When you grow plants indoors, sunlight from windows will rarely provide enough light for your plants to grow properly, and so you must use artificial lighting. If you only have a small area to grow plants in, high intensity discharge lights are the best type of lights to use because they provide high light output from small bulbs.
High Intensity Discharge Lights
High intensity discharge bulbs cost more than most lights, but they convert electrical energy to light more efficiently than incandescent and fluorescent bulbs. This means that using high intensity discharge bulbs in your indoor gardening setups will save you money on electricity, offsetting the price of the bulbs.
High intensity discharge bulbs are also smaller than traditional tube-shaped fluorescent lights, and about the same size as incandescent and compact fluorescent bulbs. Their small size, coupled with their high energy efficiency, allows you to provide your indoor gardens with ample lighting without your lighting system taking up much space.
There are several different types of high intensity discharge bulbs. The ones that you should use for growing plants are metal halide and high pressure sodium. High pressure sodium lamps last longer and convert energy more efficiently than metal halide lamps, but both types of lighting are necessary for growing plants. Metal halide lamps emit a cool blue light, while high pressure sodium lamps emit a warm red light. Some plants thrive best under cool lights, while others do better in warm lights, and some require different lighting mixtures throughout their life-cycle. To help your plants achieve optimal growth, consult a growing manual for the plant. These manuals should provide lighting recommendations.
In general, cool lights work best for small, leafy plants, and warm lights work best for big, flowery plants. Nearly all plants benefit from cool lighting during the early stages of their growth. Under warm lights, the growth of a young plant can be stunted. Many plants that need warm lights to grow as they mature will continue to benefit from some cool lighting. Create a mixture of warm and cool light by using some metal halide lamps and some high pressure sodium lamps. Alternate lamp types when installing your lighting so that the light will be evenly spread across the grow area.
If your plants require additional lighting, but you have run out of room in your growing area to add more lamps, consider surrounding the grow area with reflective material such as foil. This will reflect additional light onto your plants which would otherwise have been absorbed by non-reflective surfaces.