back to infra-red (IR)

IR lights:




Infra-red is basically where heat meets light. All "radiated heat" is actually infrared light, at various
wavelengths outside the human eye's ability to detect. They're in the 850-940mn range, where 850 is still
slightly visible and by 940 it can't be seen anymore.

Many years ago I had bought a basic IR monocular, and it came with an onboard light, but it sapped the battery
and this unit used a pair of non-rechargeable, hard to find batteries, and wasn't very bright, so I tried to
find or build my own light. I had IR LEDs but those were way too dim.

A friend was getting into the hobby of glasswork, and suggested I check out the store she bought her glass at.
We stopped by and I brought along my IR monocular and an IR LED with power supply, just to test how the glass
sheets passed or blocked light. Many blocked IR even if they looked transparent.

I got to looking through the "junk box" of broken or undersize remnant glass bits, and found a 2x2ft piece with
the corner broke off, that LOOKED completely black, which seemed odd for glass, because why would you want to
use glass that you couldn't see through? So as I was testing the other semi-transparent colored sheets, I
stopped paying much attention to what I was grabbing as I looked through the monocular at the IR light, with
a glass sheet between them. I came to one that didn't really dim the LED at all, and when I looked up at the
sheet I was stunned to see it was completely black. I had found the holy grail, it could be placed in front
of a regular light, completely block all visible light, and yet work as a flashlight (or flood light) for the
IR monocular. Unfortunately that was the only sheet like it in the box, but I got a good deal on it and she
was able to cut me a few round discs out of it, one for my small 2xAA flashlight, one for my larger mag-light,
and a big one for my million-candlepower spotlight.

It worked as expected for the flashlights, you could just barely see a very faintly red glow with the naked eye,
but it was a perfectly working flashlight for the monocular.

The big one was the real surprise. I turned on the light and thought I hadn't plugged it into power. No, it
has that faint red glow about it... but why are my eyes itching and starting to water? and my face is getting
HOT. Oh... infra-red light, of course. My eyes can't "see" it, but they certainly know they're getting
absolutely blasted by it.

Unfortunately the glass gets pretty hot when used, especially with the big million candle 12v lamp. But it's
turning all that visible light into heat when blocking it, so that's understandable.

Some years later I spotted an actual military grade disc for use as an IR filter on a big spotlight and bought
that. It was made of a much more substantial glass and would probably survive for longer in use. It worked
just about the same as the one I made years earlier.

Nowadays LEDs are all the rage, and high-powered IR modules are available for battery-powered flashlights.
Or you can go the macgyver route with a platter of 5mm LEDs, common with outdoor security cameras.



high-power IR flashlight


IR flashlight search (at Amazon)



last updated 08/30/2026 at 19:56:42 by make_www_index.command version 2026.07.10.A