In your article on starting seedlings indoors, you recommend using fluorescent shop lights with cool white or daylight tubes. Are we being duped into buying those expensive specialty bulbs or are there other benefits I am not aware of?
No, you’re not being duped. Fluorescent tubes that are designed for growing plants indoors work exactly as advertised, providing plants with the specific wavelengths of visible light they need for optimum growth. It’s up to you to decide if the incremental improvement in plant growth is worth the premium price you’ll pay for the tubes—three or four times the cost of standard tubes.
Natural sunlight provides the full “rainbow” of visible light, from red through violet. Plants use mainly the red, blue, and violet wavelengths to photosynthesize and grow. The manufacturers of grow lights design tubes to concentrate light production in the areas of the spectrum needed by plants. So if you want maximum growth and are willing to pay the price, you’ll get the best results from these specialized tubes.
But other fluorescent tubes also produce the wavelengths used by plants—just not quite as much. I have had excellent results growing seedlings under regular cool white or daylight tubes. I often mix the tubes in a single fixture—for example, one grow light tube, one daylight tube, and two cool white tubes in a four-tube shop light.
It’s also important to remember that fluorescent tubes produce less light as they age. When tubes begin to dim, move them to basement or garage fixtures, where the quality of light isn’t essential, and buy fresh tubes for your seedlings. —Doug Hall