Hi, I have some T8 tubes over my tank. As they age, my understanding is that the light output from them starts to drop off. Does the spectrum of the light also start to change slightly too? From what I think I read a while back, plants don't really care too much about the spectrum (despite what product marketers tell us). Is that correct? And, as the lights age and the light weakens, wouldn't this be a good thing down to a point (lower CO2 requirements etc). How can I really tell when old enough is old enough? Scott.