Question

is light from a red and a green laser that combine into one beam that we would see as yellow physically different than light from one yellow laser that we would see as the exact same colour?

Answer 1

does that make any sense?

Answer 2

good question

Answer 3

if it was not different, then we should be able to create visible light by combining a UV laser and an infrared laser right? if it was different though then our eyes would not be able to see either, and we would not see the beam at all. My intuition agrees with the later, but I cannot seem to find the answer!

Answer 4

Yes human perception will "detect" Green in this situation. So how is this different from UV+IR ? Answer below

Answer 5

@richyw the human retina has 3 types of color sensitive cells. Although their exact sensitivity graphs overlap, the approximate "center of curve" correspond roughly to red region of visible light, green region and blue region. Their combinations with different intensities of detection give us the full gamut of the colors we perceive.
Now the integration and combining of these 3 different signals is done in the retina, the

Answer 6

AND in the brain part, called VISUAL CORTEX

Answer 7

These signals TOGETHER, are interpreted by the brain as the colour green. They are not , repeat NOt, added physically as their frequencies or other parameters. The process is purely computational in the brain cells.

UV + IR is not the same - because no signal will be generated by the color sensitive cells. No signal at all - results in no light perceived, let alone some color.

Answer 8

@UnkleRhaukus

Answer 9

@richyw

Answer 10

Want to go deeper ? Here
http://en.wikipedia.org/wiki/Color_vision

Answer 11

I see they did not bring today's supply of medals to the store , hmm ?

Answer 12

Surely the supply of answers is more useful, right .

Answer 13

when the red (635 nm) and green (532 nm) laser beams combined
we get a dichromatic beam {{635 nm), (532 nm)},

this is physically different to
a yellow monochromatic (593 nm),

even though our eyes could not distinguish the colour difference

Answer 14

First of al No, - our eyes certainly CAN distinguish the color difference, since the precise mechanism is quite sensitiv to DISTRIBUTION of wavelengths.
The beam is bichromatic. So ?

Answer 15

i think you misread the question Mikael

Answer 16

Thanks @demitris

Answer 17

No . Read the answers well. Also thanks for the medals.

Answer 18

@Mikael wrote:
"First of al No, - our eyes certainly CAN distinguish the color difference, since the precise mechanism is quite sensitiv to DISTRIBUTION of wavelengths. The beam is bichromatic. So ?"

This is true in general if the wavelength have been chosen randomly : they will appear with slightly different shades. But if these wavelength trigger the same response in the chromatic cells of the retina as the unique yellow wavelength, then the brain will have no way of interpreting them differently.
In order to achieve that, their frequencies AND their relative intensities have to be well adjusted.

If a well-calibrated camera films a sodium lamp, then the image displayed on a well-calibrated TV will appear of exactly the same colour as the original lamp.

Answer 19

In very simplified and "common knowledge" area - yes.
HOWEVER !
In REAL, DEEP and VERY INTERESTING REALITY - IT is MUCH MORE COMPLICATED and NOT SO @Vincent-Lyon.Fr
You would be surprised but colour perception is very much open and actively studied (and DEBATED) science.
For example the controversy on substractive color perception is still active.
To give you a taste here are books I would recommend FOR A START
http://www.amazon.com/Billmeyer-Saltzmans-Principles-Color-Technology/dp/047119459X/ref=sr_1_4?s=books&ie=UTF8&qid=1348311073&sr=1-4&keywords=color+science

http://www.amazon.com/Color-Vision-Colorimetry-Applications-Monograph/dp/0819483974/ref=sr_1_13?s=books&ie=UTF8&qid=1348311118&sr=1-13&keywords=color+science

http://www.amazon.com/Color-Imaging-Fundamentals-Erik-Reinhard/dp/1568813449/ref=sr_1_5?s=books&ie=UTF8&qid=1348311073&sr=1-5&keywords=color+science

http://www.amazon.com/Measuring-Colour-Imaging-Science-Technology/dp/1119975379/ref=sr_1_6?s=books&ie=UTF8&qid=1348311073&sr=1-6&keywords=color+science

http://www.amazon.com/Introduction-Color-Imaging-Science-Hsien-Che/dp/0521103134/ref=sr_1_14?s=books&ie=UTF8&qid=1348311118&sr=1-14&keywords=color+science

http://www.amazon.com/Color-Science-Concepts-Quantitative-Formulae/dp/0471399183/ref=sr_1_1?s=books&ie=UTF8&qid=1348311073&sr=1-1&keywords=color+science

http://www.amazon.com/Art-Technique-Digital-Color-Correction/dp/024081715X/ref=sr_1_8?s=books&ie=UTF8&qid=1348311180&sr=1-8&keywords=color+video

Answer 20

And to make this matter final : Sodium flame is NOT classified in proffessional colour imaging as pure yellow. It is somewhat orange in human visual coordinates.