This work extends our previous research on an original photochemical reactor - the electrodeless discharge lamp (EDL) inside a reaction mixture that generates ultraviolet radiation in the microwave (MW) field. This arrangement was found to be a straightforward solution for homogeneous as well as heterogeneous photochemical experiments that need to be carried out at higher temperatures. Here we report the emission characteristics (250 - 600 nm) of EDL as a function of temperature, MW output power of the reactor, EDL envelope material, and properties of solvents used in photochemical reactions. Relative intensities of the individual emission peaks were found to be largely dependent on temperature (in the region of 35 to 174 oC): the short wavelength bands (particularly the 254-nm peak) were suppressed with increasing temperature. Solvents absorbing MW significantly reduced the EDL emission intensity. It is concluded that the right choice of EDL envelope material and reaction conditions is essential for an efficient course of a photochemical process in this experimental arrangement.