My 2 cents: noctilucent specifically refers to a time of day. This says to me that it refers to anything that shines at night, for whatever reason. It would seem also to indicate something that shines exclusively, or nearly so, at night, just as nocturnal refers to what is normally active at night, and not normally during the day. This would seem to knock out "glow-in-the-dark" items, as the light for these can be activated at any time. Sunset clouds would be in, but only if late enough to qualify as "at night" (another argument entirely). Also in are lightning bugs, as these normally light up only at night. In also would be outdoor solar lights of any kind, as they are created in such as way as not to light up until nighttime. Out would be most ocean-living bioluminescent creatures which glow in any darkness, not just at night. :0)