There are three distinctive types of fluorescent light bulbs. Depending on the type of fixture, the ballast type it has, and the age of your fixture, you’ll be able to find one of these type bulbs more than likely. Though they range in length and width, they all do basically the same thing, light the room they are in.
T12 bulbs are the oldest type still in use in some fluorescent fixtures. These are bigger, bulkier bulbs and the least expensive to buy, although, they are not the most efficient bulbs. The biggest drawback of these bulbs is that they are warm weather bulbs. They need temperatures to be 60 degrees or more to start and operate properly. Below that temperature, the bulbs appear to flutter and are much dimmer as they start up. Prompting the need for a change to a more energy efficient type bulb, manufacturers have developed smaller and more efficient bulbs that save money after the initial purchase price.
T8 bulbs are more expensive than T12 bulbs, but will start much faster. They are excellent at starting at all temperatures, including temperatures below freezing. The starting temperature is set by the type ballast you have installed in the fixture that you buy. The ballast is responsible for starting the light fixture and determines the type of bulb required in each fixture.
T5 bulbs are a smaller version of their big brothers. Measuring only ⅝”, these bulbs are space savers but still put out the same amount of light as the larger bulbs. These bulbs are good for lower ceilings and countertops.
T5H0 bulbs are identical to the T5 bulbs with one exception, they are much brighter. In fact, these are high output bulbs are said to be twice as bright as T5 bulbs. They are a great addition in rooms with taller ceilings. When you are in a pinch for space, these fixtures can pound out the light for the space they need.