I have a 15 watt light in my 10g right now but I got another 8 watt light, they are both white, would that work?How deep is your tank - 28 watt sounds pretty weak. anubias and java fern will survive (not thrive) on extremely weak light but the sword is going ot want more light.
That should be good option.
only question is what is the tank height? And is the light full spectrum with white,red and blue leds?