A study related to the weathering properties of wood in outdoor applications. Free radicais were generated in green wood by electromagnetic radiation, sunlight (short-lived radicals), and fluorescent light (longer-lived radicals in small amounts). In air-seasoned wood, free radicals were generated by all light sources (including UV) in air and in larger amounts (and longer lasting) in a vacuum. The decomposition of the free radicals is thought to lead to discoloration reactions. -- AATA