A plant cultivation light source includes a plurality of light sources configured to be turned on or turned off depending on a selected plant and a growth stage of the selected plant, and a controller. The controller is operable to turn on the light sources during a light period such that the light sources are operable to emit a light having a spectrum with a plurality of peaks to the selected plant. The light period including a first period and a second period and the first period preceding or following the second period. The controller is operable to adjust the spectrum of the light to alternate the first period and the second period during the light period.