Luminescence is the "spontaneous emission of radiation from an electronically excited species not in thermal equilibrium with its environment", according to the IUPAC definition.  A luminescent object is emitting "cold light", in contrast to "incandescence", where an object only emits light after heating. Generally, the emission of light is due to the movement of electrons between different energy levels within an atom after excitation by external factors. However, the exact mechanism of light emission in "vibrationally excited species" is unknown, as seen in sonoluminescence.

कम तापमान पर उत्सर्जित होने वाले प्रकाश को संदीप्ति (Luminescence) कहते हैं। यह वस्तुतः 'शीत वस्तु विकिरण' का एक प्रकार है।