A modular cube shaped light emitting diode (LED) luminaire that can be cascaded, or interconnected, to create a larger, higher power LED luminaire that produces more light than the modular LED luminaire is disclosed. Each modular LED luminaire comprises a housing, a heat sink, a power/control circuit board (PCB-A) and an LED circuit board (PCB-B). An optional fan and a metallic heat sink are also enclosed inside the modular LED luminaire housing/shell. The modular LED luminaire provides optical expansion across interconnected modular LED luminaires. The LEDs and heat sinks are easily removable for defect replacement, LED light replacement and upgrade, without uninstalling the entire luminaire. Secondary side processor control of the feedback regulator allows sensor, radio module, user inputs etc. to reside on the “safe” isolated (low voltage) secondary side of the supply can then be used to safely make changes (an allowable UL approval) in the regulated output drive to the LEDs.