Protection of a plant’s photosynthetic apparatus from the harmful effects of light. During periods of peak light intensity plants are able to utilize less than half the incoming energy. The surplus energy poses the risk of photooxidation, and the formation of highly reactive superoxide radicals that can destroy the cell’s chlorophyll and many other cellular components. Much of the excess energy is trapped and dissipated as heat by carotenoids of the xanthophyll cycle. Also, chloroplasts contain the enzyme superoxide dismutase, which scavenges superoxide radicals.