Photochemical Reflectance Index

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Photochemical Reflectance Index (PRI) is a simple measure of how efficiently plants use light for photosynthesis. It was developed by John Gamon at Stanford University. PRI responds to changes in carotenoid pigments in live leaves, especially xanthophylls. These pigments are tied to photosynthetic light-use efficiency, or the rate at which a leaf takes up carbon dioxide per unit of absorbed light. Because PRI changes with plant stress, it helps assess vegetation productivity and overall ecosystem health. It can be used with satellite data or other remote sensing methods to monitor vegetation. Applications include checking the health of evergreen shrublands, forests, and agricultural crops before they senesce. PRI is calculated from reflectance at 531 nm and 570 nm, and its values range from -1 to 1.