Many countries around the world have established scales for the measurement of optical radiation. These include luminous intensity, luminous flux, illuminance, luminance, spectral radiance and irradiance, spectral total flux, spectral responsivity, spectral reflectance and transmittance. Many countries also operate measurement accreditation services. Laboratories with accredited calibration services have been assessed by the accreditation body to ensure that the measurements are both traceable to national standards and carried out under a formal quality system. A calibration certificate from an accredited laboratory provides the user with confidence in the results contained within it, through the assurance that the laboratory is regularly inspected, its measurement results are subject to periodic audits and its measurement standards are fully traceable to national standards.
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