A device for measuring solar spectral irradiance comprising: a diffuser disposed in front of an aperture of a diffuser cavity, the aperture having a first diameter; a body forming a first portion of the diffuser cavity comprising the aperture in a predetermined position; a first element forming a second portion of the diffuser cavity having a plurality of first collimator apertures, each first collimator aperture having a second diameter and positioned in a predetermined position on the first element; characterized by: a second element comprising a plurality of openings through the second element from a first face of the second element adjacent the first element to a second distal face, each opening of the plurality of openings having a third diameter and positioned in a predetermined position on the second element such that the plurality of openings are aligned with the plurality of first collimator apertures; a plurality of photodetectors, each photodetector of the plurality of photodetectors disposed within an opening of the plurality of openings within the second element distal to the first face of the second element; a plurality of optical filters, each optical filter having a passband of predetermined optical wavelengths and disposed between a first collimator aperture of the plurality of first collimator apertures and a photodetector of the plurality of photodetectors to filter optical signals coupled to the aperture of the cavity exiting the cavity via the first collimator aperture of the plurality of first collimator apertures. a diffuser disposed in front of an aperture of a diffuser cavity, the aperture having a first diameter; a body forming a first portion of the diffuser cavity comprising the aperture in a predetermined position; a first element forming a second portion of the diffuser cavity having a plurality of first collimator apertures, each first collimator aperture having a second diameter and positioned in a predetermined position on the first element; characterized by: a second element comprising a plurality of openings through the second element from a first face of the second element adjacent the first element to a second distal face, each opening of the plurality of openings having a third diameter and positioned in a predetermined position on the second element such that the plurality of openings are aligned with the plurality of first collimator apertures; a plurality of photodetectors, each photodetector of the plurality of photodetectors disposed within an opening of the plurality of openings within the second element distal to the first face of the second element; a plurality of optical filters, each optical filter having a passband of predetermined optical wavelengths and disposed between a first collimator aperture of the plurality of first collimator apertures and a photodetector of the plurality of photodetectors to filter optical signals coupled to the aperture of the cavity exiting the cavity via the first collimator aperture of the plurality of first collimator apertures. a second element comprising a plurality of openings through the second element from a first face of the second element adjacent the first element to a second distal face, each opening of the plurality of openings having a third diameter and positioned in a predetermined position on the second element such that the plurality of openings are aligned with the plurality of first collimator apertures; a plurality of photodetectors, each photodetector of the plurality of photodetectors disposed within an opening of the plurality of openings within the second element distal to the first face of the second element; a plurality of optical filters, each optical filter having a passband of predetermined optical wavelengths and disposed between a first collimator aperture of the plurality of first collimator apertures and a photodetector of the plurality of photodetectors to filter optical signals coupled to the aperture of the cavity exiting the cavity via the first collimator aperture of the plurality of first collimator apertures.