Light directionality, spectrum, and relevant radiometric or photometric quantity are believed essential factors influencing the magnitude of non-image-forming effects. In this paper, a measurement method and an instrument (the multidirectional spectroradiometer - MuS) is proposed, which considers different light incidents and spectra simultaneously, therefore, enables measurement of light characteristics relevant for non-image-forming effects. The MuS consists of four spectroradiometers measuring in different directions. Four spectrometers using optical fibers were configured to measure the spectral irradiance within a wavelength range from 200 to 1100 nm with ~5.7 nm pixel resolution. Application of the MuS facilitates a better understanding of the non-image-forming light characteristics of spaces. The MuS is tested with stable electric lighting and with dynamic daylight conditions and is proven reliable to perform continuous spectral measurements in different directions simultaneously. Results show a substantial difference in measured radiation magnitude and spectral distribution in different directions, which suggests varying impact on non-image-forming effects.