Fluorescence provides access to pigment-related data that are not provided by visible light images. Most prominently, chlorophyll emits fluorescence after excitation by light, but other pigments and breakdown products of chlorophyll can emit fluorescence, too. Chlorophyll causes red fluorescence that dominates the light emission due to high abundance of chlorophyll. The appearance of yellowish fluorescence hints at reduced chlorophyll content, or even absence of chlorophyll, as this signal is caused by breakdown products of chlorophyll or background pigments. Therefore, fluorescence imaging can be used as indicator for stress and senescence, with stressed or senescing tissues appearing yellow while intact tissue appears red.