With an uncovered window I'd avoid a clear moonlit sky, especially that period when the moon is from half full onwards but if it has worked in the light or lack of light conditions you have already experienced then that's fine. A thick curtain drawn over the window on curtain rails as you would in a living room can still allow air to get in but prevents light entering as it has difficulty turning corners so as long as the curtain over laps the opening top and bottom and both sides by a few inches I'd think that you are pretty safe