How many Orphek DIF-50 LED Pendants on 75gallon tank

[Beamooplah]

How many Orphek DIF-50, 50 Watt, 120 Degree LED Pendants should I use on my reef 75gallon tank?

Also, what is the word on the street on Orphek's? Are they reliable? Are the pendants the way to go?

Thank you, Shawn