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2mW yellow visability vs 5mW blue at night

c0ldshadow

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hey , i was wondering.. at night time, in normal conditions

1. will the beam of a 594nm 2mW yellow be visible?

2. will beam of 473nm 5mW blue be visible?

3. which of the two above will be more visible?

4. if 555nm is the wavelength most visible to us, would i be right to think 594nm yellow is more visible since 594-555=39, and 555-473=82

thanks a ton for any help

regards
-avery
 



Razako

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They will both probably be visible if you are looking at the beam from the right angle and there isn't too much background light. I think the yellow would be slightly more visible but I am not sure about that.
 

BlueFusion

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Yellow would be more visible, however the extra 3mW would make the blue more visible.
 

knimrod

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At night and assuming dark adapted (scotopic) vision, peak luminous sensitivity of the human eye will be at 507nM. Therefore a 473nM laser should be much more visible than a 594nM laser.
 

Cyparagon

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With low light settings, you see with scotopic vision (primarily rod cells) where the peak is 506nm. The blue would surely win in the dark.
 

steve001

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Photopic vision would over rule scotpic vision in the case of artificial light sources, if power outputs are equal. Scoptopic vision sensitivity only works under ambient light conditions such at dusk or just before dawn.. Yellow would appear brighter as it's only 39nm away from 555nm whereas 506 is 49nm away from 555nm. You can see for yourself http://www.repairfaq.org/sam/laserioi.htm#ioicav2
 

knimrod

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Photopic or scotopic vision refers to a light or dark adapted eye.  If it's night, I think it would be safe to assume the ambient lighting conditions are dark.  Since the original question refers to brightness of a "beam" at "night", I believe scotopic vision would be prevalent.
 

darklandz

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ok i just found this veeery strange!
a little while ago, i thought id play with the blue and yellow lasers out of the window. i noticed that the beam is much more visible on the 20mw blue laser compared to the 593.5 0.6-2mw.
in saying that, the projected dot of the 0-2 yellow laser at roughly 50 meters is alot brighter than the dot of the blue laser. i would say the dot of the yellow laser is about 10% brighter to the eye than the 20mw blue.
there is no doubt in my mind, that if u had a yellow and blue laser of the same mW, the yellow would seem brighter to the eye.
conclusion - blue lasers up close look brighter than yellow, but at distances, the yellow is more noticeable.
(not sure if this has something to do with divergence)
strange :eek:
 

Switch

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Well, is the dot on the blue one bigger? :-? If it is, it definetly is divergence related.
 

scopeguy20

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You all know that the sky is blue due to shorter wave increased atmosphric scattering? Well in a long enough based observation, I would expect to see this effect. The opposite effect is red sunsets due to much less red light scatter. I don't have a true yellow yet, but, these things coulld be the effect you see. Notably my violet laser seems to disapear at just a few dozens of feet.
 

Cyparagon

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That's because our atmosphere scatters longer wavelengths more thoroughly. This is why Red beams are extremely difficult to see.
 

member02

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has anyone taken into account reliegh scattering on certain wavelengths better than others? this could make more photons hit the eye nearer the blue sprectrum, when the beam is being viewed.
 

philguy

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Cyparagon said:
That's because our atmosphere scatters longer wavelengths more thoroughly. This is why Red beams are extremely difficult to see.
Erm, really? I always thought shorter wavelengths (blue) are reflected stronger, as the daytime sky is blue (lot of scattering) whereas the red part hits the ground barely scattered, and at sunset, all the blue light has to pass through a great deal more of atmosphere, getting scattered along the way to the point of nothing arriving anymore, whereas red doesn't get scattered that much and you can thus still see the red part of the sun rise.


Yet I don't think that would matter so much, considering that due to the so-called planetary boundary layer, the visible part of a night sky's laser beam is only around 100m upwards, and raleigh scattering will probably not make such a big difference there.


Yet I wouldn't mind being sent both a yellow and a blue 20mW laser to try and verify :)
 




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