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Artificial Light
Starting seeds and growing house plants under artificial light

Seed starting under artificial light

When starting seeds indoors and growing house plants, light, along with temperature and humidity, can be controlled and thus become a tool for producing luxuriant healthy growth. By starting your plants under these controlled conditions it is possible to get a jump start on your spring gardening.

Using fluorescent light

With fluorescent light you can give plants just the illumination they need all the time, no matter what the weather is outside.

Seeds and transplants grown under two 40-watt, 48-inch fluorescent bulbs with a reflector may receive up to 1,000 foot candles of light, depending upon their distance from the source. See chart below.

Using two 40-watt, 48-inch fluorescent bulbs
Distance from source
1 2 3 4 5 6 7 8 9 10
(foot candles)
1,000 950 750 650 560 460 430 370 360 350

Placement of light source

Keep in mind that light intensity is not the same all along the tube. The most light is right in the middle, the least at the ends. Therefore, a light-loving plant, like the geranium, can be placed on a little block if necessary to make its tip just clear the light in the middle of the tube. Start cuttings and seeds, which are satisfied with little light, right in the peat moss toward the ends of the tubes.

Fluorescent vs Incandescent light

Fluorescent bulbs produce blue, short-waved light that encourages the growth of the leaves and reproductive parts in plants. They are better for growing plants than the incandescent ones, which give out a light in which red rays predominate. The red rays are good for top growth and seed germination. Fluorescent lights are predominately blue which helps produce flowers, develop roots and deepen color of the leaves. They are cool and can't overheat plants.

Wide-spectrum fluorescent lights

Among fluorescent lights, some types are better than others for specific purposes. The Gro-Lux wide-spectrum lamp combines some of the good characteristics of incandescent lighting with the best light ranges of fluorescent bulbs and is probably the most satisfactory single light to use for foliage plants, vegetables and flowering plants.

Raising seedlings with artificial light

A combination of the standard Gro-Lux and the wide-spectrum Gro-Lux is better for raising seedlings, propagating cuttings and forcing bulbs.

Seedlings should be placed with a distance of about three inches between the tubes and the seedling tops as soon as the green sprouts have broken through the soil. As a humidity control, put a plastic curtain around shelves; just a strip of clear plastic thumb tacked to the top and bottom shelves gives plants their own little greenhouse. Plants grown in this plastic enclosure seldom need watering, and they have that shining-with-health look that goes with plenty of humidity. Open the curtain every day to give them a change of air.

Gardener's Tip:
Seedlings sprouted in light contain, after seven days, more than four times as much vitamin C as seedlings of the same age grown in darkness. Observing the light requirements of your garden produces more healthy crops.

Feeding plants under artificial light

The more nearly perfect growing conditions are, the faster plants will grow, the healthier they will be, and the more fertilizers they will need. That is another way of saying that the plants close to the lights, which are the substitutes for the sun, need more food than plants farther away. Watch for new growth; it is lighter and thinner than the old. If they are growing fast, feed them well.

Fluorescent fixtures and bulbs

The two basic types of fluorescent lamp fixtures are the industrial type, which has a built-in reflector, and the strip (or channel) type, usually used under shelves or cabinets, with a supporting background painted with flat white paint which acts as a reflector.

Maximum light reflection

The industrial type can be hung in the open, raised and lowered with adjustable chains that hook into the fixture; however, it is normally painted with glossy white paint which reflects less light than flat white. If you choose the industrial type for its flexibility of height, it would be best to remove the glossy enamel with paint remover and repaint it with flat white, in order to get the maximum light reflection.

Sizing your bulbs

Both fixtures are available in models which hold from one to four tubes and which can take various watt-size lamps. The most readily available replacement bulbs are the 40-watt (48-inch) and 72-watt (96-inch) sizes. The 40-watt size will light a growing area of 48 by 6 inches, and the 72 watt a space of 96 by 6 inches; two bulbs would double the available growing area.

Choosing the type of bulb:

The eight-foot fixtures are most often available only in slimline instant-start types.These include the preheat lamp, the rapid-start lamp and the slimline instant-start lamp. If you use the four-foot-size fixture, a preheat lamp starter is good for the sake of economy and good performance in high humidity.

Do not assume that two short bulbs will give the same light as one long one—light intensity is reduced at the ends of the tubes and more tubes naturally will have more ends! However, two shorter tubes might give greater flexibility by letting you adjust them to different heights for different growing needs.


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