If its 40 watts it isnt a T5, there is no such thing as a 40 watt T5 bulb, just letting all of you know.. T5 46 inch bulbs are 28 or 54 watts for HO
, there is no 40 watt T5, T8's are either split into two 24 inch hoods or one long 48 inch hood.
His is clearly one as he said, which means he has 1 T8 light.. 1T8 light is low lighting, you can only grow low light plants...
High lighting, would be something like 4x T5 high outputs over a 55-90g tank. Medium lighting would be more like 2xT5 high outputs or 4x T5 normal outputs. Im afraid even if you get a 2nd T8 your lighting is going to still be low light