blomma wrote: Derek
I will try to give you some insight on growing under lights from years of experience in doing so.
All fluorescents are not the same. Grow lights are made up of wavelengths within the red, orange, yellow, green, blue, green, and yellow of the spectrum that are suitable for plant growth that incandescent bulbs don't have. Plant lights are made to resemble full sun very closely and contain the wavelength in colors that plants need to grow. I don't want to get too technical so the above info is a short explanation.
The watt is usually related to the length of the fluorescent bulb. A 48" long tube will produce more light than a 24" one. The only information you need about a fluorescent light tube is that it is a grow light in whatever length you want.
You actually need 2 grow tubes placed side by side with 2-3" from each other in whatever lengths you choose. The reason is that there is a light fall off along the sides of the lights that is not strong enough to support plant growth. The strongest light is in the center. Place your sun loving varieties there and shade lovers more on the outer side. You can increase light at the edges by placing a large, white paper mat or board held up along the edges to reflect the fall off light back on to the plants.
HOW CLOSE? HERE IS A GUIDE:
This guide is suitable for plant lights, not for incandescent light. Measured from the top leaf.
Annuals, perennials, herbs, and vegetables---3-6" from the light
Cactus and succulents---3-6"
Observe your plants, if not enough light the plant will stretch upwards with leaves further apart. Move them closer to light source.
You can also increase light by using white paper, or aluminum foil, as I have done in the 3rd photo. As plants grow, I give them a "haircut" to prevent leaves from touching the tubes. This cutting won't hurt them.
Plants under lights are iris and daylily seedling from crosses I have made.