A method is proposed for estimating the spectral radiance factor of fluorescent objects by using visible lights and an imaging device. We use neither an ultraviolet light (black light) nor a monochromator, but use an easy imaging system consisting of a multi-band camera and two ordinary visible light sources. The imaging system can provide fluorescent characteristics at every pixel of an object surface. The camera outputs are modeled using the Donaldson matrix with the two factors of reflected radiance and luminescent radiance. An algorithm is then presented for estimating both radiance factors from two sets of spectral images of the camera outputs, captured under two light sources. This solution method is based on use of two sets of observations under the known illuminant spectra to obtain two unknown components. The feasibility of the proposed method is examined in experiments using fluorescent paints in detail. The light sources of an incandescent lamp and an artificial sun lamp are selected as a set of suitable light sources. The accuracy of the estimated radiance factors is confirmed.