Light Cycle and Distance of Lights from Plants
The seed doesn't need light to germinate. The sprout does need light as soon as it breaks through the soil. Most growers turn the light on when they sow the seeds, though, to warm the soil and encourage germination. Lights may also dray the surface of the soil, especially in large pots or with VHO fixtures. If this is a problem during germination, leave the lights off until you see the first sprout breaking through the soil; or hang the lights about 18 inches above the soil, and lower them to six inches as soon as the sprouts appear.
It is important for normal development that the plants receive a regulated day/night cycle. We emphatically recommend that you use an automatic electric timer.A timer makes gardening much easier, since you don't have to turn the lights on or off each day. The plants won't suffer from irregular hours or your weekend vacations. Set the timer so that the plants get about 16 to 18 hours of light a day, and leave it on this setting until the plants are well grown (three to six months) and you decide to trigger flowering.
During the seedling and vegetative stages of growth, the plants may be subjected to light during their night period. During flowering, however, the night period must be completely dark.
The plants grow more slowly with less than 16 hours of artificial light a day, and they may flowers prematurely. Some growers leave the lights on up to 24 hours. A cycle longer than 18 hours, may increase the growth rate, especially if the plants are not saturated with light. A longer cycle is helpful in small gardens, such as under standard four-foot fixtures.
No matter what the light source, place the lights as close to the tops as possible without burning the plants. Pay no attention to the manufacturer's instructions for the distance of the plants from the lights; these instructions don't apply to a high-energy plant such as Cannabis. With standard-wattage tubes, keep the lights from two to six inches above the plant tops. With VHO tubes, allow four to eight inches. Maintain the lights at these distances throughout the life of the garden. In most cases you will have to raise the lights once or twice a week as the plants grow.
Standard fluorescents don't get hot enough to burn the plants unless they are in direct contact with leaves for several hours. VHO tubes will burn leaves before they touch them. But you do want to keep the lights as close to the plants as possible. This encourages stocky, robust growth. Incandescents and floodlights get very hot; place them at a greater distance from the plants. Test the distance by feeling for heat with your hands. Place the bulb at the distance where you begin to feel its heat. For a 75-watt incandescent lamp, this is about eight inches.
LUDACRIS.
