Illuminance is a photometric quantity that accounts for the wavelength-dependent sensitivity of the human eye. In contrast, irradiance is the corresponding radiometric quantity, representing the total optical power per unit area (in W/m 2) without being weighted for human. An optical power meter (OPM) is a device used to measure the power in an optical signal. Other general purpose light power measuring devices are usually called radiometers, photometers, laser power. The illuminance is a quantity defined in the area of photometry, which is used for quantifying the intensity of illumination, e. It is a unit of luminous intensity of a light source in a definitive direction. When you measure, you have to think about geometry, distance, and.
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