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# Physics Question of the Day - Combining Wavelengths

#### spacecowboy

##### New member
What would result if you were somehow able to combine the wavelengths of typical diode frequencies?

445nm + 532nm + X(n+1)nm = (XYZ)nm

Would the resulting beam wavelength be an average of the contributing wavelengths or the sum of wavelengths? What about the beams energy? Would it follow suit?

Could this result in extraordinary colors?

The most practical method would be using reflective medium causing the beams to converge into one, but could you also do this using some sort of collective device to detract the beams and cause them to mix (think of shining your laser into a glass rod). This second method would obviously not be used when trying to combine beam energies.

Anyone?

#### Gryphon

##### New member
Combining blue and green will give you blue and green. Unfortunately the waves will not merge into one and give you a brand new wavelength. Although when veiwing the dot you'll see a cyan or turquoise looking dot, that fact remains that the color you are seeing isn't really there, you only see it becasue thats what your eyes and brain make of seeing the two different colors in the same spot.

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#### Things

##### New member
Yes it is possible using dichroic mirrors:

However the wavelengths do not change, you simply end up with overlapping wavelengths which tricks the eye into seeing another colour, there is still only the 3 original wavelengths.

#### DrSid

##### New member
It's not a matter of summing wavelengths .. but of summing perceptions of them. For close wavelengths of same intensity you get perception of wavelength between them. Average of two wavelengths weighted by their intensity will work in many cases.

But as perception of colors goes, it all breaks down into how much individual RGB cells in the eye are stimulated. So it works for combination from red to green and from green to blue. Orange simulates both red and green receptors in the eye .. so simulating red and green receptors will induce orange perception.

But combining red and blue will create purples and violets which are out of the spectrum. There is no single wavelength representing them. Also combining red, green and blue will give you white, which again has no wavelength. Most colors cannot be represented by single wavelength, which is why such formula cannot exist, at least not in general scope.

Check this diagram: http://en.wikipedia.org/wiki/File:CIExy1931_fixed.svg
Clean single wavelength colors are on the curved border of the color space. Violets are on the bottom straight border. Most colors lie somewhere in the middle. You can also use this graph for combination of perceptions. Pick 2 points, draw a line between them. Divide the line in ratio of intensities .. and you get perceived color.

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