2. Phosphors (commonly known as luminous powder) are usually divided into two categories: luminous powder with optical energy storage and radioactive luminous powder. Luminous powder for storing light energy is a kind of phosphor that stores light energy after being irradiated by natural light, sunlight and ultraviolet rays. Then it is slowly released in the form of fluorescence after the light is stopped, so it can still shine at night or in the dark, lasting for several hours to more than ten hours. Radioactive noctilucent powder is a kind of luminescent powder doped with radioactive substances, and the luminescent powder is excited to emit light by rays emitted by radioactive substances. This luminous powder has a long luminous time, but it is toxic and pollutes the environment. Use it with caution.