Any chance you could put a lux meter at the water surface under the old light? Or at least to measure lux at the distance where the light would've been - it doesn't have to be actually over the water.
It would be very useful to you at least in theory to know how much different the two fixtures are. Me too. [emoji3]
It would be very useful to you at least in theory to know how much different the two fixtures are. Me too. [emoji3]