NEED MORE LIGHT!

Yes you can run more lights in terms of watts/m2 (or ft2), but can you reject the heat that is generated? I live in a hot environment so this is often the main constraint, for example. If heat isn't an issue for you, then the cheapest and most proven option is to add a 600 watt HPS. Don't run for veg though. Too red and makes very lanky plants. If you have a bit more coin then I would go for 2x 315watt CMH, they have a nicer spectrum and more efficient than MH, but on PAR (hehe) with HPS in terms of raw efficiency. They are the closest to sunlight we can get except for maybe super-expensive plasma lights. They will produce more squat plants than HPS, as they have more blue in their spectrum that supresses lengthening. HPS is mainly red light which makes for very large plants in general. CMH have good UV output for excellent frostiness and aroma. LEDs are great but honestly you have to spend thousands to get something that performs the same as good old HID, so unless you grow using those LEDs for several years, they will not pay back on their investment.