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LESSON SEVEN

Photosynthesis and Light 7-5

Lamp Placement:
When lighting your plants, the proximity of the lamp to your plants is directly related to the intensity of the light provided. The closer the lamp, the more intense the light. When you raise your lamp, the intensity is lessened. It is important not to have your lamp so close that it burns the plant leaves.

Increased light coverage can be achieved by installing a light mover that will rotate your light. You can also use reflective paint or reflective surfaces (aluminum foil, for instance) surrounding the growing area to increase light.

Types of Lights for Plant Growth

HID (High Intensity Discharge) lights are the common choice for supplemental lighting in a large space such as a greenhouse. They are the most efficient and very intense. Metal halide, mercury vapor and high pressure sodium lights are examples of high intensity discharge lights.

If you are growing in an area that has some natural light, such as in a windowsill, you can probably light it with a less intense light. Fluorescent tubes will likely provide the additional light that you need.

Fluorescent lights will also be adequate for propagation of seedlings, plant cuttings and some low-light house plants.

In a grow room without noticeable natural light, HID's are necessary to provide ample light for plant production. High Intensity Discharge lights can create an excessive amount of heat.
When using HID's, ventilation and cooling may be necessary. Vented reflector hoods are available for this purpose. Also keep in mind that HID's require high amounts of electricity and are more costly to run than most other types of lights.

Incandescent Light:

Although some supplemental light is better than none, incandescent light offers the lowest level of intensity and is generally better used as a room light than a plant light.

Specialty incandescent grow bulbs are available and will provide a better light spectrum than a standard incandescent bulb but the intensity is still limited.

Standard incandescent bulbs are high in the red spectrum but low in the blue spectrum which most plants need for vegetative growth.

Incandescent bulbs are inexpensive to initially buy but they are generally not efficient or effective for plant growth.

Fluorescent Light:
Fluorescent tubes offer a broader color spectrum and are available in a variety of kinds including bright white. cool white. warm white. plant bulbs. daylight and full spectrum. The combination of warm and cool white offer a broad light spectrum.

Fluorescent bulbs are relatively inexpensive, long-lasting and provide even, cool lighting.

The down-side to fluorescent lights is that they are low in intensity and need to be very close to the plants to be effective. Seedlings, cuttings and most house plants will benefit from fluorescent lighting.

Metal Halide Light:

Metal halide lights offer a broad spectrum with ample blue light for vegetative growth. The metal halides are more efficient than Mercury Vapor lights. which at one time. were the primary source of HID light.

Metal halides are one of the best light sources for plant growth and, if you were using only one type of light, metal halide would be the best choice.

High Pressure Sodium Light:

High pressure sodium lights are very efficient. They are long lasting and strong in the yellow- red spectrums. Their only disadvantage is that they aren't quite strong enough in the blue spectrum for vegetative development.

The high pressure sodium lights are a good choice for flowering plants. The combination of metal halide and high pressure sodium offers the broadest light spectrum and must be used in situations where no natural light is found.

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