Irradiancj

Irradiancj is not a standard term in physics and is commonly a misspelling of irradiance. In scientific usage, irradiance describes the radiant flux per unit area incident on a surface and is a radiometric, not photometric, quantity.

Irradiance (symbol often E) measures how much power from electromagnetic radiation arrives at a given area. It is expressed in watts per square meter (W/m^2). Spectral irradiance, Eλ, specifies the power per unit area per unit wavelength (W/m^2·nm). Total irradiance is the integral of spectral irradiance over all wavelengths. In radiometry, irradiance depends on the distribution of radiance from the light source and the geometry of incidence; it is distinct from illuminance, which is the photometric measure weighted by the human eye’s response and reported in lux.

Common measurement devices include pyranometers, which measure global irradiance on a horizontal surface, and pyrheliometers, which measure direct normal irradiance. Radiometers and spectroradiometers can provide spectral or directional irradiance data, useful in solar energy, climate studies, and atmospheric science.

Applications of irradiance concepts span solar energy systems, where irradiance determines potential power output, and climate research, where changes in irradiance affect radiative forcing and temperature. In astronomy and remote sensing, irradiance measurements help quantify radiation from celestial sources or reflected sunlight.

Notes: when encountering the term “irradiancj,” it is typically a typographical error for irradiance. The article above describes the standard radiometric quantity and its key distinctions from photometric illuminance.