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Figure 12.8 As photon irradiance is increased, utilisation of energy gives way progressively to dissipation of energy. Photosynthetic events shift from photochemistry, to external and then internal photoprotection and finally to photodamage. Their comparative importance for shade leaves and sun leaves is indicated. Photoprotection is especially well expressed in sun leaves acclimated to additional environmental and biotic stresses. (B. Demmig-Adams and W.W. Adams, Annu Rev Plant Biol 43: 599-626, 1992)