Fluorescent bulbs come in two primary types, T8 and T12. Each type has its own set of advantages and disadvantages. Overall, fluorescent bulbs are known for their ability to provide bright and steady light over a larger surface area than a traditional bulb. The bulbs also tend to offer consistent lighting in a room, bathing the room in light.
One primary difference between T8 and T12 fluorescent bulbs is the size of the bulbs and their bases. While both bulbs come in standard lengths, commonly four feet, the number 8 or 12 refers to the difference in the diameter of the bulb. T8 bulbs are eight eighths of one inch, or one inch in diameter, while T12 bulbs are twelve eighths and have a larger diameter of one and a half inches.
Another area in which these two bulbs differ is in their energy usage. A T8 bulb is 32 watts, while a T12 bulb is 40 watts. This makes the T8 bulb a more energy-efficient bulb to use. A government standard known as the Federal Minimum Energy Standard requires buildings to start using energy-efficient lighting, favoring the T8 over the T12.
Both bulbs put out similar light output; although the T8 puts out slightly more light, the difference is not noticeable to the human eye. According to Philips, a maker of light bulbs and lighting equipment, a T8 bulb produces around 2600 lumens (the unit used to measure light output) while the T12 bulb puts out around 2520 lumens.
Over time the bulbs begin to lose their intensity and brightness. T8 bulbs have a slower period of decrease, losing only 10 percent of their initial brightness after 7,000 hours of use. In comparison, T12 bulbs can lose 20 percent, or double the T8 lose, after the same number of hours.
Ballasts are the parts of a light fixture that hold and power the fluorescent light bulbs. Electronic ballasts are more efficient at providing energy-efficient power to the bulbs and have multiple advantages over older magnetic ballasts.
Electronic ballasts can hold multiple bulbs and use less energy to power those bulbs. They work best with T8 bulbs for maximum energy saving. Part of their effectiveness is due to being better able to convert incoming electricity to the proper amount needed to power the bulbs, leading to less wasted energy.
While both types of bulbs do begin to lose some of their brightness after 7,000 hours of use, most people tend not to replace the bulbs until they begin to flicker or burn out completely.
Manufacturer recommendations suggest that users replace the bulbs every six to 12 months due to a slow decrease in brightness, but the difference is not usually noticeable to the naked eye. Bulbs running 10 hours a day daily can last up to two years before showing noticeable signs that they're in need of replacement.