White light spectrum. Colorless or white light as perceived by human eye actually consists of many colors or wavelengths of light. Optical intensity as a function wavelength is called spectral distribution or spectrum. Shown here is the spectrum of white light emitted by an incandescent bulb filament. The spectrum was obtained by decomposing or spatially dispersing white light with a diffraction grating. Note that emission of the incandescent bulb covers visible spectrum continuously.