What all that means is High Intensity Discharge (HID) lighting is the way to go to get the maximum out of your grow space.

I would Highly Recommend getting a 600watt HPS light and a 600watt Metal Halid conversion bulb that will run off your HPS ballast. Or a 600watt digital ballast that will run both MH and HPS bulbs ( a little more expensive but worth it). Or you can get a 400watt version of either one above ( I recomend 600w due to they put out almost double the lumins of a 400watt for only 50% more wattage [Ex. 400watt HPS 50,000 lumins, 600watt HPS 90,000 lumins]) these are not exact numbers but very close.

I see you live in Europe so unfortinatly I can't recommend where to get Lighting from But I am sure someone here can.

I hope this helps you understand better.

Best of Luck on your first grow.