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homemade LED searchlight with visible beam

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hsieh

Tue Oct 11 2011, 04:28PM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

I am fascinated by those high power laser pointers that can show a visible beam.but I think it is too dangerous to use them in populated areas because it might be accidentally aimed at someone's eyes.I am thinking about building a LED searchlight that can show visible light beam because I think staring at high power LEDs for several seconds won't cause eye injury(I did so before when testing ten 1W white LED connected in serial).

Is my idea reasonable?If I want a 2cm diameter visible beam,how much power is needed?What can I use as reflector or lens to converge the light from the LED?

Shrad

Tue Oct 11 2011, 05:40PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

don't forget white leds are a spot of phosphor on an actually UV die, and it still leaks a vast part of UV

UV destroys blood cells and ages tissues, and you certainly don't want to do that to your retina ;)

Tetris

Tue Oct 11 2011, 08:28PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

O_O i cant stare at a single white LED. :D if you do so, use blue LEDs. They have very similar ouputs, one just has a cooler color.

Turkey9

Tue Oct 11 2011, 08:40PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

In order to get a visible beam in clean air, you will need a laser. What you're wanting to build is a laser pointer with a 2cm thick beam.

Rayleigh scattering is what makes a laser beam visible. In the case of a visible beam, this effect only occurs when there is a very high concentration of photons all traveling in the same direction.

My point here isn't that you can't build this device, it's that the searchlight will be far more dangerous than a simple laser pointer.

If you want a strong searchlight that can be seen in foggy or dusty conditions, then all you'll need is a parabolic lens with your LED at the focal point.

hsieh

Wed Oct 12 2011, 12:16AM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

I once own a LED flashlight that can sometimes produce a visible beam.And I want to build this after seeing this page

.How is work?

So, is it impractical trying to get a visible beam in clean air using non-laser light source?

haxor5354

Wed Oct 12 2011, 01:13AM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

hsieh wrote ...

I once own a LED flashlight that can sometimes produce a visible beam.And I want to build this after seeing this page

.How is work?

So, is it impractical trying to get a visible beam in clean air using non-laser light source?

by looking at the bright clouds in the dark sky, the photo was prabably taken by a camera set to long exposure time
so the beam looks brighter than it should to the naked eyes.

those lights are prabably high intensity discharge Xenon lamps or carbon arc lamps
I highly doubt those are LED lights

Patrick

Wed Oct 12 2011, 01:54AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Yes it was a long exposure pic. you cant tell from the sharpness of the static objects like the roof lines, compareed to the blurr of the cloud edges and stars which have relative or actual movement across the sky.

I agree that you need a laser, and the rayliegh effect to really do want your trying to pull off.

ill give you a hint:
The rayliegh effect is not constant or linear, it favors some colors over others. Use a laser of a favored color and youll at least have a starting point.

hsieh

Wed Oct 12 2011, 02:42AM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

I know the light in the photo is obviously not LED

I already tried a 100mW green laser ,but I worried that I might accidently aim at someone (or an aircraft) and cause injury.

So, are there any safer way to create visible beam in clean air?

Patrick

Wed Oct 12 2011, 05:44AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

hsieh wrote ...

I know the light in the photo is obviously not LED

I already tried a 100mW green laser ,but I worried that I might accidently aim at someone (or an aircraft) and cause injury.

So, are there any safer way to create visible beam in clean air?

I think moving up to Blue lasers might allow lower power to show a similar ly visible beam, but then again the human eye is most sensitive to green in terms of colors.

or just use green light and muzzle discipline.(so as not to cause airplane crashes)

Nik

Thu Oct 13 2011, 11:21PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

I disagree with those saying you cant have a visible beam in air from an LED spot light. I picked up a "3W" (the wattage is dubious) white LED flashlight because I wanted the LED. The reflector was almost perfectly parabolic and made a very tight, 4-5cm at 3M, beam that is visible at night or in the dark. With a better reflector I think it would be possible to have a visible beam of LED light.

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