If there is a fuzzy shadow, the light level is medium. And if there is no shadow, light level is low. Special care is required to produce blooms. Poinsettia, kalanchoe and Christmas cactus flower only when day-length is less than 12 hours. However, most flowering houseplants are not sensitive to day-length.
Variegated leaves have pale or colored sections that contain no chlorophyll.
Chlorophyll is necessary for photosynthesis. Therefore, the rest of the leaf must be exposed to more light to compensate for the nongreen areas that cannot contribute to this life-sustaining process. Houseplants will grow toward the source of light. Phototropism describes the plant's tendency to grow toward light. If plants are not rotated regularly, they will become disfigured.