5500K still yellowish and able to grow low lighting requirement plants. You need to have 6500K-8000K to grow other nicer plants. And low lighting requirement plants will grow as well. ADA lighting tubes and bulb are all 8000K.

About the Watt, try to make it 3W per US gallon. If you have high lighting requirement plants, then you might need to have around 4.5W per US gallon.