Some atoms and molecules tend to first absorb photons of a certain energy (wavelength) and then emit photons of lower energy (longer wavelength). This phenomenon, called fluorescence, can sometimes change from one wavelength of visible light to another. However, fluorescence is most noticeable when the wavelengths of the incoming photons are in the invisible ultraviolet range of the spectrum, and the emitted photons are in the visible region of the spectrum (usually in the violet or blue range). The result is that the object appears to be emitting more photons in the visible region of the spectrum than it receives from the light source - while appearing "brighter than white".