Are you talking about just a blue night-light or a specific product? If the latter, do you have a link? I rigged up a 7w incandescant red bulb for night viewing. Put it on a photo sensor (couple bucks from HD) so it comes on when the lights go off. Works fine. As far as I can tell, my nocturnal critters don't seem to notice it. I'm going to do something similar for my new tank, and was looking into using LEDs. Candy-cheap from Radio Shack, and it's a softer glow than the 7w bulb. I would also be able to string a line of them across the tank for more evenly distributed night lighting than I have now.