Old 05-19-2011, 08:00 AM #1
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Default What is truly visible?

I've searched the question, and came across a color chart which shows the typical 400nm-700nm visible surrounded by gray for a few 10s of nm on each side. I'd imagine there is individual variability, and this is what I'm curious about. Can any of you see beyond this spectrum? Is it typical?

I wonder if any visible light can be seen beyond this. Such as in lasers, the 10?0 IR lasers, and the UV lasers in the 300s. Also, florescent blacklight, is the purple which is visible below 400nm or is it just fluorescence/leakage of the filter?

I'd imagine UV lasers would make things visible even if not directly visible due to fluorescence.

When I got LASIK eye surgery years back (193nm I think) the lens looked like it would blink a strange yellow color.

When the semester starts back up, I'll see if I can go to a lab and look through a broad range spectrometer, or a few separate ones if I have to. And if there were some informative and thought provoking replies, I just may post my results



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Old 05-19-2011, 09:55 AM #2
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Default Re: What is truly visible?

It is all a matter of definition. You should first define 'visible', for example in terms of relative visibility. 650 nm may appear 10% the brightness of 555nm (the peak in the visibility curve) and is therefore considered visible by most. The problem is defining the limit of what is invisible.. 1%, 0.1%, or even 1 millionth?

Once you set a limit, you can check the standard Luminosity function - Wikipedia, the free encyclopedia or CIE tables, and come up with a visibility limit of scotopic and photopic vision.
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Old 05-19-2011, 12:13 PM #3
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Default Re: What is truly visible?

I know I can see 808nm somewhat, so it is visible, but just barely.
Longer than 1000nm must be truly invisible.
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Old 05-19-2011, 03:17 PM #4
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Default Re: What is truly visible?

I've seen as low as 365nm and as high as 850nm. Everything after 650 looks the same color, just with diminishing brightness. As you go into UV, the colors change slightly. 365 appears like a light-gray-violet to me.

So yes. You can see beyond this, but the intensity is so low that it contributes almost nothing to what you see from the regular spectrum.
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Old 05-20-2011, 03:08 AM #5
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Default Re: What is truly visible?

Interesting; the lumin. function was kind of what I was looking for, although it sets the standard 400-700nm boundary. According to this function, 543nm is only 70% the brightness of 555nm. So, we need to make a 555nm laser!

I wonder what the yellow color of the LASIK laser was; it is a class 4 laser, maybe bright enough for me to perceive 193nm... but the photoreceptors didn't know how to classify it perhaps.

Its embarrassing that I have a B.S. in medical biology and in the middle of my masters, and these mysteries/ignorance about light and perception remain.
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Old 05-20-2011, 04:30 AM #6
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Default Re: What is truly visible?

Most likely what you saw was some type of fluorescence in your eye due to it. 193nm is well outside human vision.. period. By a long ways. Plus that wavelength won't even make it through the cornea to even get to your retina.. Which is why it can be used for eye surgery. Otherwise they'd just be frying your retina's instead of reshaping your cornea.
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Old 05-20-2011, 02:10 PM #7
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Default Re: What is truly visible?

Here's a table that I find useful.
Sam's Laser FAQ - Items of Interest
Laser Visibility and Color
Relative Visibility of Light at Various Wavelengths

The following table lists the relative sensitivity of the Mark-I eyeball to wavelengths (including common laser sources) of light throughout the visible spectrum and somewhat beyond. Of course, not everyone comes equally equipped. Your mileage may vary (and the number of significant figures in some of these entries should not be taken too seriously)!
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Old 05-20-2011, 02:19 PM #8
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Default Re: What is truly visible?

Fluorescense within the eye seems like an explanation. In early research with x-rays it was also discovered that those are visible to the unaided eye, even with the eyelids closed. Researches descrbed it as an 'odd sensation of light originating inside the eye', and the were probably right. Now knowing the danger noone would repeat the experiment, but the observation stands.

