when it comes to lights, especially LED, the wattage refers to the amount of power it will use, not the amount of light, nor how much of it will be usable.
Best option would be to look at reviews for the specific light, over a comparable distance to the plants so you can get a better idea... you can maybe work out from the number of lumens it says it is (if it does) and hope they all go into your aquarium, I doubt there's a PAR map for a kit light, and I'm not going to suggest you try to use a PAR meter to see how it does.
If you just want to grow plants but aren't too picky about how they look, standard inexpensive white lights will be fine, if you care more about the color of the leaves (and fish) then 'full' spectrum or fully configurable WRGB lights work well but are more expensive.. the Fluval light is somewhere inbetween white and WRGB (I do quite like them though, they are really well made)
