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Author Topic: How much colour perception is due to absorption or reflection?  (Read 2817 times)

Offline Ron Maxwell

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Ron Maxwell asked the Naked Scientists:
   
What is the difference in colour perception in the human eye from absorption, such as via anthocyanine in plants, and reflection, as in the visible spectrum?  Why are the primary colours in these situations different?

What do you think?
« Last Edit: 29/01/2010 11:30:02 by _system »


 

Offline yor_on

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As far as I know the absorption you think of when comparing it to the way a plant gets its color isn't there. the light hits the cones and the rods and depending on wavelength imports different amount of 'energy' which then is translated into what we call colors. What surprises me is that we all can agree on the same color for the same wavelength :)

Rods and Cones

---Quote--

Your eye has three different kinds of receptors with different frequency response curves. One of them is fairly well localized to the blue end of the spectrum. The other two have huge overlap with peaks in the green and yellow region of the spectrum, but both of them cover almost all of the visible spectrum. The one peaked at yellow is more sensitive to reds than the one peaked at green, but both are quite broad. Your brain process the intensity levels from these three kinds of receptors and tells you that you are seeing some color that may or may not be the same as some true monochromatic light. A hydrogen discharge tube produces only a few very distinct visible wavelengths. Your brain tells you the color you are seeing is something different from any one of those individual components.

---End of quote--

And it seems as if we by mixing different combinations of wavelengths might get what we think is the same color impression. But it still doesn't explain why we all find it so easy to define 'red' as the same 'color' if you see what I mean.


As I'm guessing that you see this absorption as some sort of direct transformation from light to color via photosynthesis.

---Quotes---

Plants absorb light with the help of Chlorophyll that is built into the thylakoids' membranes. This chlorophyll is green in colour and absorbs red and blue light. They do not and are incapable of absorbing green light. It is this fact, the inability to absorb green light, that makes the leaves of plants and chlorophyll appear green to the human eye. Plants require light energy for the process of Photosynthesis by which they convert this light energy to chemical energy. This energy is stored by plants in bonds of sugar. The process of converting light energy into a food source is unique to plants and some algae. No other type of organisms on earth can manufacture its own food. The chemical reaction that takes place during this process is represented as 6CO2 + 6H2O (+ light energy) → C6H12O6 + 6O2.

The majority of all plants are photo-autotrophs, meaning that they can synthesise food straight from inorganic compounds by making use of the energy obtained from light, of which the sun is the greatest provider.
==

The energy for photosynthesis is eventually received from photons that are already absorbed and engages a reducing agent, which in the case of plants is water, which releases oxygen as a by product of the process. The light energy obtained is then made into chemical energy, which in turn serves to perform synthetic reactions, that is, fixing carbon dioxide into carbohydrates, among other things.

---End of quotes--

==

As for reflection :)

Everything you see is a reflection from something, not even when you look directly in the sun will you see the 'direct original' photon hitting your retina, it will be a reflection from molecules and atoms in the atmosphere. All light we see are reflections as far as I know?

I'm trying to think of how to see an 'original photon' say from the Sun but I'm not sure how that can be done?
« Last Edit: 30/01/2010 20:42:24 by yor_on »
 

Offline Ron Maxwell

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Can a photon from a direct source be seen?  I would be interested in comments from the Naked Scientists on that point.
 

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