A three-channel dosimeter has been developed to measure solar radiation in the UV-B (280-315 nm), UV-A (315-400 nm) and PAR (400-700 nm) wavelength bands. A total of 31 instruments have been installed in Europe from Abisko in Northern Sweden to Gran Canaria, covering most light-climate zones. In addition, instruments are installed in India, Africa, New Zealand and South America. Seven of the instruments have been installed under water (each in conjunction with a terrestrial instrument), and two instruments are located in high mountain locations (Zugspitze, Germany and Sierra Nevada, Spain). The instruments use an integrating Ulbricht sphere and silicon photodiodes in combination with custom-made filters. All instruments are carefully calibrated to ensure a high standard of quality control and documentation. The software records all data ( three Light channels, external and internal temperature and depth for the underwater instruments) at 1 min intervals, displays them on a PC, stores the data on disk and transmits the data to the central server in Pisa (http:/ /power.ib.pi.cnr.it:80/ eldonet), where all available data can be seen in graphical form and downloaded as ASCII files. (C) 1999 Elsevier Science S.A. All rights reserved.