- Photoperiodism in plants and animals: the physiological reaction of organisms to the length of night or a dark period. Read more here: https://www.britannica.com/science/photoperiodism
- The biological clock: this is a natural timing device that regulates the cycle of circadian rhythms. These natural processes respond primarily to light and dark. Read more here: https://www.nigms.nih.gov/education/fact-sheets/Pages/circadian-rhythms.aspx
- Light-dependent magnetic compass: migratory birds have a light-dependent compass in their eyes that gives them information about the direction of Earth’s magnetic field and helps them navigate during migration. Read more here: https://www.sciencedaily.com/releases/2016/06/160606100519.htm
- Bioluminescence: emission of light from biochemical reactions within living organisms, such as the flash of a firefly. Bioluminescence is a type of chemiluminescence – simply, a chemical reaction that produces light. Read more here: https://www.nationalgeographic.org/encyclopedia/bioluminescence/