After resizing the resistor values finally I powered the IR led array illuminator with 1A. The maximum radiant intensity at peak power should be 3740mW, according to the manufacturer specification. I assume this as the total optical power, that is radiated at 90 degrees total.
Maybe, If I could focus the light somehow the intensity in the center would be higher but still it seems to be enough for night flying.
I am not sure whether I reached the maximum power but now the garden is illuminated completely, I can see even the furthest point. I am a happy camper here