High Intensity Discharge Lights (HID) - These come in two types, the Metal Halide Grow Light (MH) and the High Pressure Sodium Grow Light (HPS)

Metal Halide - bulbs are designed for plants during their growing cycle. That is, for non-fruiting or non-blooming plants. Metal halide lighting is therefore the best HID choice for the plant's growing phase.

High Pressure Sodium Lights (HPS) - The HPS grow light is used primarily for plants that are in their blooming or fruiting phase. Modern high pressure sodium lighting can, however, be bought, which is enhanced for blue spectrum (for vegetative growth) and for red spectrum (for flowering growth). This means that they can be used throughout the entire growing process for most types of plant.

Fluorescent Grow Lights emit less light than high intensity discharge lights and although they can be used throughout the plant cycle their lack of brightness will produce small yields. The light produced tends to be softer and less damaging to tender young plants. For this reason, the fluorescent grow light is popular for seedlings and cuttings, an excellent way to establish young plants.

All of the above types of lights use some kind of a ballast system. The one most people are familiar with is the fluorescent light. This has, a small, built in, ballast. It allows the fluorescent tube to build up enough energy to strike, and excite the molecules within the tube, causing light to be given off.

Metal Halide and HPS grow lights are usually run from remote ballasts. These are external boxes containing the electronics to pre-heat and run the lamp. The ballast is connected to the lamp holder and to the mains power supply. Each ballast used is rated for the lamp wattage and so it is necessary to have different ballasts available for each of the different values of lamp to be used. HID bulbs should be replaced after 12 to 18 months of use. Although HID lamps will continue to light beyond 18 months of use, they will have lost up to 30 percent or more of their lumen output while consuming the same amount of electricity.

Think of a plant as a well-run factory that takes delivery of raw materials and manufactures the most wondrous products. Just as a factory requires a reliable energy source to turn the wheels of its machinery, plants need an energy source in order to grow.

Usually, natural sunlight is used for this important job. However, during the shorter and darker days of winter, many growers use artificial lights to increase the intensity of light or to expand the daylight length. While the sun radiates the full spectrum suitable for plant life, different types of artificial lighting are selected for specific plant varieties and optimum plant growth characteristics. Different groups of plants respond in physically different ways to various wavelengths of radiation. Light plays an extremely important role in the production of plant material. The lack of light is the main inhibiting factor in plant growth. If you reduce the light by 10 percent, you also reduce crop performance by 10 percent.

Light transmission should be your major consideration when purchasing a growing structure for a protected crop. Glass is still the preferred material for covering greenhouses because, unlike plastic films and sheeting, its light transmission ability is indefinitely maintained.

No gardener can achieve good results without adequate light. If you intend to grow indoors, avail yourself of some of the reading material that has been published on this subject. If you are having trouble growing good plants, then light is the first factor to question.

A large part of the success in growing hydroponically is planning where to place the plants. Grow plants that have similar growing requirements in the same system. Placing your system 1-2 feet away from a sunny window will give the best results for most herbs and vegetables. Even your regular house lights help the plants to grow. Make sure that all of the lights are out in your growing area during the night. Plants need to rest a minimum of 4 hours every night. If your plants start to get too tall, move the system to a spot that has more sun. Once you find a good growing area, stick to it. Plants get used to their home location. It may take some time to get used to a new place.