From: Jonathan Kirwan
Subject: Re: Make infrared goggles inexpensively (like $10!!!)
X-Newsreader: Forte Agent 1.92/32.572
NNTP-Posting-Date: Fri, 20 Sep 2002 01:22:10 GMT
Organization: AT&T Broadband
Date: Fri, 20 Sep 2002 01:22:10 GMT
I took a 5800 K blackbody radiation curve (Planck's Law for Sol) and
passed it through three Congo Blue filters and one Primary Red filter
(Leefilters was kind enough to send me data spaced on 1nm, ranging
from 250nm to 800nm -- sadly, I don't have information on those
filters longer than that.) This information was then further combined
with the x, y, and z filters from CIE and plotted. I also computed
the xbar and ybar values of (.6863,.2440). [Using 5555 K for Sol, you
get (.6903,.2458), in case that's useful.]
The combined filters yield two peaks: One at 444nm and one at 718nm.
The peak at 444nm is about 1/5th the height of the one at 718nm. So
it is clear that there is some sensation from the 443nm peak (about
from 410nm to 470nm.) The 718nm peak starts at about 655nm, by the
way. Intensity sensations are logarithmic, so keep that in mind.
The point here is that there is significant sensation in the shorter
wavelength part of the "traditional" visible band from 400-700nm,
looking through these four filters at reflected sunlight and that this
sensation is well within a magnitude of the longer, >655nm light.
What I'm curious about is whether the remaining light levels are low
enough that scotopic vision takes over. It depends on the lighting
levels before filtering, but if the rods dominate the response (given
time) then their response will be to the 430nm to 465nm passband.
Sounds like fun playing, though.