dark adapted

I understand that 505nM is the best for dark illumination in that one sees more at a given light level.

On a sunny day (Sat, 24 Oct 2009 01:15:08 -0700) it happened John Larkin wrote in :

Yes, but is it linear with current?

Can't tell with my eyes. It's interesting that I can see it light up from 10 mA to 1 nA, a range of 1e7:1.

If I were compulsive about stuff like this (what, me?) I'd get a good PMT or avalanche PD and build a long-tau lockin system and find out where the actual photon threshold is.

John

IIRC the eye can detect down to around 10 photons per second. Another interesting thing I read is that the skin gives off low levels of light ie we are slightly phosphorescent. Maybe a fully adapted eye can actually see that? Last time I was in aq cave with the lights out for a while I *thought* I could still see my hand move before my eyes.

Only if it has fungus growing on it. ;)

Cheers

Phil Hobbs

A few photons per sec per sq cm for the hand.

I did some testing a ways back at low levels for a(n)(on-going) project. Photometric output was dead-linear over at least a 1,000:1 forward current range. More, actually. Don't remember hard far down I went--it's deep in my notes.

Ultimately leakage dominates & wrecks things, but if you have a really fine LED, like those HLMP's, they're really very very good.

-- Cheers, James Arthur

Funny, I was just about to write in the Canadian Customs thread that I'll soon have the shop set back up & can make M that gizmo I promised. It's officially patent-pending. I've not forgotten, I'm just busy being Mr. Fix-It. (Plumbing/carpentry/masonry blah blah blah. But working with your hands is fun.)

-- Cheers, James Arthur

Please be advised that the human eye is a *lot* more sensitive than a PMT. Check it out with a Huggins lamp (mercury reed relay in center of coax to discharge attached coax line, charged via large resistor from variable supply). Good way to check plateau of PMT. In any event, use a 10nSec line and then crank down the voltage until the PMT stops "seeing" it....then keep on reducing the voltage until you stop seeing it. Guess what? (1) it was still bright as all heck, and (2) stops near

For a sufficiently crappy PMT. Good ones are several orders of magnitude better than the eye, and even more orders better than APDs.

Cheers

Phil Hobbs

And I can't connect my retina to a lockin.

John

Well, one photon / quantum sensitivity is certainly not an order of magnitude different than two.. Yes, the PMT i was talking about was made in the '70s and Hammatsu (and others) have improved on those by a large amount. So, maybe PMTs improved a lot - perhaps by an order of magnitude or better, but are the best quantum efficient (or close to that)?

Chlorophyll eye drops (just around the corner;)

A factor of 2 isn't going to replace night vision goggles, but it might be useful in marginal situations.

Cheers

Phil

"Foundations of Vision" by Wandell puts peak scotopic sensitivity at

(I recommend the book to anyone really interested in vision. The first half discusses measurements of the capabilities of human vision and the second half application of that information to design of lossy image encoding.)