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[DPRG] Spectral Content

Subject: [DPRG] Spectral Content
From: Ted Larson ted at larsonland.com
Date: Wed Jul 30 11:46:26 CDT 2008

Most IR remotes are in this 800-900nm area for this and many other reasons.
So I continue to disagree with John on the idea that noise, and spectral
content is equally distributed no matter what wavelength you use.

One other thing I was just doing some reading about was the issue with eye
safety and near-infrared light 700-1400nm light.  It doesn't trigger a blink
reflex in the eye the same way visible light does, so it is possible to
damage your eye with a sufficiently powerful laser diode setup.  I found
that info on this website....it is a good one for everything laser.

http://www.rp-photonics.com/encyclopedia.html

Also, the Wikipedia LIDAR entry, talks about using 1550nm light, because it
is eye safe at higher power levels, and is not visible in typical IR
sensitive devices like night vision goggles....so obviously the military
likes it.  But, I guess finding detectors that work at that wavelength is a
challenge.

http://en.wikipedia.org/wiki/LIDAR

Thanks,

-Ted




-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On Behalf
Of Ed Paradis
Sent: Sunday, July 27, 2008 3:50 PM
To: Kenneth Maxon
Cc: dprglist at dprg.org
Subject: [DPRG] Spectral Content

That is a great graph. It looks like there is a big gap around 900nm
and another around 1100-1200nm.  I wonder if the 'IR' that most
remotes use is around that range.  It would be wise, as at that point
your signal to noise ratio would be much better.

Ed

On Sun, Jul 27, 2008 at 3:23 PM, Kenneth Maxon <kmaxon at qwest.net> wrote:
>
>
> Good observation.  In the IR range there is still plenty of spectral
> content, although from a energy delivered as natural light source it is
> beginning to fall off.  On the other hand, in the UV spectrum the earth's
> atmosphere is quite good at blocking a large percentage of the energy
coming
> through.
>
> http://squ1.org/files/wiki/solar/spectral-content.gif
>
> -Kenneth
>
>
>
> -----Original Message-----
> From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org]On
> Behalf Of John Swindle
> Sent: Sunday, July 27, 2008 1:43 PM
> To: dprglist at dprg.org
> Subject: RE: [DPRG]Wall-E -> 1GHZ computers laser rangefinding
>
>
> Folks:
>
> I disagree with one of the comments about using IR instead of
> visible light, supposedly because there is too much visible light
> noise in the environment. A similar reasoning error is made when
> thinking about using 40KHz for sonar, thinking that there's less
> sound noise around that frequency. Just because we can't hear or
> see something says nothing about how much noise there is at those
> frequencies. Indeed, there's lots of IR noise. Everything is
> somewhat hot. And for sonar, the harmonics of our machines and
> our squeaky sneakers are well above our range of hearing. The key
> to rejecting noise is the modulation.
>
> Back to my passive sonar stuff now. (I'm using audible sound so
> that I can debug it with my ears instead of always depending on
> the microphones and calculations.)
>
> John Swindle
>
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