Of the test light, subjects will double the Matching obeys the scalar rule: if you double the intensity People behave like linear systems in the color matchingĮxperiment.Of different settings that can achieve a match. No way to achieve a match for most light sources. Primaries there is only one way to set the knobs to get the match. Three primaries are always enough to match any test light.The lights in the two chambers are different. The test light SPDįrom the SPD of the combination of the primaries. Lights that are physically different can look identical.In almost all circumstances (the exceptions involve technicalities we won't discuss in this class), subjects can match any test light whatsoever as a sum of three primary lights, where all they can do is vary the intensity of each constituent primary. The subject's task is to adjust 3 knobs that set the intensities of the 3 primaries so as to match the test light as closely as possible. A small hole in the box allows a subject to see the colors from the 2 chambers right next to one another. A box is split into two chambers, one chamber has a test light, the other chamber has three primary lights (the 3 primaries can be almost any 3 light sources as long as they are different from one another). This figure is a diagram of the classic color matching experiment. Helmholtz performed a simple perceptual experiment to infer that there Nineteenth century scientists, first Young and then our old friend You can tell from the SPDs plotted below that both of those lights will have a reddish-yellowish appearance because most of the energy is at the long wavelengths. Any light can be characterized as the sum of a bunch of monochromatic lights, and that is what is plotted in the SPD graph (note that this is just like characterizing a sound as the sum of a bunch of pure tones). A light that contains only one wavelength is called a monochromatic light. Most lights contain energy at many wavelengths. By moving the slit and detector, one can measure the amount of energy at each wavelength. The diagram below of a spectro-radiometer shows a light source, a prism that splits the light into its separate components, a slit that passes only a narrow band of wavelengths (ideally it would pass only one wavelength), and a photodetector that measures how much light there is at that wavelength. The SPD can be measured using a spectro-radiometer. Spectral power distribution (SPD) is a plot of energy versus
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