If the strip light is 24 inches long, the bulb is probably 15 watts. However, if the strip light is 30 inches long, the bulb is probably 24 inches long, and therefore, 20 watts. The newer T8 kind of bulbs have a 24 inch long version that is 17 watts, but it is unlikely that you have that kind. HTH. Josh Liechty jliechty at custom dot net