Sun light vs articical light
One of the main benefits of artificial light is that you can control how many hours of light per day your plants receive. This way, those living in northern or southern latitudes can provide their plants with light for growth and development even when the sun sets early, in essence tricking the plants into believing that it is summertime and that they should continue to grow rather than become dormant or, in the case of annuals, die. In addition, your plants will receive constant direct light for as long as you leave the lights turned on.
Read more: http://www.ehow.com/about_6720270_sunlight-artificial-light-plant-growth.html#ixzz2isDOMjQa Incandescent Light
Although affordable, incandescent lights provide little of the blue-spectrum light essential to plant growth. They are less efficient than other artificial lights as they produce less illumination while utilizing more energy. To draw the most benefit from an incandescent light, you would have to place it close to your plants, and because incandescent lights produce more heat than other types of bulbs, this would likely result in burning your plants. Incandescent bulbs also have very short lives. High-Intensity Discharge Light
High-intensity discharge lights produce far more illumination while using much less electricity than incandescent bulbs. In addition, while they produce a considerable amount of heat, you can hang them twice as far away from your plants as you would an incandescent bulb, so burning of the plants is less likely. High-pressure sodium lamps emit much red-spectrum light and little in the blue spectrum, making them ideal for greenhouse flowers to supplement natural sunlight and encourage blooming. Metal halide bulbs emit more blue-spectrum light, making them perfect for indoor growing operations for plants that will not flower, such as decorative plants and herbs. HPS bulbs last 12 times longer than incandescent bulbs, and MH bulbs can last five times...
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