A multidirectional spectral measurement method and instrument to investigate non-image-forming effects of light

Light directionality, spectrum and relevant radiometric or photometric quantity are believed to be 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 enabling the 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 200-1100 nm with ∼5.7 nm pixel resolution. Application of the MuS facilitates a better understanding of the non-image-forming light characteristics of space. The MuS was tested with stable electric lighting as well as dynamic daylight conditions and proved reliable to perform continuous spectral measurements for different directions simultaneously. Results of the test measurements in dynamic daylight conditions show differences in the spectral distribution and measured irradiance of up to 30 times in different directions.