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Photoluminescence: refer to the object need to be irradiated by light source of outside world, store the energy, then excite to lead to phenomenon of luminescence, roughly through three steps: light absorption, light storage and light radiation. Such as phosphorescence and fluorescence, long afterglow luminescence material is one of photoluminescence.

Long afterglow luminescence material: refer to after irradiated by natural light, fluorescent light, ultraviolet light, store the luminous energy, then emit this stored energy slowly in the form of fluorescence after stopping irradiation. So in night or in dark, luminescence still can be seen, duration time can be from few hours to ten hours. Strontium aluminate is common long afterglow luminescence material.

Excitation light source: light source which excite long afterglow luminescence material. According to different standard, excitation light source will be variant, Currently most standard is the use of standard illuminant D65.

Illumination: abbreviation of light intensity, refer to accept visible light flux per unit area. Illumination for short, refer to indicate the strength of light irradiance and the amount of illumination on surface area.

Lux: unit of illumination. Equal to illumination on one square meter surface generated by evenly irradiated by luminous flux of one lumen. Symbol LUX or LX, the illumination suitable for reading is 60lux.

Excitation time: lasting time of irradiating long afterglow luminescence material.

Afterglow: after excitation light source stop excitation, the stage of luminescent material emitting light.

Afterglow time: according to relevant standard, under stated light source, after stopping excitation according to stated excitation time, the time of emission luminance decaying to minimum brightness stated by standard.

Afterglow intensity: the luminance at every moment during afterglow time.

Candela: unit of luminance, symbol cd/㎡. The unit of luminance of long afterglow luminescent material is always milli candela, symbol mcd/㎡. Lowest brightness the human eye can perceive is 0.32 mcd/㎡.