Any chance to collimate LED light ?

[Externet]

Hi.
Can a single or a bunch of LEDs aimed to some proper lens produce its light to be collimated ? Ideal/satisfactory range is a red or green 100mm diametre dot at a 1Km target. I do not know if their emitted light is good coherent monochromatic and power/lumen requiered.
How would such lens be ? -A laser can do it but not to be considered here-

 

[biff44]

yes you can collimate LED lights into a "beam" using lenses and positioning.
you will be difraction limited, of course, in how small a spot size can be achieved.

there is not way to "coherently" combine LEDs as their colors and phases are not controlled, to it would be like trying to get two sources at different frequencies to be "in-phase" -- i.e. its not going to happen.

there are some inexpensive plastic "light pipes" that i bet can be used to incoherently power combine multiple LEDs

 

[BradtheRad]

I wanted to flash an led and pick up its light from across the room.
Start with a narrow beam led. Lens of clear plastic. Yellow or orange. More lumens is better.

I hoped it would work simply to hold one inexpensive lens in front of an led and obtain a small dot at the end of a hall. However the dot is never smaller than a dinner plate.

Evidently this project is difficult otherwise solutions should be easier to locate. A system of 2 lenses might work. Something like a telescope in reverse. You want parallel light rays coming from the large lens or mirror.

Collimation is done for lighting in microscopy, schlieren systems.

If you shoot a camera flash in the eye tube of a telescope, a narrow beam appears momentarily coming out the large end.

Youtube has various enthusiasts. 'Light cannon' projects. Reviews of adjustable-focus spotlights. Blindingly bright. It should be possible to achieve your spec distance up to 1 km.

A type of lens designed for led's is called a tulip lens. Youtube link:

 

[mtwieg]

I played around with collimating lenses and LEDs quite a bit recently, it's surprisingly hard to get FWHM below 10 degrees. 100mm spot diameter at 1km distance is far beyond what collimating lenses are capable of, even with multiple lenses. Only a true laser has a chance of making such a narrow beam.