spectroradiometers

Spectroradiometers are instruments that measure the spectral distribution of radiant power from a light source or scene as a function of wavelength. They yield a spectrum in measurable physical units, such as watts per nanometer per square meter for irradiance or radiance. They focus on absolute radiometric quantities rather than relative reflectance, and are used in lighting, solar, and color science applications.

Most spectroradiometers combine an entrance aperture, a dispersive element (diffraction grating or prism), a detector array (linear or area CCD/CMOS, photodiode array, or PMT), and signal processing. Light is dispersed into a spectrum and detected across channels. Wavelength calibration uses known emission lines; radiometric calibration converts detector responses to physical units using calibrated standards. Key specifications include spectral resolution, wavelength accuracy, radiometric accuracy, and dynamic range; stray light and temperature sensitivity are important limitations.

Two main configurations exist: array-based spectroradiometers capture the full spectrum in a single exposure with fiber input or integration into a system, while scanning instruments use a monochromator and a single detector to sweep wavelengths with typically higher resolution. Integrating-sphere setups measure total spectral power from a source, whereas directional measurements obtain radiance for source metrology and imaging systems.

Applications include characterizing LED and lamp spectra, solar-simulator and solar-cell testing, color rendering assessment, display backlight metrology, and sensor calibration. Calibration relies on traceable references to national or international standards to ensure spectral responsivity is known across the range. Limitations include stray-light effects, detector nonlinearity, and the need for careful wavelength and radiometric calibration for accurate absolute measurements.