Can you see if the light you already have has a K
number like 5600K on the bulb around the area where the watts are?
Did the ones you are buying have a K
= Kelvin Using Kelvin is a simple way to understand if the light will be in the correct spectrum for growing plants.
There are more technical (and accurate) ways to measure light [PUR, photosynthethically usable radiation], but K
rating will be enough to get the idea if it will grow. Lower than around 5200K is not usually good for growing low light plants. Better would be daylight bulbs around 6500K.
There are replacement bulbs if the one in the fixture - "20 watt 30 inch fluorescent light" - bulb you have isn't good for plant growth.