ISFH CalTeC - Sensors
Dr. Karsten Bothe
Tel.: +49(0)5151-999 425
The measurement of the spectral irradiance of light sources requires a spectroradiometer, which is a spectrometer calibrated with respect to wavelength and spectral irradiance.
Usually, a spectrometer is delivered with a wavelength calibration. This calibration is obtained by measuring distinct emission lines of known wavelengths and interpolating between them. However, in general, the measured spectrum does not represent the true spectrum of interest since all optical components along the light path (including mirrors, filters, diffraction gratings) as well as the detector have their own spectral characteristics and thereby affect the measurement results.
In order resolve this issue, a transfer function linking the arbitrary intensity scale of the detector to a physical meaningful scale is required. This transfer function is determined in a 3-step procedure:
In a first step we measure the known spectral irradiance of a 250 W tungsten halogen lamp in a distance of 300 mm from the light source for wavelengths from 300 nm to 1700 nm. The spectral irradiance of the lamp is traceable to a primary PTB calibration.
In a second step we calculate the transfer function to allow for measurements in absolute units of W/(m2 nm).
In a third step the correct measurement of the spectral irradiance of a reference light source is tested in an ISO 17025 certified procedure.