Red and far red light trigger many developmental processes in plants. Phytochromes are responsible for processes such as flowering in short and long day plants, stem elongation in response to shade and the production of flavinoids such as anthocyanin (blue-purple plant pigment). There are two forms of phytochromes; red light absorbing, P
r and far red light absorbing, P
fr. P
r converts into P
fr after absorbing red light and P
fr converts into P
r after absorbing far red light. Red light is generally available to plants during the daytime, and far red light available in the shade and during the night, therefore plants use P
fr and P
r levels to determine when there are changes in the length of daylight and when they are in the shade.