Intensiteti

Intensiteti is a physical concept used in science to describe how strongly energy is delivered per unit area or per unit direction. It is not the total energy itself, but how concentrated that energy is in space or over an angle. Different fields define and measure intensities in related but distinct ways.

Radiometry divides intensity into several quantities. Radiant intensity I is the power emitted in a given direction per unit solid angle, with units of watts per steradian (W/sr). Irradiance E, or radiant flux density, is the power received per unit area (W/m^2). The total radiant power Φ is measured in watts (W). In lighting, luminous intensity is measured in candela (cd) and luminous flux in lumens (lm); luminous efficacy relates lumens to watts.

In acoustics, sound intensity I is the average acoustic power per unit area (W/m^2). For a plane wave, I is related to sound pressure p by I = p^2/(ρ0 c), where ρ0 is the ambient density and c is the speed of sound.

In electromagnetism, energy flow is described by the Poynting vector S = E × H, and the time-averaged magnitude ⟨S⟩ corresponds to the radiant intensity across a surface for extended sources. Measurements distinguish directional intensity, irradiance, and luminous quantities depending on whether energy, light, or human perception is considered.

Intensiteti thus serves as a unifying concept for comparing sources and fields across optics, acoustics, and electromagnetism. Its exact definition and unit depend on the context and the physical quantity of interest.