"The City Dark," a Documentary by Ian Cheney A documentary about light pollution that is entertaining and thought-provoking? It hardly seems possible, but that's what Ian Cheney has made in "The City Dark." Mr. Cheney's film is a personal lament for the star-filled night sky he experienced growing up in Maine, but it is neither sorrowful nor a rant; he somehow manages to give this engaging work a sense of humor. He also manages to make it smart, avoiding traps that might have snared other documentarians, like merely regurgitating the details of some local dispute over electronic signs or stadium lighting. Instead he and the people he interviews explore what our increasing inability to see the night sky means for us philosophically. "Seeing the universe around us tells us about our own part of the universe," says Jeffrey R. Kuhn, an astronomer at the University of Hawaii, "and to close that door, I think, would change the character of humankind entirely." Mr. Cheney reminds us of just how recent the phenomenon of an illuminated night is. Until a comparatively few generations ago, a campfire was the only noncelestial thing intruding on the daily darkness. Now, of course, our most inhabited places essentially have no night, and whatever human rhythms were tied to the natural cycle of light and dark may have been disrupted. Mr. Cheney is interested in more than the airy spiritual consequences of this. He also explores what it might be doing to health, noting studies involving night-shift workers and cancer. Other species are affected as well. Perhaps the film's most poignant footage is of newly hatched sea turtles in Florida that are confused about where the ocean is because of lights around the nesting grounds. "When we add light to the environment," says Chad Moore, the leader of a National Park Service team studying the issue, "that has the potential to disrupt habitat, just like running a bulldozer over the landscape can. Darkness is a necessary habitat for nocturnal animals. Mr. Cheney looks at a few attempts to use alternative lighting, including in the High Line park in Manhattan, but all in all, darkness seems to be fighting a losing battle. This film makes you want to go find a starry sky to camp under quickly, before it's all gone. Written, produced and directed by Ian Cheney; directors of photography, Mr. Cheney and Taylor Gentry; edited by Mr. Cheney and Frederick Shanahan; music by the Fishermen Three & Ben Fries; released by Argot Pictures. Running time: 1 hour 24 minutes.