Two general LED questions.

Hi, this is my first post here. I have done some digging and have found no answers to these questions, but I apologize if the solutions are obvious or have been discussed before.

1) Why is nobody developing very large LEDs (70mm+) for things like automotive headlights and house lighting? It seems like everyone is concentrating on LED arrays instead of increasing the size of the "bulb" itself. I imagine that heat is a big concern, but it seems like larger units could be more easily focused with reflectors like traditional 9004 (etc) vehicle headlights while still retaining a big advantage in efficiency and wavelength considerations.

2) Are there any Internet resources that explain in detail how LEDs are constructed?

Ill give this one a try. LED size is based on the size of the dice, or the crystal. this is very small. A 1 watt is about 1mm x 1mm. The larger you make them there is problems with heat dissipation, and just the process of growing them itself...

As far as a site explainig how they are grown/constructed..
I don't have anything.

Jeff

ELJ

The answer to your second question, will also answer your first. What searches have you made on the topic so far? If you draw a zero, I'll point you to a few. You just have to use that search function.

GregR

Here is a general overview.

And a "homemade" L.E.D.

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ELJ said:
1) Why is nobody developing very large LEDs (70mm+) for things like automotive headlights and house lighting? ...it seems like larger units could be more easily focused with reflectors like traditional 9004 (etc) vehicle headlights while still retaining a big advantage in efficiency and wavelength considerations.

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I believe (though I'm not a lighting designer) that in general, smaller light sources are actually more easily focused.

Simple lamp reflectors are variations on the parabola, with a light source at the focus point. A real lamp filament isn't a true point source, of course, which can mess up the light projection. But with a linear filament, for example, you can at least align the filament with the axis of the reflector, so the variation from a point source is at least one-dimensional, and in a relatively easily dealt-with dimension. LED emitters are planar in shape, and a large one would probably be much more difficult to focus. Consider the dearth of florescent headlight designs; florescents are far more efficient than incandescents, but their low intensity (and thus the large area needed to emit suitable amounts of light) would make them too hard to focus.

I also believe you'll find that the efficiency and wavelength advantages of LEDs may have been... exaggerated.

LEDs are rugged and long-lasting, and they don't lose efficiency when run at reduced power, the way incandescents do. That makes them great for flashlights, which need to survive a few hard knocks and deal with a variable power supply as their batteries fade. But they're only about as efficient as halogen bulbs for producing white light.

Colored light is a different story. Monochromatic LEDs are usually a lot more efficient than an incandescent bulb with a power-sapping colored filter. So you do see LEDs used in traffic lights, where they can shave big bucks from a municipal electric bill, and in taillights and turn-signals, where their fast startup time can actually be a safety advantage.

I'm not sure exactly what you mean by the wavelength advantages, but a halogen bulb is about as good as it gets in terms of emitting the whole visible spectrum. White LEDs, like florescent bulbs, sodium street lamps, and HID headlights, only emit a few colors, selected to fool your eye into thinking you're seeing white light. It's not always completely successful. Vibrant red colors in particular look washed-out and dull under "white" LED light, which is really only narrow spike of blue and a few colors near yellow, with very little actual red.

All you ever wanted to know about semiconductors:
http://britneyspears.ac/lasers.htm

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Lagged2Death said:
I believe (though I'm not a lighting designer) that in general, smaller light sources are actually more easily focused. ...


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My understanding is that it is easier to do the calculations the closer the source is to a theoretical point source. With some sources their size blocks the efficient use of simple reflectors. This is why smaller diameter florescent are preferred over their larger cousins.

George