RT info:eu-repo/semantics/article T1 Photosynthetic active radiation, solar irradiance and the CIE standard sky classification A1 García Rodríguez, Ana A1 García Rodríguez, Sol A1 Diez Mediavilla, Montserrat A1 Alonso Tristán, Cristina K1 Photosynthetic active radiation K1 CIE standard skies K1 Solar irradiance K1 Electrotecnia K1 Electrical engineering AB Plant growth is directly related to levels of photosynthetic photon flux density, Qp.The improvement of plant-growth models therefore requires accurate estimations of the Qp parameterthat is often indirectly calculated on the basis of its relationship with solar irradiation, RS, due tothe scarcity of ground measurements of photosynthetic photon flux density. In this experimentalcampaign in Burgos, Spain, between April 2019 and January 2020, an average value of the Qp/Rs ratiois determined on the basis of measurements at ten-minute intervals. The most influential factor in theQp/Rs ratio, over and above any daily or seasonal pattern, is the existence of overcast sky conditions.The CIE standard sky classification can be used to establish an unequivocal characterization of thecloudiness conditions of homogeneous skies. In this study, the relation between the CIE standard skytype and Qp/Rs is investigated. Its conclusions were that the Qp/Rs values, the average of whichwas 1.93 0.15 mol J�����1, presented statistically significant di erences for each CIE standard skytype. The overcast sky types presented the highest values of the ratio, while the clear sky categoriespresented the lowest and most dispersed values. During the experimental campaign, only twoexceptions were noted for covered and partial covered sky-type categories, respectively, sky types5 and 9. Their values were closer to those of categories classified as clear sky according to the CIEstandard. Both categories presented high uniformity in terms of illumination. PB MDPI YR 2020 FD 2020-11 LK http://hdl.handle.net/10259/5687 UL http://hdl.handle.net/10259/5687 LA eng NO Spanish Ministry of Science and Innovation, grant number RTI2018-098900-B-I00 and Consejería de Educación, Junta de Castilla y León, grant number BU021G19 DS Repositorio Institucional de la Universidad de Burgos RD 11-dic-2024