Excessive light intensity, also known as radiance, will decrease a plant's capacity to convert energy into material, inhibiting plant growth. When a plant receives 50 percent of sunlight, it absorbs 25 percent of it. Receiving 100 percent, or full sunlight, decreases absorption to 10 percent. The result is decreased efficiency in carbon dioxide absorption, oxygen release and reduced fluorescence of chlorophyll. However, plants can minimize or prevent excessive damage by dissipating excess energy in the form of heat and radiation.
Fluorescence quenching is different from heat dissipation but can ward off cell damage for some time. During this process, when the chlorophyll molecules become overly stimulated by light intensity, radiation is emitted to dissipate excess energy, preventing cell damage. However, if light intensity continues unabated, damages cannot be reversed.
After prolonged exposure to intense light radiation, compensating mechanisms will not suffice. During photo-oxidation, energy converting pigments are destroyed, cells die and eventually the plant will die. Adaptation depends on where the plant originally grew. Shade-grown plants will probably not adapt to high light intensity. Other factors affecting adaptation include bend of leaf, carbon metabolism and other stresses at the time of high-intensity light exposure.
Saturating illumination is the technical term for the point at which light is no longer the limiting factor in the overall rate of photosynthesis. In other words, increased light intensity will not increase the rate of energy conversion. As discussed above, saturating illumination is the point at which damages can start to occur.