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.