Language of Light
Spectroradiometers are most ideal for measuring spectral energy distribution of the light source, which determine not only the radiometric and photometric quantities, but also the colorimetric quantities of light. These instruments record the radiation spectrum of the light source and calculate the desired parameters, such as chromaticity and luminance. Dispersion of light is usually accomplished in spectroradiometer by means of prisms or diffraction gratings.
The exact CIE V λ curve and CIE colour matching curves are stored in the software and are used to process the data from the measured spectral energy distribution of the light source under test. Hence, the measurement error associated with photometers and filter colorimeters is avoided in spectroradiometers. However, adequate sensitivity, high linearity, low stray light, low polarisation error, and a spectral bandpass resolution of 5 nm or less are essential for obtaining good accuracy.
Non-thermal radiators, such as discharge lamps (which can be characterised by their non-continuous spectral energy distribution), and narrow-band emitters can only be measured with precision by means of the spectral procedure. When compared to three-filter colorimeters, spectroradiometers do have their limitations, in terms of speed of measurement, price and portability.