My eyes see 940nm+ ?

[Nate]

So I was playing around with a 760, 720nm stack and a 940nm torch. Decided to look at my eye, IR is safe right? Well my eye notices the light, but can't see any illumination. Brings up questions I hope someone knows.

 

 

 

 

[Andy Perrin]

Some things:

 

1) LED spectra are narrow-ish but they are not lasers. They are not a single wavelength and they can be spread over 40nm or so, frequently. 
 

2) Your eye gets progressively less sensitive as you go towards IR, but it isn’t a sharp cutoff. You might well be able to see a high intensity beam shining directly into your eye, but be incapable of seeing the much weaker reflected light off an object. This is is one reason we don’t test filters by shining an LED through the filter into the camera — even with fantastic blocking of OD5, an LED can still punch through, even though the same light source and OD of blocking would not be enough to screw up an image. Works the same with your eye. 
 

3) IR has mostly been associated with positive outcomes when shining in people’s eyes in the literature, but I still don’t think it’s good to tempt fate. If you can see the IR, that means the intensity must be HUGE. 
 

4) NEVER EVER DO THIS IN UV!

[Nate]

5 minutes ago, Andy Perrin said:

Your eye gets progressively less sensitive as you go towards IR, but it isn’t a sharp cutoff

Ahh ok, thanks Andy. I've never done uv in the eye. This was kind of an IF'y post anyway. I tried to delete it but not all got deleted. Thanks for the info

[ulf]

It is not a good idea to do this with IR either if the beam is reasonably focussed or collimated.

The damage function is mainly thermal to the retina and the eye is rarely quite stationary, but it is still a risk to be avoided.

[Nate]

1 minute ago, ulf said:

but it is still a risk to be avoided

Gotcha, wont be doing it again. I had the beam at it's widest. Probably a good thing too, is the battery died during test.

[Bill De Jager]

Quote

Humans can see bright infrared remote diodes through a two photon process.

This is a nonlinear process in which a cone in the eye absorbs two photons at essentially the same time, allowing you to see near infrared if it is bright enough.

Quora (may not be accessible without an account)

 

The author, Bill Otto, is a long-time laser expert who served for a time as a laser safety officer.

[Cadmium]

When testing these things use a full spectrum camera instead of your eyes.

Filters are usually based on their 50% transmission, their transmission extends far below the nm rating, so what you and the camera see can be something much less than the nm of the filter, especially when pushing it with extreme conditions.

Torch LED tests are extreme, like Andy explains above, they are intense and can drill though even strong OD.

 

 

[OlDoinyo]

I believe there were posts about this topic here in the past. If you see IR via a two-photon process it will appear green (half wavelength.) If it appears deep red that indicates residual single-photon perception beyond the nominal limit. Both mechanisms require a lot of intensity, and thus the light source should be treated with respect.

[Nate]

5 hours ago, Bill De Jager said:

Bill Otto, is a long-time laser expert who served for a time as a laser safety officer

Thanks for the read. This does answer my questions. It was just very strange that my pupils were closing up, and I detected no change in brightness like you would with a visible flashlight.

[lukaszgryglicki]

I can see IR laser 808nm red dot on the wall - very visible for me. Never ever tried to look at it directly (I kn ow that the topic is about LEDs). But if I can see this laser's dot then direct view will probably burn my eyes.

BTW: it burns matches, paper etc.

But 445nm laser (a blue/violet one) which is so much more visible, I can see laser beam in the atmosphere at the night and a dot on a wall 300m away.

 

 

[Andy Perrin]

The intensity of an IR laser is definitely enough to damage eyes if you can see the spot. It’s probably a few hundred milliwatts if it can burn things, particularly since many things reflect IR well. Anyway, point is that people can definitely see IR if you pump enough light out, but if stuff is catching fire, that’s a good indication of how insensitive our eyes are at perceiving it. Also what a bad idea it is to shine even an LED in your eyes, much less a laser!

[lukaszgryglicki]

808nm IR is 7W.

445nm is somewhere around 4W (it's a laser module that uses 220V, cooling fan - not the laser pointer). None of them can be pointed at eyes - both have Laser class IV warning.

[Andy Perrin]

Oh yeah, those are things you shouldn’t even be looking at without goggles on. 

[Bill De Jager]

Class IV lasers can burn skin and eyes nearly instantaneously, and seeing even a diffuse reflection may cause immediate retinal damage under some circumstances.  The latter would also apply if it's a diffuse reflection in IR. 

[Fandyus]

20 hours ago, lukaszgryglicki said:

I can see IR laser 808nm red dot on the wall - very visible for me. Never ever tried to look at it directly (I kn ow that the topic is about LEDs). But if I can see this laser's dot then direct view will probably burn my eyes.

BTW: it burns matches, paper etc.

But 445nm laser (a blue/violet one) which is so much more visible, I can see laser beam in the atmosphere at the night and a dot on a wall 300m away.

 

 

Seeing IR as green? I'd love to experience that someday, well that is if someone could assure me it wouldn't be the last thing I see.

[lukaszgryglicki]

I see it as a dull red, not green - I'm not observing reflections from shiny surfaces/mirrors etc, it is just a painted wall. Anyway - I have protection googles too.

I had those lasers 8 year already (bought when I returned from my Polar expedition where we played with LIDAR a lot). I know how to use them not too loose my sight :P

 

[Cadmium]

You are seeing high red, not green. None of these filters cut off straight down, their transmission cut off are all tapered.  You are going to see the higher red, which you don't see when mixed with other lighting because high red it overpowered by lower wavelengths, just like UV is by higher visible.
 

[Bill De Jager]

20 hours ago, lukaszgryglicki said:

I see it as a dull red, not green - I'm not observing reflections from shiny surfaces/mirrors etc, it is just a painted wall. Anyway - I have protection googles too.

I had those lasers 8 year already (bought when I returned from my Polar expedition where we played with LIDAR a lot). I know how to use them not too loose my sight :P

 

I wrote what I did as a warning to casual viewers dropping in who may not know these things.  Many site participants are very knowledgeable in the relevant subjects here as well as related subjects, but anybody with little or no relevant knowledge may browse the site at any time and not understand the risks some of these technologies carry.

[Nate]

So how the misinterpreted and different direction this post has gone, as for my original observation of my iris closing up when 940nm torch shinning in it, I have come to the conclusion out of the blue without further testing, that when I shined the torch, my camera's lcd lit up so much to cause my eye to see the bright screen for a split second and close up and me thinking that eyes react to invisible light. May or may not be right, but I'm going with it.  Thanks for the comments

[Andy Perrin]

Nate: heeeee! You forgot the part about x-rays bouncing off Saturn!

[Nate]

9 hours ago, Andy Perrin said:

Nate: heeeee! You forgot the part about x-rays bouncing off Saturn!

 I forgot a lot of stuff