Many gardeners use fluorescent lights to start young vegetable and
flower plants during the spring or to grow certain houseplants all year
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 12/8 or 1.5 inches in diameter and are what most people are familiar
with. A T-8 is 8/8 or 1 inch in diameter, and a T-5 is 5/8 of an inch in
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. Our 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
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
them. Note that lamp costs are comparable between T-12’s and T-8’s.
The T-5 lamps are significantly more expensive and cost over twice as
much as either a T-12 or T-8.
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. b
By: Ward Upham