On the possible observations of intergalactic or halo clouds in optical emission

The discussion of the problems of observation of tenuous intergalactic and/ or halo clouds in recombination emission is presented. We elaborate the pos sibility that clouds are illuminated only by metagalactic ultraviolet radia tion flux, and assume some plausible values for the parameters determining the physical conditions in such objects. A simple, semiqualitative approach may give specific observational predictions for the two major signposts of fluorescent emission: Ly alpha and H alpha lines. We conclude that H alpha detection of Lyman-limit systems at low redshift is within present observa tional capabilities. Open questions for further research are put in a conve nient framework.