There are many places you can go wrong when it comes to garden grow lights for an indoor garden. The following advice will help you choose what grow lights to use in your garden, how best to use different lights, and some things to consider for safely using grow lights in general.
Only three types of lights are really cut out for growing plants. They are fluorescent grow lights, metal halide (MH) grow lights, and high pressure sodium (HPS) grow lights. Any of these can be used as a garden grow light.
Light looses it's "punch" quickly as it travels away from the bulb, so you have to keep the plants within a certain distance from the light. This is especially true with fluorescent lights.
In general, fluorescent grow lights are used for clones and seedlings.
Fluorescent lights will not burn your plants, so plants can be placed
as close to the light as you like. I usually keep the tops about 1 to 4
inches away. You may continue to use fluorescent grow lights for the
vegetative stage, but you will need to use more of them to keep the
growth nice and healthy. Plants grown under fluorescent lights usually
do O.K. as long as you keep them no further than 18 inches away from the
When it comes time to force flowering, plants grown this way must be given a few hours of high pressure sodium light each day for 3 or 4 days before they can handle the much brighter light (which is required for good fruiting/flowering).
Metal halide garden grow lights are also used for the vegetative stage of plant growth. Plant tops under metal halide must be kept at least 12 to 18 inches away from the bulb or they will burn (especially in the hot spot!). It also partly depends on what size MH light you are using....plants will have to be kept farther away from a 1000 watt light than from a 400 watt light. Metal halide lights will support nice, healthy plant growth up to 24-36 inches tall, (depending on the size light you use), and they will reach this height much more quickly than with fluorescent lights. Plants do not need to be "broken in" to sodium light when they are grown first under metal halide light.
High pressure sodium
High pressure sodium lights are used for the flowering stage of plant
growth (to produce flower buds, fruits, and vegetables), although I have
also used used Metal Halide lights for flowering with very good
results. You must keep the plant tops at least 12 to 18 inches from
these lights, or they will burn the plants. Once again, the distance
away from the light will partly depend on the size light you are using.
Plants in the flowering stage require much more light to develop properly compared to the vegetative stage. Your garden should finish with well-developed fruits (or flowers) on the top 12 to 36 inches of your plants (and possibly more), depending on a several different factors... visit the different pages on lighting for more info.
Before using indoor garden grow lights, you should consider a few things, such as...
All these considerations will have an impact on your overall garden design, so it is very helpful to have your garden design plan (at least a rough idea) before you begin.