# Wavelenght of Visible Light?

nautica

## Main Question or Discussion Point

Wavelenght of Visible Light???

is it 400nm to 800nm
or is it
450nm to 750nm

thanks
nautica

Related Other Physics Topics News on Phys.org
Integral
Staff Emeritus
Gold Member
Not much difference. What is the variablity between different sets of eyes?

nautica
Which would be more correct. I realize there is not much difference, but for some reason my Analytical chem teacher put it on a take home final. I have seen it both ways and didn't think it mattered much either way but I would hate to miss it just in case he is picky. Btw, this part of the test is multiple choice, which makes it even worse.

Thanks
Nautica

dextercioby
Homework Helper
nautica said:
Which would be more correct. I realize there is not much difference, but for some reason my Analytical chem teacher put it on a take home final. I have seen it both ways and didn't think it mattered much either way but I would hate to miss it just in case he is picky. Btw, this part of the test is multiple choice, which makes it even worse.

Thanks
Nautica
Then he's a bonehead!! :surprised There are no specific rigid borders of the visible spactrum.Sometimes 780nm is considered red,but others think of it as infrared.The limit for violet can be lowered under 400nm,but nobody asks why.
If he rates your paper badly for that issue,then he's a pathetic loser.U should have the guts and ask him where the hell he saw those limits and why does he think of them to be right...

Daniel.

Gonzolo
Well, I'm quite familiar with the optics field and I've never seen 800 before, so I say b) "final answer".

Gonzolo said:
Well, I'm quite familiar with the optics field and I've never seen 800 before, so I say b) "final answer".
I've worked with lasers on both ends of the spectrum, and believe me, if it's bright enough you can see it. I'm color blind so I can't see that far into the red, yet even I have seen above 800 nm. I've also seen light @ 351 nm. Your eye sensitivity drops off slowly; there is no sharp cut-off.

That said, I believe 400-800 nm is the most commonly quoted range, so I think that's your answer.

Gonzolo
Then the problem is solved.

Astronuc
Staff Emeritus
Why not propose to the instructor to do an experiment? Get a tube of Ne or Ar and put an electrical discharge (current) through it.

Use a well calibrated (optical) spectroscope and both of you look at the emission lines.

See for reference - http://home.achilles.net/~ypvsj/data/elements/

The site provides the number of emission lines in the range 4000-7000 Å (400-700 nm).

I think I remember lines around 770 or 780 nm, and perhaps around 800 nm, but that was a long time ago.

Integral
Staff Emeritus
Gold Member
Laser Jock said:
I've worked with lasers on both ends of the spectrum, and believe me, if it's bright enough you can see it. I'm color blind so I can't see that far into the red, yet even I have seen above 800 nm. I've also seen light @ 351 nm. Your eye sensitivity drops off slowly; there is no sharp cut-off.

That said, I believe 400-800 nm is the most commonly quoted range, so I think that's your answer.
I am kind of interested in how you came up with the wavelength of the light you claim to have seen? I work with relatively powerfully (12W) UV lasers (355nm), all that we see is scattered light, or secondary emissions. Paper works fine, for the low power alignment beam, of course paper in the beam at full power emits a broad spectrum, mainly from the flames.

I remain skeptical.

Nereid
Staff Emeritus
Gold Member
Guys, at 351 or 355 nm, esp a 12W laser!, you are likely doing your eyes serious damage! IIRC, it's extended exposure to UV which is a leading cause of cataracts.

dextercioby is right about the weak sensitivity in the tails; Integral's onto something about individual variation ... it's well known there are two types of red (and green) receptors, with slightly different spectral sensitivities (tho only one type of blue); there are also differences in the numbers of receptors, the max width of pupils, and (for all I know) differences in 'threshholding' (that'd be deeper 'in' the human visual system than the receptors).

Integral said:
I am kind of interested in how you came up with the wavelength of the light you claim to have seen? I work with relatively powerfully (12W) UV lasers (355nm), all that we see is scattered light, or secondary emissions. Paper works fine, for the low power alignment beam, of course paper in the beam at full power emits a broad spectrum, mainly from the flames.

I remain skeptical.
Thinking about it, I think you may be right. The light I saw may have been florescence. It was a pulsed excimer laser with ~200 mJ per pulse, average power of a couple of Watts. For the most part, I was careful to keep my laser goggles on, but once or twice I had them off and you could see a bluish glow around the steering mirror (which directed the beam into a dye laser).

Does that mean it's probably not a good Idea to look at a blacklight? they give of UV do they not? Well, no more glow in the dark bowling allies for me!

DaveC426913
Gold Member
Astronuc said:
I've been looking at these with my monitor turned up and I think I can still see some light all the way up to 800nm. I guess I have really sensitive eyes eh? I'm being careful not to damage my eyes - I'm looking at my monitor with UV sunglasses!

:rofl: :rofl:

I think it is 400nm to 750 nm or you could say 400bill A - 750bill A.