T5 Vs. T8 Fluorescent Blubs

Fluorescent lamps are one of the most common lighting systems in household use all over the world. They are cheap, energy-efficient, easy to replace and handy. There are different kinds of fluorescent light bulbs such as T5, T8, and T12. These bulbs differ in wattage, energy consumption and other factors.

  1. Diameter

    • The "T" refers to "tubular," the shape of the lamp. The 5 or 8 means the size of the tube in 1/8s of an inch. Thus, T5 is five-eighths of an inch, while the T8 is one inch in diameter. Also, a T5 is shorter by about two inches, so the T5 lamp uses up less volume of space than the T8 version, which is slightly larger and longer.

    Operation/Safety

    • Most T5 lamps function at frequencies higher than 20 kilohertz, so that their light flicker is faster than what may be noticeable by the human eye. This produces less eyestrain. The electronic ballasts used in T5's are quieter, without producing the characteristic hum of the magnetic ballasts usually found with T8 or larger lamps.

    Output/Bulb Life

    • T5 lamps have higher luminous flux--luminous radiant power rated in terms of lumens--than standard T8s per unit length. However, the total output of light is almost equal to that of the T8, and higher at certain temperatures. Standard and high output T5s have rated lives of 20,000 hours, comparatively the same as T8s. The newer technology T8s with prolonged life may last up to 10,000 hours longer than T5s. In general, lamps operating on extended cycles (on-off switching) last longer than those frequently switched on and off.

    Efficacy

    • The efficacy measure of lumen per watt is higher in T5s than T8s. A shorter, smaller T5 bulb can have more lumen per watt than a longer T8 bulb with more watts. For example, a 21 watt, 34 inch T5 has a lamp efficacy rating of 100, which is above that of the 32 watt, 48 inch T8, which has a rating of only 92 for those lamps using RE80 bulb, and 89 for those with RE70 bulb. According to the Light Efficacy Center, lamp efficacy is determined by "dividing light output by lamp power." RE80 and RE70 are types of T8 bulbs. RE80 bulbs produce more wattage of light per square foot than RE70 bulbs, resulting in brighter light output. A comparable 35 watt, 58 inch T5 has even a higher lamp efficacy rating and often produces more watts of brighter light per square foot.

    Brightness Retention

    • T5 bulbs keep more than 95 percent of their light output at 8,000 hours of use. Standard T8s may emit only 88 percent of their light as compared to when first used. Tri-phosphors and halo-tri-phosphors are the white coating in the glass which gives bulbs their white color and are responsible for the brightness of a bulb. Bulbs that only contain tri-phosphors in their coating may be more expensive because the bulbs retain the same initial brightness longer. T5's use only tri-phosphors in their smaller-diameter tubes while T8s have tri-phosphors and halo-phosphors.