Luminous flux measures the total radiant power reaching a surface, but without regard to surface position: the power might be concentrated on only part of the surface or spread evenly across it. Irradiance (Ee) or illuminance (Ev) is the density of incident radiant flux or luminous flux at a point on a surface and is defined as radiant flux or luminous flux per unit area, as given by E = dφ/dA where (dφ) is the radiant flux or luminous flux incident on an element dA of the surface containing the point. The unit of irradiance is Wm−2, and that of illuminance is lux
The luminous efficiency of an electric lamp is the ratio of the luminous flux (in lumen) emitted by the lamp to the electric power (watt) given to it i.e. Luminous efficiency η = Luminous flux/Watt Note:- Lumens is the unit of measurement for luminous flux, which is the total amount of visible light emitted by a source. 1
Galvanized steel conductors do not corrode, and possess high resistance. Hence such Wires are used in telecommunications circuits, earth wires, guard wire, stray wire, etc.
EXAMIANS