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Why does there appear to be banding when I look at pictures of the visual spectrum or light through a prism? Answered

It seems like when I look at one unit of the spectrum the color looks pretty much the same at opposite ends of the unit, but when I look at another unit of the same size at a different place in the spectrum, the color seems to change drastically from one side to the other.



Best Answer 10 years ago

Are you referring to the fact that the different "color bands" are not equal in width if you project a spectrum onto a plane surface? There are multiple reasons for that. First, if you don't properly align the output face of the prism with your projection surface, you're going to get foreshortening or/and keystoning of the image. That trivally distorts the relationship between position and wavelength. Second, our definitions (and perception) of color is not based on wavelength, but on the complex response of our visual system. The three color receptors in the eye -- the so-called "red," "green," and "blue," cone cells -- respond to fairly broad and overlapping wavebands. The mix of those responses within a given small neighborhood (you might say "pixel") is interpreted by the brain as different colors. A variety of "wavelengths", as well as the surround visual field, can lead to the brain percieving the "same color."


10 years ago

Are you looking at a picture of the spectrum's of white light (rainbow)? When you say "banding" it seems like you're referring to what's called an emission spectra. For example, if you look at a neon sign through a prism you would see "bands" of different colored light in different places separated by the absence of light. This is actually the electrons moving to higher energy levels within the atom then falling back down, when they do this they emit a photon of light in the constituent colors that make up the overall color of the neon.