mWm2

mWm2 stands for milliwatts per square meter, a unit of radiant flux density or irradiance. It expresses the amount of optical power incident on, emitted from, or transmitted through a surface per unit area. In SI terms, the base unit is W/m^2, so 1 mW/m^2 equals 0.001 W/m^2. The mW/m^2 notation is often used when dealing with relatively small irradiances or when reporting measurements in laboratories and environmental monitoring.

The unit is used across radiometry and photometry to quantify how much radiant power arrives at a surface. While W/m^2 is the standard in many contexts, mW/m^2 is convenient for low-intensity sources or for detailed laboratory measurements, such as calibrated light sources, biological experiments, or sensitive detectors. Large-scale natural sunlight typically yields irradiances on the order of hundreds to about a thousand W/m^2, which corresponds to millions of mW/m^2, illustrating the wide dynamic range between common daylight and low-intensity sources.

Measurement and instruments involve radiometers, photodiode sensors, and spectroradiometers. Broadband instruments like pyranometers often report irradiance in W/m^2, while photometric or laboratory setups may present results in mW/m^2 for convenience or precision at low levels. Calibration requires traceability to primary standards and awareness of spectral response, since irradiance can vary with wavelength.

Applications span solar energy assessment, atmospheric and environmental monitoring, photobiology, and optical engineering. Understanding mW/m^2 helps quantify low-light exposure, radiative heating, and the performance of light-emitting devices under controlled conditions.