Perhaps you should reconsider 'what is visible' as the question: 'what can i still see at an intensity that doesnt damage my eyes'. At least that gives some boudaries that make sense
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Old 05-21-2011, 02:50 AM #9
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Default Re: What is truly visible?

Benm, interesting, that reminds me of astronauts "seeing" cosmic rays as flashes of light. Although some rays aren't light (protons, even lead nuclei travelling close light speed), but some are gamma rays.

Also, radiation even has a "metallic taste", described by a survivor of a nuclear accident near the time of the Manhattan project.

I agree that the 193nm was fluorescence; although it could have been actual yellow light as some kind of indicator. It looked very localized, at the tip of the laser, not like it was causing my eye to glow.

The LASIK experience was kind of terrifying to me. Everyone was telling me how easy it was, so I wasn't prepared for hearing and smelling my eye burn with hundreds of crackles, and smoke. Although it lasted less than a minute, it was difficult and with a long term price of seeing halos when my eyes are dilated to a certain point due to darkness or ... whatever.
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Old 05-21-2011, 06:10 AM #10
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Default Re: What is truly visible?

Quote:
Originally Posted by hoon View Post
Benm, interesting, that reminds me of astronauts "seeing" cosmic rays as flashes of light. Although some rays aren't light (protons, even lead nuclei travelling close light speed), but some are gamma rays.

Also, radiation even has a "metallic taste", described by a survivor of a nuclear accident near the time of the Manhattan project.

I agree that the 193nm was fluorescence; although it could have been actual yellow light as some kind of indicator. It looked very localized, at the tip of the laser, not like it was causing my eye to glow.

The LASIK experience was kind of terrifying to me. Everyone was telling me how easy it was, so I wasn't prepared for hearing and smelling my eye burn with hundreds of crackles, and smoke. Although it lasted less than a minute, it was difficult and with a long term price of seeing halos when my eyes are dilated to a certain point due to darkness or ... whatever.
When I had LASIK the laser had blinking green and red lights near the aperture, and the doctor told me to stare at the green light. Perhaps the laser in your case might have had a yellow light on it. I really don't recall seeing anything else other than the blinking light (and not much at all during the actual lasering part) but do vividly remember the stench of my cornea vaporizing. Kind of like burning hair, which makes sense, as the cornea is made of a similar protein as is hair and fingernails. I guess I got lucky, had mine done a long time ago (1999) and no side effects to speak of.

As far as what wavelength can actually be seen, I do think that the established "borders" of visibility are a general guideline and obviously there's no hard cut-off point but rather a gradual fading regarding what wavelengths can be detected by the human eye. I have always heard that animals like cats and dogs cannot see red light but anyone who has a cat and a 1mw 660 or 690nm laser can attest to the fact they they can indeed detect that wavelength of light or they wouldn't chase the dot. Cats and dogs likely have a bluer shift in the wavelengths they can see (their eyes can best detect blues rather than greens as our eyes are optimized for) but clearly there is no hard and blunt cut-off with them either, even though they aren't supposed to see anything that's red. A 405nm might be blindinly bright to them, while it isn't to us. Apparently it's the same thing with human eyes and wavelengths "outside" our range of vision.
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Old 05-21-2011, 08:53 AM #11
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Default Re: What is truly visible?

Yeah keratin smells... heh. I do remember the doc telling me to stare at a fixed point but not the light, it was a metal thing near the laser. I was given a xanax 0.25mg only ten minutes before so I was entirely lucid and frightened during the procedure. The xanax didn't take effect until it had been about 20 minutes after the procedure was finished.

They kept acting like it was no big deal but I still asked for medicine. Those ignorant assistants.. the process was very anxiogenic, smelling, hearing and seeing parts of my eye go up in smoke.

As for the blue-shifted animals, interesting, too bad I don't have a purple laser to try that out with.
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