You gotta go to Home Depot and get some 5000k Philips LED bulbs. 60w equivalent.
They're half the wattage of the cfl.
They're twice the lumens of your CFLs.
Plants love them. Check out my Strawberry Kush mother Grow journal. Did the whole thing under Philips 5000k led bulbs.
To be clear, I'm not quoting him to advocate that particular light so much as LED tech generally.
The LED light bulb advocates pretty much convinced me to switch from CFL to LED light bulbs for small/cheap/first-time grows or for seedlings. Just thought I'd pass that along.
As for the original question: That looks like enough light to grow a pretty plant, but for good flowers and potency, you will want at least twice that much (and that's just for one smallish plant). Cannabis loves light, and there is a huge difference between enough to grow and enough to thrive.
<edit> Wait, it's the old question of 120 watts equivalent (i.e. about 15 watts of actual power) or an LED bulb that actually uses 120 watts from the wall? That photo looks like it might even be the latter. What's the lumen rating? The real 120 watt units put out a ton of light (10,000+ lumens) but are expensive ($100+) and probably overkill for a small grow box (and might even be too hot).
That looks like a nice budget setup. Remember that you can and should get CFLs withing just inches of your plants for best results. The light from the tubes is diffuse, not focused, so you want it as close as possible (and because they don't get hot, you can get them really close).