On 2007-06-05 16:38:07 -0700, Sam Goldwasser said:
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?
I have been unable to find a small enough flashlamp to fit in the
barrel, light bulbs are fragile (filament), and lasers - well I'd have
to replace ALL the targets with new optos (there are almost 100
targets) and that would take a lot of time!
White LEDs appear to be almost bright enough if using the lens systems
such as provided by L2Optics etc., these focus down to 9 degrees of
dispersion and this could be further collumated with a small lens -
perhaps producing enough light to trigger the cells reliably. Plus the
LEDs have a high output when used in pulse mode - which is what these
guns do - roughly 1msec light pulse.
I have found a smaller Xenon "U" flash tube that might fit in the gun
if I hollow out the bullet chamber - that is my next step. It is
simpler than using the LED etc, as the system is already set up to fire
photo flash tubes, 300VDC plus 4KV trigger pulse for the rifles.
The laser is ideal, but not going to set off the targets as they
currently are (CdS cells).
John :-#)#
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