sure the blackstar 240 is really a 130w output light. Many (most) led manufacterers advertise the total chipset/diode capacity of their lights. What most people don't know is that if the lights were driven to their full capacity it would fry the boards out very quickly this is why they use step down transformers and regulators to run the chips at a percentage of their true capacity. This is how a "240" light manages to pull 130w of power draw and output. The same can be said of my Hydroponics Hut Pro-Grow 180s, they also draw 130w of operating power and output.
One of the only companies I've seen that advertises their output wattage is Grow LED Hydro. So, to elaborate a blackstar 240 is really a 130, their 180 really about a 80-90w light. If you want to put more than one plant under it, opt for the 240.