Photoinhibition is a reduction in photosynthetic efficiency caused by more light energy reaching a leaf than the photosynthetic system can safely use. In plants, it mainly affects photosystem II, one of the light-capturing systems inside chloroplasts, and can happen when PPFD is high, DLI is excessive, or light is strong while temperature, water, nutrients, or CO₂ limit carbon fixation.
Mild photoinhibition can be temporary if the plant dissipates excess energy as heat and repairs damaged proteins quickly enough. Severe or repeated photoinhibition can lead to chlorosis, bleaching, necrotic patches, stalled growth, or leaves that decline even though light is abundant.
Photoinhibition is not the same as sunburn. Sunburn is visible tissue injury, while photoinhibition can occur before obvious damage appears.
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