OOOO goodness,,, ferts is a whole other kettle of fish. LMAOIf anything in growing pot needs a ' torque wrench' it is ferts not lighting .
The apogee is among the best meters if you really need to know where lighting is at.
The apps are ok if you just wonder .
One way or the other you will learn to read your plants or have troubles no meter or app will fix ? They may explain the trouble ,but the plant was trying to tell you all along ?
Turning your lights up to a 'target ' number or per say following the mfg. instructions [ 6 inches @100% during flower] is a recipe for disaster.
You learn to push your plants by reading your plants .
I still have much to learn .