John Robertson writes:

Hi Folks,

I'm fixing up an old light beam activated rifle gallery and want to
convert some IR Laser diode Colt-45 style pistols to a white light LED
or possibly tiny photo-flash tube.

The targets all work on visible light and use CDS cells (are these
being banned?) as the sensors.

What I have been toying with is using a 60,000LCD(?) white LED as the
light source but I'm having trouble focusing the light so that it is no
larger than about 6 - 8 inches in diameter at twenty feet. I'm not an
expert on using lenses but the flash tube version of these use a metal
shield with a small hole - I suspect to act as a point source of light
- then the lens is about six inches away. This produces a nice bright
flash at the target distance.

My problem is I can't FIT a flash tube in the barrel of the pistol! Ths
smallest flash tubes I can find are used in disposible cameras but do
not work well as there is not much light coming out the ends - the
elements are in the way. Can't bend them into a "U" shape as they would
simply collapse once heated enough to soften the glass.

The smallest u-shaped strobe tubes I can find are just over 1/2 inch
wide and the barrel is only 1/2 in internal diameter - won't fit!

So, I'm thinking I need to find out a couple of things - first; can a
high intensity LED but over driven, repeatedly, on a very short duty
cycle? And second; how the heck do you focus the bugger to something
resembling a small - but intense - circle of light at twenty feet (6
meters)?

Keep in mind that laser diodes have the nice ability to be collimated
quite well with a small lens.

And flashlamps have the nice ability to produce a high peak light output.

LEDs have neither.

Why do you want to change it?

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