1. ## How Large Can LED's Be Made?

I was just wondering....would it be possible (if money were no object) to produce an LED say the size of a fifty-five gallon drum lid or larger? So large that it would take something like 110 volts AC to run it? I have no idea what the need for such a large LED would be, maybe to position it on a satellite in orbit to turn night into day in a small region? I'm just making this stuff up here so no need to call me stupid or crazy for asking something so weird. As the young folks are fond of saying nowdays, "I'm just askin."

2. ## Re: How Large Can LED's Be Made?

Anything is possible, but the size limitations for growing a single crystal wafer substrate would be about 30 cm. So realistically you're not gonna be able to make things much bigger. Plus current distribution and heat could be a big problem.

3. ## Re: How Large Can LED's Be Made?

There's nothing at all stopping you making an array of emitters that large, but I'd guess there'd be a lot of technical difficulties with making a single chip emitter. For one, looks like the biggest wafer substrates they are using at the moment are about 6inches diameter. And I'm guessing (don't really know the technicalities) that you need conductor wires to every x amount of area, which would get to be a right royal mess.
Simply put, no benefit in a single large emitter over a multitude of small emitters, and lots of disadvantages.

I very much doubt anything man-made orbiting in space could be made bright enough to illuminate the ground. I won't say "ever" though.

4. ## Re: How Large Can LED's Be Made?

On a power level as well, you wouldn't be running 110 AC through it. The larger the die gets, the more current you need to send through it, not voltage. So while you could technically have a 4 or 6" wafer as a single die you'd end up requiring a ridiculous amount of current. A 4" dia wafer is 12.56 in^2 or 7740 mm^2. Assuming full power is 1A per 1 mm^2, you're pumping 7740 A through it. Total power is over 25 kW. The wafer isn't 100% efficient, even dissipating 10% of that over a 4" dia area would be insane, not to mention the resistive losses from any and all connecting wires carrying that amount of current.

Of course, you could run it at a lower power level, but then it becomes increasingly pointless to have a die that big, and the thermal and power issues will still be present to some extent.

Putting it in space would be even worse, there'd be no air to dissipate heat (as if passive cooling would be able to handle that amount in the first place). Heat dissipation of electronics in space is actually a fairly large concern.

5. ## Re: How Large Can LED's Be Made?

I did a google search for the wafers that cree uses in their newest leds, the silicon carbide wafers they use are 4 inches in diameter, so that's probably the practical limit right now with that wafer material.

http://spectrum.ieee.org/semiconduct...ster-tougher/0

6. ## Re: How Large Can LED's Be Made?

Originally Posted by ConfederateScott
position it on a satellite in orbit to turn night into day in a small region?
No point in creating an emitter that big when you're in an ideal spot to reflect sunlight; a satellite with a giant array of mirrors arranged in an "Archimedes Death Ray" configuration could probably light a shopping mall-sized area..

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