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.
Spray the plants three times a week until you see no more caterpillars or new damage to your plants. The synthetic pyrethrins are more effective against geranium budworms than natural pyrethrins or other insecticides.pray your geraniums with insecticidal soap every other day as long as you see signs of pests, covering the tops and bottoms of the leaves. This helps control several pests, including aphids. The soap kills greenhouse whiteflies, which you can spot as tiny white dots on the bottom of leaves.