Steam reforming of methane has been studied under direct illumination of a catalyst by concentrated light in an energy receiver/catalytic reactor unit with a light transparent wall. In such a reactor, the energetic efficiency eta of the light-to-chemical energy conversion is about 50-75%, both the specific rate r of hydrogen production and the specific power loading w are extremely high, reaching 40 N cm(3)/s per 1 cm(3) of the catalyst and 90-100 W/cm(3), respectively. Dependencies of r and w upon the incident power density and the methane conversion have been investigated. The data obtained are compared with those for nontransparent (steel) reactors as well as for reactors irradiated by high-power electron beam. Mechanism of the reaction rate enhancement as well as the influence of the reaction, catalyst and radiation nature on peculiarities of radiation-to-chemical energy conversion are discussed.