T5 fluorescent bulbs offer peak light output when the bulb reaches temperatures around 95 degrees Fahrenheit. T8 fluorescent bulbs offer peak output at lower temperatures. Their peak light output occurs when bulb temperatures reach approximately 77 degrees Fahrenheit. Ballasts designed for T8 bulbs are more efficient than T5 bulb ballasts. Ballasts linked with T5 fluorescent bulbs can take well over a minute to heat to proper operating temperatures. Perhaps one of the biggest differences between T5 and T8 lighting is size. T5 bulbs are designed to a thinner diameter than T8 bulbs.
Fluorescent T5 and T8 lights were designed to replace hotter-running high-intensity lighting. Fluorescent bulbs all burn much cooler than most other types of bulbs; little energy drawn from a T5 or T8 bulb is given off as heat. Four T5 bulbs offer approximately the same light output as a 400-watt metal halide or high-pressure sodium high-intensity discharge bulb. Both T5 and T8 bulbs can be employed to provide lighting for wide areas; however, T5 bulbs are often used in smaller lighting applications such as desk lamps.
T5 bulbs are available in a high-output variety. These efficient bulbs offer eight percent lumen depreciation over the life of the bulb. These bulbs are designed to burn for more than 20,000 hours of regular use. They are relatively new to the marketplace and are still linked with several design flaws. The ballasts traditionally fitted into high-output T5 bulbs can overheat, causing the bulb to fail.
T8 bulbs have been around for decades and have undergone several advances throughout the years. A Super T8 bulb offers approximately 20 percent higher efficiency compared to a traditional T8 bulb. They also are designed to last for about 4,000 more hours than older T8 bulbs or between 20,000 and 30,000 hours total. T8 bulbs introduced to the market in the 1980s contain around 40 mg of mercury, while newer Super T8 bulbs are constructed with less than 12 mg of the toxic substance.