[Laser] Beacon to test a photodetector sensitivity limit

[Glenn Thomas]

At 10:29 AM 5/20/2007, Art wrote:
>I couldn't agree more Terry!

<snip>


>It's a very long story, and I won't bore you with ALL the details. 
>The short version is that I eventually migrated to my landlords 
>basement in the apartment building to do optical testing. It was in 
>the lower basement, 20 feet below ground level and there were no 
>windows or way for light to enter the room although it was a large 
>open area with lots of junk in the room. I went to this area 
>expecting it to be pitch black so I wouldn't have to worry about 
>stray light. But, using a photodiode without a lens, it was 
>painfully obvious that light was getting in somehow (the ambient 
>light level was 5 to 15 millivolts while the dark level (with a 
>cover over the PD) was well under 1 millivolt. I started using my 
>receiver as a probe to find out where the light was coming from. 
>Basically, light was coming from everywhere, even off my hand placed 
>a few inches in front of the photodiode! There was absolutely no 
>visible light anywhere in the room that I could detect with my eyes.

Since you were seeing IR of some sort, perhaps you were seeing the 
"black body" radiation (a'la Boltzmann) of the room itself?

73 de Glenn wb6w