When molecules absorb light, the light energy is transferred to the electrons in the molecules so that the molecules are promoted from the lower energy, ground state to a higher energy, excited state. The molecules will usually remain in the higher energy, excited state for a very short period of time before they return to the lower energy, ground state. As the molecules return to the lower energy state from the higher energy state, they must lose energy. Most molecules lose this energy in the form of vibrations or heat but some molecules will lose some or all of this energy in the form of light. The wavelength and amount of light that is emitted by such molecules can be measured with a spectrofluorometer. Spectrofluorometric measurements of molecules are usually more specific than absorbance measurements because fluorescence depends on both the wavelength of the light absorbed by the molecule and on the wavelength of the light that is emitted from the excited molecule. Fluorescence measurements are also more sensitive than absorbance measurements so that lower amounts of material can be detected.