A student showed me his notes about photosynthesis. The notes spoke about electromagnetic radiation, and then said that a photon is a light bundle. I said to him that the idea of a photon is from quantum mechanics, which teaches us that we can make things only so small but not smaller. For example, the smallest drop of water is a molecule. Same with light. Light has energy, which can push things. We can make a small amount of light with a small amount of energy. There is a smallest amount that we can make, and this is a photon. This smallest amount depends upon frequency. That’s why ultraviolet light, with a higher frequency and so more energy, can damage your skin.