Inspect the ends of your existing T5 tubes to determine what type of conversion kit you need. There are two types of connectors. Older T5 fixtures have a large nipple on each end of the light tubes. Newer T5 fixtures have two pins located on the end of the light tubes. Select the appropriate T5 retrofit conversion kit for your type of light tubes.
Slide the fittings from the conversion kit onto each end of the light tube T8 light tube. The T8 light tubes use two pins on each end. Align the pins with the holes inside the fitting and then slide the fittings onto the ends of the light tubes.
Place the pins or nipple into the couplers that hold the light into the fixture as you normally would. If you have pin style light tubes, rotate the tubes a quarter turn to lock them in place.