I have found with the smaller tanks that watts under 15 is best....too high watts in shallow tanks can sometimes cause hair algae problems....the correct color temp is most important...6500k being ideal....I use the 7.5w 6500k bulb on my smaller tanks...
I usually can find them at walmart lighting section for under $8.00 each, I don't recall the brand-
They have a mini florescent screw in bulbs by Aqua culture-in the aquarium section that is 10w but I have never been able to figure out what the kelvin rating was on it... I have used that one on one of my 2gal NPT's and the plants grow fine, however, it also grow hair algae really well too....lol....but I don't stress over it...I just manually remove it as needed.
The Aqua culture Incandescent 15 watt twin pack-unknown kelvin-they have the clear bulbs and the blue bulbs they call planted tank bulbs....I don't really care for them especially the blue planted tank bulbs......waste of money IMO...
I do have some and use them on occasion but not alone-the clear ones look really yellow and the blue one seem too dark-I have one of each on a second light strip I use over one of my 10gal spawning tanks-but my main light strip has the correct color temp bulbs.
Watts are important and good for a general guideline-but truth be told...it the kelvin that drives the plant growth-photosynthesis.....watts is energy used to run the light bulb....sometimes its best to use the proper watts for what the light strip is graded to use-for safety.....too high watts can blow the light strip and cause hair algae.
With florescent bulbs you also want to change them out every 12 months-the intensity is lost over time and if the light strip also uses a starter-its a good idea to change them when you change the light bulb and they are usually pretty cheap-less than $2.00 for 2-be sure to get the right size based on watts.
The 11w 6500k CFL should be fine for a 2gal NPT
Look forward to pic.....