Which LED fixture are you running? If it's one of the major brands than BRS might have a video on the specific model and they use a spectrometer to match ecotech's spectrum for best coral growth on many fixtures. You might be able to replicate it. Here's an example on a video for the AI Primes. They even go one step further and calculate PAR readings at various distances from the light which is great info.
https://youtu.be/WWc3dUwQuWI?t=2m45s