stupet

A stupet is a unit of luminous flux, a measure of the total quantity of visible light emitted by a source. It is part of the CGS (centimeter-gram-second) system of units. One stupet is defined as the luminous flux emitted by a light source with a luminous intensity of one candle, radiating uniformly in all directions into a solid angle of one steradian. The term stupet is derived from "stokes" and "pet," referring to the units of kinematic viscosity and electric current, respectively, in the older CGS system.

The stupet is rarely used in modern lighting practice. The SI (International System of Units) equivalent is the lumen. One stupet is equivalent to approximately 0.981 lumens, or more precisely, 1 stupet = (1/60) * (4π) lumens. This relationship arises because the candela, the SI unit of luminous intensity, is defined in terms of lumens per steradian, with 1 candela being equivalent to 1 lumen per steradian. Since a full sphere is 4π steradians, a uniformly emitting source of 1 candela produces 4π lumens. The historical definition of the candle also played a role in the numerical difference. While the stupet was a valid unit in its time, the lumen has become the universally adopted standard for luminous flux.