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.
3. Fertilize your geraniums once a month using a liquid fertilizer. An abundance of fertilizer will cause your geraniums to produce many strong, healthy leaves, but it will also prevent blooms from developing and may lead to a plant with minimal flowering. 1  You can also use a slow-release, granular fertilizer.tart geraniums from seed indoors. Early to mid-April is usually standard. Once the seeds start to sprout, you can move them outdoors. Just make sure that the last frost of the season has already passed.