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Greenhouse Lighting

A greenhouse should receive natural sunlight during the year. Most plants require more than eight hours of sun a day to grow and be productive. The tropics being nearer the equator, days remain at about 12 hours a day, so plants can grow year round, and no supplemental light is needed to grow plants.

However, in the higher temperate latitudes, the days in the summer are longer (15 hours), and the winters have shorter day hours (8 hours). In the winter time, even when protected from extreme temperatures, the plants do not see enough light to grow, or they will grow very slowly.

To continue to grow plants in the wintertime, supplemental lighting may be needed. In a daylength of 8 hourse, an extra four hours of light will increase plant growth.

There are additional reasons to use supplemental lighting, including providing an adequate lighting period to allow some plants to bloom, or change growth state.

Natural Sunlight

Whenever possible, use natural light. It is free, and the plants have been adapted to sunlight, or full sprectrum lighting. Artifical light has a spectrum which is limited in some way.

Another reason to use natural light is cost. Effective supplemental lighting can be expensive to purchase and operate. A greenhouse that has access to natural light will be much less expensive to operate, if lighting is required.

Supplemental Lighting

    There are several types of lighting that can be used in the greenhouse.

Incandescent lamps - Available in sizes from 10 to 500 watts. The common household lighting is not usually used in a greenhouse. They emit excess heat, and have a poor light quality for plants. They are also very inefficient, converting only 7% of energy to light. They are, however, used to create conditions of a light period for plants with special lighting requirments.

Flourescent Lamps - Recommended for setting close to starts and seedlings. The light is hung approximately one foot above the seedling. Fluorescent lights are inexpensive to operate, and very inexpensive to purchase. They are not recommended for production growth and flowering. Fluorescents have a low output of light energy (called lumen or lux). If fluorescent lights are used as supplemental lighting in a greenhouse there will some help for plants such as lettuce and some herbs, bot overall will not increase growth very much.

Metal Halide - These lamps emphasize the blue / green spectrum to promote vegetative growth. If you have little or no sunlight available these are the systems to use. MS lamps contain a 30% boost over standard Metal Halide lamps in the red/orange spectrum and more lumens per watt than standard Metal Halide lamps. The Super Son Agro (Daylight) bulb is very high in blue spectrum and also high in red/yellow. This makes it an excellent light source for propagation and for supplementing HPS lamps.

High-Pressure Sodium - These lamps are primarily red/yellow in spectrum. These are the best lamps available for use in conjunction with natural sunlight. High-Pressure Sodium lamps promote budding and flowering in plants. The Son Agro lamps emit 30% more blue spectrum than standard High-Pressure Sodium lamps, thereby reducing inter-nodular elongation of plants. Son Agro lamps are the choice for most professional growers because they are very efficient and contain a balanced spectrum for all stages of growth.

Chart of lighting systems: coverage, cost per day etc.

The high intensity discharge lamps require a ballast, a special device hooked to the light to and they are expensive.

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