If you put the two 24" lights side-by-side and pointed them at the same spot, then you may well get ~74. If you put one on the left and one on the right, I'd expect something closer to 37 throughout the tank.
I have a real problem with some of these PAR statements. If you look at Marineland's PAR char
t, it gives the same rating regardless of size. Many give different ratings by size in the LED Compendium but I often cannot find the source data to verify the information.