The absorbed energy is converted to heat energy. The scenario you mention with the LED is very close to the blackbody problem known as the ultraviolet catastrophe.. There is a Wikipedia article about it here. What happens in the situation you described is that the light proof box gets hotter.
Diagnosing rust on geraniums can be a challenge for growers. Rust begins with yellow spots on the underside of the leaves and can rapidly progress with brown fungal spores called pustules in the center of each spot. The pustules are raised up off the leaf surface and feel rough to the touch.
Camellia Flower Blight: This serious disease of camellia causes the flowers to turn brown. Flower blight appears in early spring when moisture is present and is caused by the fungus Ciborinia camelliae. Symptoms begin as small, brown, irregular-shaped spots on the flower petals. These spots quickly enlarge to cover most of the flower.