Plant growth under different types of light can change how plants use sunlight for energy. Scientists studied how plants adjust the amount of two important parts of their energy system, called photosystems, in response to light quality. They found that the adjustment is mainly controlled by changing the amount of one specific photosystem. This change is influenced by a light-sensing protein called phytochrome B, but not by another signaling molecule as previously thought. In certain types of light, the plant may use up one part of the energy system more quickly, leading to the adjustment in photosystem amounts.