Light as Wavelength
Isaac Newton demonstrated in 1666 that white light is a mixture of all colors by splitting sunlight through a prism. Each color corresponds to a wavelength of electromagnetic radiation: violet at 380nm, blue at 450nm, green at 520nm, yellow at 580nm, orange at 600nm, and red at 700nm. This simulation lets you build custom spectral power distributions and see how they map to perceived color through the CIE color matching functions.
Spectral Power Distributions
Every light source has a unique spectral fingerprint — its spectral power distribution (SPD). A sodium lamp emits almost exclusively at 589nm, producing a narrow yellow spike. A fluorescent tube has sharp mercury emission lines plus phosphor broadband emission. Sunlight approximates a smooth 5800K black body curve. The SPD completely determines the light's color, brightness, and rendering properties. Adjust the peak wavelength and bandwidth to explore how spectral shape maps to perceived color.
From Photons to Color
Your retina converts the continuous spectrum into just three signals via L, M, and S cone cells. The CIE 1931 color matching functions formalize this: they define how to integrate any SPD into three tristimulus values (X, Y, Z) that uniquely specify the perceived color. This three-dimensional reduction means infinitely many spectra can produce the same perceived color — a phenomenon called metamerism. It is also why RGB displays, with only three wavelengths, can reproduce millions of perceived colors.
Applications
Spectral analysis is fundamental to lighting design, display engineering, photography, astronomy, and material science. Color rendering index (CRI) evaluates how faithfully a light source renders colors by comparing its SPD to a reference illuminant. Display gamuts are defined by the chromaticity coordinates of their primary SPDs. Astronomers determine stellar composition by analyzing absorption lines in stellar spectra. Every field that works with light ultimately works with spectral power distributions.