Many gardeners use fluorescent lights to start young vegetable and flower plants during the spring or to grow certain houseplants all year long. Traditionally, we have used fixtures with T-12 lamps suspended a few inches above the tops of the plants. However, T-12 lamps are fading away due to newer lamps that are a better choice for indoor gardens. These are known as T-8 and T-5 lamps. The number after the “T” refers to the diameter of the lamp in eighths of an inch. Therefore, a T-12 lamp is twelve-eights, or 1.5 inches in diameter, and are what most people are familiar with. A T-8 is eight-eights, or 1 inch in diameter, and a T-5 is five-eights of an inch in diameter.
So, does a smaller diameter mean less light? Not at all. In fact, the T-5 can be the brightest of the three. Another advantage for these newer lamps is they use less electricity per lumen. The traditional 48-inch T-12 is rated at 40 watts. However, there are newer styles of T-12’s that are 34 watts. The T-8 is rated at 32 watts and the T-5 at 28 watts.
This sounds too good to be true. Are there drawbacks? Maybe so or maybe not. First is cost, if you have to replace T-12 fixtures to convert to a T-8 system. However, newer fixtures may be able to handle either T-12’s or T-8’s. Therefore, if you purchased fluorescent fixtures in the last few years, check to see if they are rated for T-8’s before replacing. Note that lamp costs are comparable between T-12’s and T-8’s. The T-5 lamps may be more expensive so check prices before converting.
The question becomes, is it worth it? If you have a T-12 fixture that is rated for T-12’s only and are satisfied with your results, then maybe not. However, if you are investing in new fixtures or have fixtures that can use either T-12’s or T-8’s, then go with the T-8’s. They will use less energy, last longer and provide more light. Prices for T-5’s have been dropping, so you may want to consider them as well.
The newest technology is LED lighting. LED’s have several advantages over other types of lighting including durability, long life, a cool running temperature and more latitude in choosing specific wavelengths of light. Traditionally, they have been very expensive but costs are dropping rapidly. We are starting to use LED’s as supplemental lighting in the university greenhouses but would suggest only using them on a trial basis at home until you see how they perform for you.
-Ward Upham, K-State Extension Specialist