KC Gardens

Fluorescent lights for starting seeds: What's new?

Growing plants under light

Tip of the Week

Extension has long recommended the use of fluorescent lights for seed starting. The standard tubes or bulbs have been around for some time. These tubes provide high light for growing healthy, garden-worthy transplants just as long as they are placed close enough to the seedlings and left on for a sufficient amount of time.

This week I would like to share some wisdom from K-State Extension Master Gardener Coordinator Ward Upham, as he compares the advantages and disadvantages of using newer light fixture technology. So here’s Ward:

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, there are newer lamps that may be a better choice for some 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 diameter.

So, does a smaller diameter mean less light? Not at all. In fact, the T-5 is the brightest of the three. A T-12 lamp puts out 1,500 to 3,200 lumens for a 48-inch lamp. This lamp has a life of between 10,000 and 20,000 hours. The T-8 lamp produces 2,800 lumens and has a 30,000 - 40,000-hour life expectancy. The T-5 is rated at 5,000 lumens but lasts only 30,000 hours. Well, actually 30,000 hours is a long time. If you had your lamps turned on for 12 hours every day, it would take almost seven years to reach the 30,000-hour mark.

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 54 watts. This sounds too good to be true. Are there drawbacks? Of course there are. First is cost. Let’s start with T-5’s. Even though T-5 lamps produce more light, the lamps are much more expensive and harder to find. Also, you must have a special T-5 fixture, which is also very expensive. The 2-lamp fixture I located was priced over $250. Therefore, the T-5’s would not be practical for this use.

So, what about the T-8’s? First, you cannot use your existing T-12 fixtures for T-8’s unless that fixture is specifically rated for both. However, the price for T-8 lamps and fixtures is not that much more than T-12’s. That wasn’t always the case; it wasn’t that long ago that T-8’ lamps and fixtures were much more expensive.

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.

This is Dennis, again. I’d like to thank Ward for doing the research. This information will be very helpful to seed starters. I get questions this time of year about which light fixtures to use. (And in fact, we’ve already had our first question posted on the blog about starting seeds.)


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