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Author Topic: Why is blue light attenuated more than other colours?  (Read 1919 times)

Offline thedoc

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Jason Bright  asked the Naked Scientists:
   
Dear Sir

I am in Grade 10 at Wynberg Boys High School in Cape Town. I have been doing a Science Expo in which I tested the visibility of different colour lights and how far in the distance you can see an object.

I found out that yellow and green light is the best and a blue light had the least visibility.

I have been researching to try and find out what phenomenon causes yellow and green light to have the best visibility, but to no avail.

Could you possibly tell me why the yellow light is better than the blue light as it seems to have nothing to do with wave length or frequency?

Could it possibly have something to do with the human eye?

I look forward to hearing from you.

Kind regards

Jason Bright

What do you think?
« Last Edit: 14/06/2012 23:30:01 by _system »


 

Offline syhprum

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Re: Why is blue light attenuated more than other colours?
« Reply #1 on: 15/06/2012 22:28:49 »
There are two things you must consider while doing this experiment, are you trying to measure the sensitivity of the eye to various colours or the degree of attenuation different coloured lights suffer passing thru the atmosphere.
If you are trying to estimate atmospheric attenuation using yours eyes as the detector you should first adjust the power of light sources to compensate for the variable sensitivity of ones eyes or if it is this variation in sensitivity you trying to measure you should measure the actual power of your light sources with an appropriate meter and equalise them and then attenuate them so that they are just visible.
 

Offline thebrain13

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Re: Why is blue light attenuated more than other colours?
« Reply #2 on: 15/06/2012 23:00:20 »
just an fyi. the human eye is much more sensitive to green light than all the other colors. It's an evolutionary thing. We've got to detect all the stuff that might be hiding in the plants  :0
 

Offline RD

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Re: Why is blue light attenuated more than other colours?
« Reply #3 on: 15/06/2012 23:28:14 »
Jason Bright  asked the Naked Scientists:

I found out that yellow and green light is the best and a blue light had the least visibility.

I have been researching to try and find out what phenomenon causes yellow and green light to have the best visibility, but to no avail.

Could you possibly tell me why the yellow light is better than the blue light as it seems to have nothing to do with wave length or frequency?


The scattering of light by the atmosphere is wavelength dependent ...
Quote
Rayleigh scattering is inversely proportional to the fourth power of wavelength, so that shorter wavelength violet and blue light will scatter more than the longer wavelengths (yellow and especially red light).


http://en.wikipedia.org/wiki/Rayleigh_scattering
« Last Edit: 15/06/2012 23:37:46 by RD »
 

Offline Bored chemist

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Re: Why is blue light attenuated more than other colours?
« Reply #4 on: 16/06/2012 12:54:20 »
Oh goody! Proper science.
We have two suggestions to explain the observation that the blue light seems to have the lowest visibility.
It may be the response of the eye
http://en.wikipedia.org/wiki/File:Eyesensitivity.png
 or it may be due to the scattering for which RD has kindly provided the data.
We need to devise an experiment to see which is right.
I propose repeating the experiment again, but using red light.
If the effect is due to the fact that the eye is most sensitive to green/yellow light then the red light will behave like the blue light (both are far from the peak sensitivity) and red light will have low visibility like blue light.
On the other hand, if the effect is due to scattering then the red light will be much less affected and it will have the greatest visibility.

I really hope you get the chance to do the experiment and find out because I'm not certain what the real reason is.
 

The Naked Scientists Forum

Re: Why is blue light attenuated more than other colours?
« Reply #4 on: 16/06/2012 12:54:20 »

 

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