Grassmann's Law (optics)
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Grassmann's law in optics describes an empirically true law about human color perception. It was discovered by Hermann Grassmann.
If the test color is the combination of two monochromatic colors, then the observer's matching value of each primary will be the sum of the matching values for each of the monochromatic colors when viewed separately. In other words, if beam 1 and 2 are monochromatic, and the observer chooses R1 G1 B1 as the strengths of the primaries that match beam 1 and R2 G2 B2 as the strengths of the primaries that match beam 2, then, if the two beams were combined, the matching values will be R, G, B where:
Grassmann's law can be expressed in general form by stating that for a given color with a spectral power distribution I(λ) the RGB coordinates are given by:
