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Would small a LED light (probably just one in a 80 gallon tank) on the bottom of the tank during the night interfere with my turtle's life or upset it in any way?

I'm not sure what kind of light you're talking about, but they really don't need a night light. My res sleep in total darkness.

Would this lunar light provide any benefits? I also want to be able to watch my turtles without having to turn on the room's main lights during the night and disturb them. Should this even be a concern?

I was originally referring to this. Seems a bit useless now.

just use a small flashlight

There is a bulb that you can use as a heat source that puts out red light, barely visible, turtles are not supposed to be able to see it, ofcourse, I have never asked a turtle
Found here: http://thereptilecenter.com/Reptile-Sup ... ptile-Bulb

I used to use a red light but it seemed to me like it was freaking them out. As soon as I'd turn it on, they'd [----] their heads up to see what it was.

They were probably wondering where the heat was coming from.

Unless it's cool at night where you are, I'd forget using a light at night and let them sleep in the dark. You could flash a light on them as Steve suggested, but not for too long because they'll respond to the light and wake up (and why would you want to disturb them).

So it seems that I just shouldn't try to watch them at night. I figured with the lunar light, it'd be more natural. It may be comparable to a "real wild-life" setting. Oh well.

Trust me--they don't need it (and the moon goes in cycles, so even in the wild it wouldn't be out every night). Put your money into things your turtles really need.

jdub1107: I was thinking the same thing. Between the natural light in the room and the basking light etc being on for 10-14 hours (depending on the season) I thought of getting a moonlight so I can watch them in the evenings but I didn't know if it would disturb their sleep cycle. I also thought it would simulate the same "natural" sun/moon cycles of light.

Yes, I know they don't need the light at night and they sleep in the dark but it wasn't for them but I'd not be selfish and make them miserable for my pleasure.