Hydroponics is the practice of growing plants in water or without soil. This technology has been around since ancient Babylon, but only in the last few decades has the ability to grow high light-loving plants indoors under artificial lights become possible. The type of lighting you need depends on what you plan on growing. Very high light-loving plants need intense lighting like metal halides or high-pressure sodium. Lower light levels can be achieved with compact fluorescents.
Metal halide lights are excellent for vegetative growth in hydroponics. Lamps can be purchased in the daylight range that includes both the red/orange and blue light spectrum that plants need for proper photosynthesis. Lamps and ballasts are made in the range of 50 watts to 1,500 watts, but the most common types are 250 watts, 400 watts and 1,000 watts. Metal halide lamps put out anywhere from 65 lumens to 115 lumens per watt of power used.
Metal halide lamps are rated for either horizontal, vertical or universal burning position. Universal burning bulbs can be used either horizontally or vertically. Most hydroponic growers burn lamps in the horizontal position to get the maximum amount of light evenly spread over the plants.
High-pressure sodium lamps are very similar to metal halide lamps but only put out light in the red/orange spectrum. The red/orange spectrum does contribute to photosynthesis but is primarily used for flowering and reproductive growth. High-pressure sodium lights are one of the most cost-effective types of grow lights because they are cheaper to set up and are readily available. They are widely used as street lamps and outdoor home safety lighting as well.
Compact fluorescent lamps are not as efficient as metal halide and high-pressure sodium lamps per watt of energy used, but they burn much cooler and can be used for smaller spaces and lower light-loving plants. Their compact size allows you to install them in places with limited height such as shelves and low-ceiling basements. Compact fluorescent lamps come in a wide range of color spectrum from exclusively red/orange, blue/violet or full spectrum. The cost of installation is considerably less than either metal halide or high-pressure sodium.
Compact fluorescent lamps come in a wide variety of sizes from just a few watts to 150 watts. They are also manufactured in various shapes from coils, long single tubes to U-shaped tubes. The most efficient lamps are ones that are straight tubes or U-shaped because they cast the light over the widest possible area.