Luminescence
3.6. Luminescence: emission (radiation of light) by a material in a non-equilibrium (excited) state due to energy from external influence (optical, electrical, mechanical, etc.) or due to energy of internal origin (chemical and biochemical reactions and transformations)
Source: "GOST R 12.4.026-2001. State Standard of the Russian Federation. Occupational Safety Standards System. Signal Colors, Safety Signs, and Signal Marking. Purpose and Application Rules. General Technical Requirements and Characteristics. Test Methods" (adopted and put into effect by Gosstandart Decree)