A short explanation :
The "864watt" LED light probably has 288 of so called "3watt diodes" ( 864/3 = 288 pcs)
But in fact the '3W' LED diodes are not using 3watts of power :
The blue ones have a forward voltage of 3.3~3.6V when they are driven on 700mA, so the maximum power used by such a didode is somewhere between 2.3 ~ 2.5 Watts.
For the RED didodes, the forward voltage is much lower , at a maximum of 2.4V at 700mA, what gives a maximum power of 1.68Watts. But this LEDs have a short life when they are used at the maximum current of 700mA, so many manufactures drive them at ~600mA.
The white LEDs are in the same situation as the blue ones and the orange LEDs have the same specs as the REDs.
If this LED pannel draws only 516Watts, it means that the average power consumption per LED is around 1.8Watts ( which is closer to the above maths, depending on the number of the blue, red and white leds).
Wouldn't the actual wattage of the light be even lower once you allocate some of that 516 to the fans? I never really see that mentioned and have always wondered. How many watts do you think one of those fans pull? Thanks.