It is interesting to remember -- always -- what sort of light source your characters have. Or don't have. You reach automatically for what is natural, and naturally you're just wandering around in the light --aren't you? Except of course, you aren't.
It got skewered in The Tough Guide to Fantasyland so I'm not alone, and indeed, I don't think I've ever put anyone underground without providing for lights or noting that it's dark down there -- but sneaking around on a moonless light at a location where all the torches are far away. . . .
To be sure, this is especially a problem for fantasy writers who do not endow their characters with magical light sources. It's a lot harder to light a fire (lantern, candle, etc.) than you may have been led to believe. But if you're sneaking about, you can't have your own light source; you might as well have it spell out: "Sneaks here! Come stop them!" (Tolkien wisely never had his characters light a fire at night without pondering whether it would be seen and what that would bring about.)
On the other hand, your eyes can adjust to a lot less light than you might think. Walk by starlight, perhaps. Then, where would you go nowadays to verify that fact with all the light pollution about? I remember how hard it was to find something lit only by moonlight to verify that you can't see color by moonlight. (You can't! It's so very, very weird. Though if you know the color of what you are looking at the memory can blur with what you actually see and make it hard to be sure.)
(Don't, however, use Joyce's excuse for Finnagans Wake: "They say it's obscure. They compare it, of course, with Ulysses. But the action of Ulysses was chiefly during the daytime, and the action of my new work takes place chiefly at night. It's natural things should not be so clear at night, isn't it now?")