UV-ish Vs. IR-ish

[Atomicrox]

780nm and 808nm are nowhere near invisible. Heck, I can see a 850nm <10mW dot just fine.

 

[Emialias]

780nm and 808nm are nowhere near invisible. Heck, I can see a 850nm <10mW dot just fine.

yes but even then its still dim enough to be not as noticable when you get a reflection off of something. cant agree with 850nm because ive never seen it but i know i can see well past 730nm because i made a filter that block everything shorter than 730nm and i can walk around and see everything on a sunny day

 

[DashApple]

Fibre coupled diodes give a nice round spot with a short focal length lens , this is 940nm so not IR-ish

00022 1331 by TwirlyWhirly555, on Flickr

 

[Alaskan]

I've seen 808 nm, makes a nice red color, but what is happening is you are not really seeing the wavelength, the red cones of your eye are being excited by out of band energy to the point they are responding as if you are seeing red. That's my take on what is happening, anyone have something different?

 

[Emialias]

im pretty sure its just your red cones are sensitive to say, 808nm but just not very much. your red cones dont just drop sensitivity at 700nm, its just a downward gradual slope, and the longer the wavelength is the harder it is to see. it still triggers the red cone so you see red no matter what but its just dimmer. idk i feel like im just being redundant

 

[Alaskan]

The thought I had that the cones of our eyes responding to the 808 nm IR were doing so as out of band energy wasn't correct. In a way I am right due to the sensitivity of the eye falling off very rapidly at that end of the spectrum, but calling it out of band isn't the correct description, that's more of a radio technicians term, which I am, and probably why I saw it that way. When I went googling the subject, I found each of the RGB cones of our eyes are far broader in their responses to different wavelengths than I thought. More here:

From: Spectral Sensitivity of the Eye

​

The cone cells of the human eye are sensitive to 3 wavelength ranges which the eye interprets as blue (narrow, with a peak near 419 nm), green (broader, with a peak near 531 nm) and red (also broad, with a peak near 558 nm, which is actually more like yellow!).

Note: For scotopic night vision these wavelengths shift some.

 

[paul1598419]

I know for myself that 808nm looks like a deep red dot in low light. It is best when over 500 mW for me. I still use an IR camera to focus the beam, but at higher powers, it might work to just looks at the deep red dot. Haven't tried that, though.

 

[diachi]

I know for myself that 808nm looks like a deep red dot in low light. It is best when over 500 mW for me. I still use an IR camera to focus the beam, but at higher powers, it might work to just looks at the deep red dot. Haven't tried that, though.

Does the red disappear with glasses on for 808nm, specifically for 808nm, not for a shorter red wavelength too.

 

[Alaskan]

When I take the crystals out of a cheap 532 nm laser pointer and put a different lens on its output to focus the 808 nm to a tiny spot, I can see ~200 mw as a tiny red dot. If the dot is focused on black paper, it usually can produce a small wisp of smoke too.

 

[Emialias]

When I take the crystals out of a cheap 532 nm laser pointer and put a different lens on its output to focus the 808 nm to a tiny spot, I can see ~200 mw as a tiny red dot. If the dot is focused on black paper, it usually can produce a small wisp of smoke too.

i wanted to try that sometime but i figured it would be cheaper just to stick a cheap 300mw 808 into like one of those ebay pen hosts

 

[Alaskan]

It would probably be cheaper, I just used what I already had.

 

[paul1598419]

I have always looked at the dot from 12 to 15 feet and never used googles, so I don't know if it disappears with them or not. It's been awhile since the last time I did anything with IR.
I always used a black beam stop when doing this.

 

[Alaskan]

What I don't fully understand yet are the color cones we have for red, green and blue. Looking at the sensitivity graph I posted earlier, the red curve goes from 450 nm to 700 nm, what the? How can we tell the difference?

 

[Emialias]

What I don't fully understand yet are the color cones we have for red, green and blue. Looking at the sensitivity graph I posted earlier, the red curve goes from 450 nm to 700 nm, what the? How can we tell the difference?

say you only have red cones in your eyes. basically you can only see red. 450nm would just be red. a very dim red, but still red. so would 532nm and 577nm and 680nm. but we have blue cones too, and they are much much much more sensitive to 450nm than 532nm or 650nm.

another thought, think it like a digital image. each pixel has an rgb value. when say you have 255 of blue and 10 of red for a reigons rgb value, and you take all 255 blue out (kinda like having only red cones) you see 10 red, which is just not very much at all.

 

[paul1598419]

Since we are just taking guesses here, analog TV chroma modulation only has red and blue. The green vector is the difference inverted between the two. So, they used either I and Q modulation or Y-R and Y-B modulation. I don't think digital analogies work when dealing with human vision.