1. Fluorescence and multi-band light sources
When the extranuclear electrons are excited and jump to the excited state, the electrons in the excited state are unstable and always jump back to the ground state with lower energy. During the jump, the received energy will be released in the form of photons. . The phenomenon that a substance is excited to an excited state after being irradiated by a photon of a certain wavelength, and then jumps back to a lower energy level by releasing a photon of another specific wavelength
It is called photoluminescence phenomenon, and the photon lifetime usually released is less than 0.000001 second, which is called fluorescence; between 0.0001 and 0.1 second, it is called phosphorescence. If a substance can self-excite and produce fluorescence without external light excitation, it is said that the substance has intrinsic fluorescence. Another situation of fluorescence is to generate light waves with different wavelengths from the original light waves (usually short-wave excitations to generate long waves) under the excitation of an external light source, and the macroscopic manifestation is to emit another color light. The multi-band light source can provide not only an inverse light source for observing intrinsic fluorescence, but also an excitation light source.

2. Color separation principle
The principle of color separation is the prerequisite for the correct selection of the wavelength band (color light) and color filter of the multi-band light source. means that by selecting shades.