LED Light Array: Why Several Small Ones vs One Large?

[FulhamFan3]

There's a lot of products with LED's these days. However I was wondering why a light made with LED's is done with an array on LEDs instead one large one. Can we not make a large one? Is it possible to make a large LED but it's actually more efficient to have several smaller ones?

Any insight would be appreciated.

 

[berkeman]

Probably the cost of that large a piece of silicon. It's probably more cost effective to get as much light as you can out of as small a piece of silicon as you can (more die per wafer), and use cheap plastic to distribute that light out.

 

[turbo]

And don't forget redundancy. If you have a stop light made with an array of 100 LEDs and one of them fails, is that going to change the way people behave when the light comes on? At least it's not a single bulb that can burn out and cause confusion (and fender-benders).

 

[FulhamFan3]

And don't forget redundancy. If you have a stop light made with an array of 100 LEDs and one of them fails, is that going to change the way people behave when the light comes on? At least it's not a single bulb that can burn out and cause confusion (and fender-benders).

For a traffic light I understand. I was speaking more in terms of illumination like flashlights.

 

[Danger]

The same could apply there as well. In the Canada AM technical section this morning, it was pointed out that the various LED household lamps are disposable. They cost anywhere from $50 to $200, but are supposed to last up to 20 years. After 10 years or so, they start paying for themselves with reduced electrical usage (5 watts vs. 40 for the same amount of light). Everything is hard-wired, so you can't replace the LED's. I can see somebody being mightily ticked off if one conked out due to a faulty chip if it was one big piece. (I'd be ticked off if even one of dozens went out, for aesthetic reasons, but that's beside the point.)
I rather suspect, though, that Berkeman's answer is the applicable one.

 

[Manchot]

Probably the cost of that large a piece of silicon. It's probably more cost effective to get as much light as you can out of as small a piece of silicon as you can (more die per wafer), and use cheap plastic to distribute that light out.

If the substrate was silicon, then we might see giant LEDs. Silicon's cheap. Unfortunately, silicon is an indirect-gap material, and most LEDs are made from more exotic direct-gap materials, like Gallium Arsenide and Gallium Nitride. These materials are several times the price of silicon. (Although, I have read that one group is working on making a blue silicon LED, though I have no idea how that would work.)

 

[gedion4000]

the material isn't really the cause for the lack of large leds.

large leds have only recently become possible. most led's no matter how large they are only have an element that emits the light about 1mm square. it stands to reason that the larger the emitter is, the more light it gives off. its true, however, the larger it is, the greater its ability to ABSORB light is, it reaches a point where the light level begins to drop off and becomes less efficient.
think of it as being a black car sitting in a sunny parking lot. the black paint soaks up a lot of the suns heat, it absorbs it, but at the same time, its freakin hot if you touch it because it also radiates the heat back out...it does both.

just recently a company called luminus developed a film that sort of acts like a one way gate for the light. that's the best way i can explain it. some of there led's emitters get up to 12mm square. thay are used in a lot of projectors, tvs, lighting fixtures etc. 8k lumens from a single led is impressive.

hope this answers the question.