The visible part of the electromagnetic spectrum is composed of radiation with wavelengths from approximately 400 to 750 nanometers. The blue part of the visible spectrum is the shorter wavelength and the red part is the longer wavelength with all color gradations in between.Spectral power distribution graphs show the relative power of wavelengths across the visible spectrum for a given light source. These graphs also reveal the ability of a light source to render all, or, selected colors.
Below see how a typical spectral power distribution graph for daylight.Notice the strong presence (high relative power) of ALL wavelengths (or the "full color spectrum"). Daylight provides the highest level of color rendering across the spectrum.
Compare the daylight spectral power distribution with that for a particular fluorescent lamp.The most obvious difference is the generally lower level of relative power compared to daylight - - except for a few spikes. All wavelengths (the "full spectrum) are again present but only certain wavelengths (the spikes) are strongly present. These spikes indicate which parts of the color spectrum will be emphasized in the rendering of color for objects illuminated by the light source. This lamp has a 3000K color temperature and a CRI of 82. It produces a light that is perceived as "warmer" than daylight (3000K vs. 5000K). It's ability to render color across the spectrum is not bad, but certainly much worse than daylight. Notice the deep troughs where the curve almost reaches zero relative power at certain wavelengths.
Here is another fluorescent lamp.This spectral power distribution looks generally similar to the one above except it shows more power at the blue end of the spectrum and less at the red end. Also, there are no low points in the curve that come close to zero power. This lamp has a 5000K color temperature and a CRI of 98. It produces light that is perceived as bluish white (similar to daylight) and it does an excellent job of rendering colors across the spectrum.