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Old 02-19-2012, 09:23 PM #1
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Default Relative Brightness Calculator, beam vs dot brightness.

Can someone who's a bit more educated than me explain the following.

This link is for the relative brightness calculator
Beam: (547nm 1mw) vs. (458nm 1mw)
You put in the wavelength and power and it compares them, it's really excellent but the only thing i'm wondering is how come the "dot" and "beam" are not the same?

For example: 100mw 650nm vs 100mw 445nm - the red "dot" is 3.6 times brighter than the blue dot, but, the red "beam" is only 0.8 times as bright as the blue beam. I find this remarkably interesting but not 100% sure how it works like that and why.


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Old 02-19-2012, 09:46 PM #2
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Default Re: Relative Brightness Calculator, beam vs dot brightness.

Rayleigh scattering is the process in which particles or mollecules smaller than the wavelength scatter incident light as it is traveling. Rayleigh scattering affects shorter wavelengths much more greatly than longer wavelengths, which is why the sky is blue - the blue light is scattered the strongest.

So, beam visibility is affected by rayleigh scattering where as the dot is not. Beam visibility is also affected by beam diameter and angle of observation.

Read up on Rayleigh scattering and you'll find out the angles at which it is strongest and weakest.
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Old 02-20-2012, 10:37 AM #3
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Default Re: Relative Brightness Calculator, beam vs dot brightness.

Scattering is one part of it, but it also has to do with how your eyes perceive the brightness of certain colors. Take a look at this table to understand how your eyes will perceive the brightness of a light source as a function of wavelength.
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Old 02-20-2012, 08:20 PM #4
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Default Re: Relative Brightness Calculator, beam vs dot brightness.

Quote:
Originally Posted by Sigurthr View Post
Rayleigh scattering is the process in which particles or mollecules smaller than the wavelength scatter incident light as it is traveling. Rayleigh scattering affects shorter wavelengths much more greatly than longer wavelengths, which is why the sky is blue - the blue light is scattered the strongest.

So, beam visibility is affected by rayleigh scattering where as the dot is not. Beam visibility is also affected by beam diameter and angle of observation.

Read up on Rayleigh scattering and you'll find out the angles at which it is strongest and weakest.
Excellent reply, after doing some study on that i found it very interesting!

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Originally Posted by Bionic-Badger View Post
Scattering is one part of it, but it also has to do with how your eyes perceive the brightness of certain colors. Take a look at this table to understand how your eyes will perceive the brightness of a light source as a function of wavelength.
Everyone who has a good interest in lasers should look at that because it's pure brilliant!! So much info on different wavelengths and mW and how we see them etc.
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Old 02-20-2012, 08:35 PM #5
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Default Re: Relative Brightness Calculator, beam vs dot brightness.

BB, you're right, but in this case I think the OP knew that and was merely asking why it makes a difference if you're comparing relative beam brightness to relative spot brightness. I.e. if you had a matched brightness of blue to green why don't the beams appear to be equally as bright.
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Old 02-21-2012, 02:20 AM #6
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Default Re: Relative Brightness Calculator, beam vs dot brightness.

Flourescense is also a factor... the dot of a 445 or 405 nm laser will appear brightly on most white (walll)apapers. With 405 nm this aspect is very pronouced... the beam may be hardy visible, but the dot on the wall probably is.

Sometimes its amazing to see what a fluorescent substance reveals in hte path of a 405 laser - and yes, its realy that powerful/harmful!
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