Apparently you have a 10 gallon tank, and I assume it has a 15 watt incandescent light over it? If so, adding another 15 watt incandenscent light will not provide enough light for plants, but it will make the water get a lot warmer.
If that light has a 15 watt T8 fluorescent light, and you add another one, you probably will have enough light, at least for lower light demanding plants But, if that light has a T5HO 15 watt bulb (I don't know if there is such a size.) you might already have enough light for low light plants.
18 inch long, T8 fluorescent bulb fixture. Two of those would be 3 watts per gallon of standard T8 fluorescent over a conventionally shaped tank. So, my guess is that this would be moderate light, and with some CO2 you could grow most plants. The Hagen unit can use ordinary sugar water with regular yeast, and would give enough CO2 to have some benefits for a 10 gallon tank, but you now need a diffuser or reactor for that, unless it came with the Hagen ladder device.