Tones of the same color. The use of monochromatic colors makes a room seem larger. You can achieve interesting effects by using different values (ie: light, medium, and dark), and intensities (ie: solid and muted) of a color together. Muted colors are softer and more sophisticated, plus they hide marks and other imperfections better than solids.
measured at a single wavelength (or frequency). The units depend on whether we are using wavelength or frequency: monochromatic flux on a wavelength scale is measured in W m-2 nm-1, whereas on a frequency scale the units are W m-2 Hz-1.