What do you have under the lights? If you can get by with just fluorescents, those are the least suspicious and the least likely to get stolen.

It will be tomatoes, kale, peppers, things like that. I was thinking about flourescents.

Don't worry about it.
leave the greenhouse unlocked. One of the 'punks' will probably sneak in one night to see whats up. then leave since there's no smoke to steal.
Don't sweat the sheriff either. they can't come bustin' up your greenhouse without a warrant and a light on at night is hardly probable cause.
I may be inclined to wire up something that'll alert me if someone steals my light but otherwise, don't worry too much about it.