I found with my old tank, that the lights provided all of the heat during the hot months. So, during that time the temperature did drop at night. I don't know if my current setup gets that much heat from the lights.
The reason why i was asking is I was reading Christel Kasselmann book Aquarium Plants and she was talking about it might be good for plants to allow for change because natural does it from day to night! It als may help out fish because they don't use as much o2, what do you guys think?
Hm -- I worry when someone says "it might help ...". The fish in the wild get exposed to night air too -- so "it might help to carry the aquarium outside at night!".
Most plants would likely prefer a lower temperature than the fish, but again most seem just fine at the higher temperatures. Of course it might help ...
I would not be too concerned, your temperature will likely fluctuate a bit anyway so just don't worry about it too much.
Now if someone said "we did comparative tests and the plants in the tank that ..... did better than those in the ... tanks, and we repeated the experiment a number of times" -- THEN I would take a serious interest in it.
Otherwise, if things look good don't mess with them.
I doubt you will find that much influence from lights alone day vs night, a degree or two etc is typical, outside temps can certainly influence growth rates, O2 levels etc, we see this during warmer seasons, summer etc vs winter cooler seasons etc.