookies, isn’t it? - Why don’t we make one really big one?
What’s the defect density of a cookie?
Depends on the CCCI (Chocolate Chip Count per Inch).
Can someone verify that? It doesn’t seem right to me, but I wouldn’t know how to compute it.
What, you don’t trust me? 