A PAR meter will tell you how much light is reaching the bottom if the tank has water in it.
A LUXE meter will read dry lights I believe ?? Just adjust distance to read where bottom of tank would be.
If the bulbs are old, swap them out, I try to swap my T5HOs out at least yearly.
You can buy LED
T5 equivalent bulbs...but no idea how theyíd work on aquatic plants.
Iím very pleased with some of the new cheap LED
panels in my Carnivorous Plant greenhouses