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FrozenGate by Avery

808nm appears red to me like 650nm, why?

Alaskan

Alaskan

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When I see the dim spot from a 808nm laser pointer the shade of red looks much the same to me as a 650nm laser, why is that? I know the wavelength is hugely different yet I don't see much difference. I speculate it's because the red color receptors in our eyes can pick up a little of the energy but can't produce anything redder than 650nm, thus we perceive the only red we can perceive... What do you think?
 
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Well, you have three types of cones in your eyes. Green ones for green light, blue ones for blue light, and red ones for red light. The sensitivity for say, red light is different for each wavelength, and for some people, it can just stop around 650nm because red is then fully saturated, but the other types of cones are not even used. This is different for everyone of us and so for some people 660nm looks exactly like 685nm, while for others they are a world of difference.
 
When only the red cone is stimulated you'll see what your brain perceives pure red as. If 650nm only stimulates your red cone, then 650nm and up will all look the same barring nonlinear processes, oddball stimulations, or fluorescences.

At 660nm red looks pure to me. At 720nm it looks a bit maroon. At 780nm it looks redder. At 808nm it's very cherry red. At 848nm it looks like 660nm.

Everyone perceives wavelengths a bit differently, and everyone has different ranges they can see.
 
"thus we perceive the only red we can perceive... What do you think? "

Yeah, well, you can't beat that logic..........
 
I stripped apart my 532nm laser (cheap Chinese one, don't worry) and made it an IR burning laser. Honestly, i did not expect 808nm to look that red. It was fairly dimmer than my 650nm pointer, but the dot (actually it was bar-shaped, so not really a dot) was visible across the room (barely, but I could still notice it). I'm not sure if it looked exactly like 650nm, but it's very close to it
 
My converted 532nm to a IR burner does the same thing, makes a cherry red rectangle or bar across the room at about 225mw, after collumation. If I focus it tightly, it is a tiny red point, but when I shoot it through an expander, I can see it really is that bar shape.
 
There was a post a long time ago, by zyxwv99 if I'm not mistaken, where he included a link to a scientific paper explaining the reason. From what I remember it's pretty much what Sig said, at around 650nm it stimulates just the red cones, after that it starts to stimulate a bit of blue (hence the maroon), which goes up to 700nm and then drops back, which makes further IR look like more like "regular" red.

lazeristasUVISIR, I can see a dot of 850nm at around 8mW just fine.
 
Atomicrox said:
There was a post a long time ago, by zyxwv99 if I'm not mistaken, where he included a link to a scientific paper explaining the reason. From what I remember it's pretty much what Sig said, at around 650nm it stimulates just the red cones, after that it starts to stimulate a bit of blue (hence the maroon), which goes up to 700nm and then drops back, which makes further IR look like more like "regular" red.

lazeristasUVISIR, I can see a dot of 850nm at around 8mW just fine.
Click to expand...

Edit:
Found that post: http://laserpointerforums.com/f40/w...-light-you-have-seen-83438-2.html#post1207634

Do you remember the post about a russian? study that showed the extreme limits of human vision, even at unsafe levels? I'm looking for that next.
 
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A bit of research turns up a Color Plot for sub-400nm wavelengths. It isn't far into UV, but hey, it's something.

http://starklab.slu.edu/UVColorCircle.jpg
UVColorCircle.jpg


Now, if we could fine one for IR...
 
Pretty interesting, what's the number close to the 425? 400, perhaps?


A few months ago after hearing my ex-boss tell me he had cataract surgery I took a 365nm flashlight to work and tested him. He claimed to see a very strong lilac light with the eye that had the surgery, while the other eye could only see the usual "visible leak" from those flashlights. I believe he was telling the truth, he tried first with prescription glasses on and couldn't see the UV. When he removed the glasses he seemed genuinely startled to see the light.
I tried to get him to describe the color but he's not good at that :(
 
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