[en] A new simple method is proposed to design inexpensive A-class radiometers. Legendre-polynomial approximation is outlined to develop a multiple-filter radiometer, which permits an evaluation of solar power with a minimizable error. The method has been tested at the University of Calabria with an experimental apparatus, working in the wave-length range (0.39/1.1)μm. Preliminary results show promising developments for an instrument able to cover all the solar spectrum