# LED to laser beam?

I have just started the optics section of my physics class and I was amazed to learn that one can use a simple magnifying glass to form a beam from an LED.  Could this be used with a high power LED such as a 100 watt one, and then a beam expander (backwards to compress it) to form a laser beam of sorts.  Obviously it wouldn't have a common frequency, but could one theoretically make a very high power, burning beam with this quite easily. I know from experience that holding your finger in front of a mere 10w led can get quite hot, so couldn't using a 100 watt led yield some awesome ant killing hotdog frying results?  If not, how many beam combiners would you need to make it work

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mpilchfamily2 years ago

Shinning the light from an LED through a beam expander from the opposite end will not condense the light into a beam. Investigate how a laser is made. A magnifying glass will certainly focus the light from an LED to a single point but it's a focused point of light not a beam. It scatters past it's focal point. But that focused point can do some burning much light sunlight through a magnifying glass. Not sure you'll get ant popping result from a 100W LED. You'd need a good reflector to help focus all the light from the LED towards the magnifying glass. Then you'll need to find the optimal focal point of the reflector to line up with the glass and then find the optimal focal point from the glass.

seedorfj (author)  mpilchfamily2 years ago

Shining the light through a magnifying glass will from it to a beam, which can then be condensed. I've done that much, it works, its how stage spotlights work. This beam can then be condensed and will result in a relatively nice small beam of white light which could be between 5 and 1 mm if not smaller. Then, it could be focused, even laser cutters must focus the beam to cut and make it as small as possible.

rickharris2 years ago

LED does not = LASER for several reasons discussed in other posts.

and 10 watts is 10 watts no matter what you do, yes you can focus the beam but it will simply look brighter. An LED is quite efficient and produces comparatively little heat energy.

seedorfj (author)  rickharris2 years ago

The only difference between a good beam from an LED and a beam from a laser is that the light isn't coherent (same wavelength). You easily focus all of the light from an led to a very small point. If LEDs are so efficient then maybe they are going to produce more light energy than a normal laser, of course the interference of light will likely be problematic.

-max-2 years ago

You can get OK focus, if the LED die is small, and the reflector (concave mirror) is large, or the magnifying glass is large. Try sticking a flashlight in front of a magnifying glass, or a 40W light bulb, you will notice instead of focusing the light to a point when the wall is far away, it creates a inverted projected image. There is lots of great info online about the subject, and how it can be used to make camera's and such.

Do this with a standard 100W LED, you will just get like 25 square dots projected onto everything (same shape as the LED emitter itself.)

The short answer is sort of. You can get more focus, but not a laser-tight focus. Unless the LED has infinitely small radiation area.

iceng2 years ago

You might like to see what a big Fresnel lens and an LED can do !

https://www.instructables.com/id/INCREASE-LIGHT-by-...

2 years ago

Oh, and you might like how to make the LED driver.

https://www.instructables.com/id/POCKET-THIEF/

Downunder35m2 years ago

You might like this crazy German for his HID "flashlight":

As you can see it a lot of heat but no properties of a real laser beam.

Downunder35m2 years ago

Spend some more time in your physics class and you will understand why it is not working.

I'll try to make it short...
A laser is a coherent lightsource with quite special properties.
A normal LED is just a source of light.

You might be able to get some sort of focus but never a truely parallel beam like from a well focussed laser.
Simply because your light source has a much larger emitting area, resulting is possible extrem small focus points but quite some problems creating a parallel beam of light.

Check the size of the actual light emitting panel on a 100W LED and you will agree it is quite hard to create a focussed beam of less than 1mm in diameter from it.

Same story for HID lamps by the way, although they offer a very small, point like light source.
You can focus them with extra reflectors to burn through wood with no problems but only at a single fixed focus point as the properties of a laser are simply not existing.
Makes a damn bright burning toy wasting a lot of energy but not a laser.