Light
During the shorter and darker days of winter, many growers use artificial lights to increase the intensity of light (for photosynthesis) or to expand the daylight length. While the sun radiates the full spectrum (wavelength or color of light) 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.
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.
--Rob Smith
A number of lighting options exist for hydroponic gardeners. Two considerations must first be evaluated: What type of hydroponic system you are going to use and where are you are planning to situate it. Once you have answered those two questions, you will have significantly narrowed your options.
Some commercial and hobbyist hydroponic growers--especially in temperate or tropical regions--work outdoors. This especially makes sense in tropical areas, since they can grow outdoors all year long. Otherwise, growers simply work outside during the appropriate seasons.
Incandescent bulbs (the most common type used in the home) pass electricity through a fine filament (usually tungsten). The filament heats up, glows, and gives off heat. These bulbs are cheap and work with universal sockets. However, they do not supply a full enough spectrum to be adequate for most growing needs.
If you need to supply artificial light, you have some choices. The best option for an indoor grower with limited or no natural light is to use a high intensity discharge (HID) setup. HID lights flow electricity through vaporized gas under high pressure. The best HIDs for growing are metal halide (MH) and high-pressure sodium (HPS) lamps. One big difference between these bulb types is that MHs can be used from seed germination through bloom. Usually, HPS lamps are only used during bloom cycles. Also, MH lamps more closely resemble natural sunlight. One downside with these lamps is cost: They can be expensive (up to $300 for the ballast, base, and bulb).
One economical alternative for beginners is to use fluorescent lights. A setup of ballast, base, and bulb should only run around $20. In order to maximize results, you will need to use different bulb types during different growing cycles. Each type of fluorescent bulb puts out a different spectrum. Warm white bulbs gives off more red light, which is good for flowering. Cool white bulbs give off more blue light, which is good for vegetative growth. Fluorescent bulbs are pretty inexpensive, so you should be able to purchase both types.
Another consideration is how many lights you will need. The variables involved here are the type of plants you are growing, how many plants you are growing (usually measured in total square feet of plants), and the wattage of the bulbs you will be using. Many growing consultants and equipment merchants believe that 20-40 watts per square foot is an acceptable level of light. Remember that plants have different light requirements and needed periods of rest. Check plant requirements before shopping.
Greenhouse Growing
Some areas are blessed with enough natural sunlight year-round that growers do not need to supplement with artificial light. However, if you are growing commercially, or you don't get enough natural light, you may need to include some artificial lights in the greenhouse. These can be used on an on-demand basis, such as on cloudy days. Other greenhouses always supplement a low level of light for their plants.
Indoor Growing
For a beginning experiment in indoor hydroponics, there isn't anything wrong with simply placing your system by a sunny window. If you catch the indoor gardening bug and decide to develop a more sophisticated (or just larger) system, dedicated lighting will probably be necessary.
Further Reading