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From: Louis Boyd
Subject: Re: Increasing IR LED Output
Date: Sun, 06 Oct 2002 09:09:07 -0700
Organization: Fairborn Observatory
NNTP-Posting-Date: Sun, 6 Oct 2002 16:09:08 +0000 (UTC)
X-Mailer: Mozilla 4.79 [en] (X11; U; Linux 2.4.18-3 i686)
Bob May wrote:
> In the end, it is usually better to just put more IR LEDs into the light
> source rather than finessing with modulationg the LEDs. Brute force does
> sometimes just work better.
Brute force is definitely effective. LED's start getting expensive for
output over about a watt. If LED's aren't adequate then a filtered
halogen incandescent bulb gives an economic infrared light source up to
100 watts or so. Putting optics on the light source to give a narrower
beam dramatically increases the range too, but with a reduction in field
width. Need more range? The military uses filtered xenon arc lamps in
the kilowatt range. Try a web search on "AN/VSS searchlight" made for
long range surveillance. I've used one of these with with a Sony
"XView" CCD camera and a 75 mm F/1.3 lens to give good qualtity RS-170
video at night up to a kilometer away. The lamp had to be offset 10
meters from the camera so as not to fog the view with nearfield
backscatter. There only a weak red glow visible from the lamp.
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