A shadow band is normally a metal strip which blocks the direct normal radiation so as to allow a pyranometer or other solar radiation detector to measure only the diffuse sky radiation. It can be made out of other materials as long as they do not transmit light at the wavelengths you are observing. This was designed for a open-source variable angle spectrometer by the [Michigan Tech's Open Sustainability Technology Research Group]( http://www.mse.mtu.edu/MOST). For similar see the Open-Source Lab: How to Build Your Own Hardware and Reduce Research CostsOpen in customizer, size for your application, export STL and print.on your RepRap.