Incandescent bulbs yield a light that is high in the red end of the color spectrum, producing tall, but usually spindly growth. Fluorescent lights, which are usually cheaper to operate, emit more blue light, yielding short, stocky plants. The “best” fluorescent light to use depends on the plants you’re growing, how much space you have, and your budget.
Best Quality of Light
You want lots of blue light for growing plants, especially seedlings and clones. Choose “cool” or “cool white” bulbs; it will say so on the package. Color temperature is measured in Kelvins (K). Temperatures of 5,000 K are green-blue “cool” colors. Temperatures of 2,700 to 3,000 K are yellow-red “warm” colors. Check the package to see the color temperature of a particular fluorescent light.
Best for Larger Plants
Buy a light that gives you about 20 watts per square foot of plants that you are growing. If your plants are from 18 to 24 inches high, use two or three fluorescent lights above your plants. The effective range should be about 24 inches. If you have flowering plants, place the tubes 6-12 inches away to produce blossoms.
There is no one best fluorescent for everyone's needs. Look for those lights that say they are “plus” or yield “high output.” You have essentially five choices, depending on the light needs of your plants.
“Cool white” or “warm light” fluorescent tubes first appeared on the market first and are cheapest to buy.
“Daylight” fluorescent tubes more closely approximate sunlight than cool white or warm light tubes. You can sometimes find them in department stores and in hardware stores.
The original grow lights emitted light in both the blue and red portions of the spectrum. This range of light matches the visible light absorbed by chlorophyll. They emit almost no light at all in the rest of the light spectrum and so cast an eerie purplish glow. They look like dim psychedelic lights.
Wide spectrum lights appeared on the market more recently. These emit color bands of the blue and red that are wider than those produced by earlier models of fluorescent grow lights. The light looks pink.
Full spectrum tubes emit light in every range of the spectrum, including a small amount of ultraviolet light. These tubes, with a color temperature of about 5,000 K, attempt to imitate the equatorial sunlight at noon.