tilstrålingen

Tilstrålingen is the radiant flux per unit area incident on a surface from the surrounding radiative field, most commonly the Sun. In radiometry it is expressed as irradiance and measured in watts per square meter (W/m^2). Tilstrålingen is typically described as global tilstrålingen (the total irradiance received by a surface, usually horizontal), direct tilstrålingen (the beam from the Sun), and diffuse tilstrålingen (scattered light from the sky).

On Earth, tilstrålingen varies with time of day, season, latitude, and atmospheric conditions. The solar constant, about 1361 W/m^2, represents the solar flux at the top of the atmosphere. After atmospheric attenuation, surface global tilstrålingen can range from near zero to roughly 1000 W/m^2 under clear skies; direct tilstrålingen follows the Sun’s position, while diffuse tilstrålingen results from scattering by molecules and aerosols in the atmosphere.

Spectral tilstrålingen describes how irradiance is distributed across wavelengths and is typically expressed as spectral irradiance (W·m^-2·nm^-1 or W·m^-2·µm^-1). The total tilstrålingen received on a tilted surface depends on orientation; tilting changes the portion of the incoming radiation captured, compared with a horizontal plane.

Tilstrålingen is central to solar energy engineering, climate studies, and building physics. It informs the sizing of photovoltaic and solar-thermal systems, energy balance models, and daylighting calculations. Instruments used to measure tilstrålingen include pyranometers, which measure global tilstrålingen, and pyrheliometers, which measure direct tilstrålingen when pointed at the Sun; diffuse tilstrålingen can be inferred by shading or by specialized instruments.