Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

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    Use the examples above to see the 1000-watt HP sodium offers more watts per square foot and m 2 to achieve the desired lumen output of 10,000 lumens. However, the bulb also produces a hot spot near the center of the illuminated area. Plants tend to grow into the hot spot and shade other plants.
    Although 400-watt lamps have a lower lumen-per-watt conversion, when used properly they may be more efficient than higher wattage bulbs. One 1000-watt halide produces 115,000 initial lumens and a 400-watt halide only 40,000. This means each 400-watt lamp must be located closer to the canopy of the garden to provide a similar amount of light. It also means that several different point sources sustain more even, intense light distribution.
Side Lighting
    Side lighting is generally not as efficient as lighting from above. Vertically oriented lamps without reflectors are efficient, but require plants to be oriented around the bulb. To promote growth, light must penetrate the dense foliage of a garden. The lamps are mounted where light intensity is marginal–along the walls–to provide sidelight.
    Compact fluorescent lamps are not a good choice for side lighting when using HID lamps. (See “Compact Fluorescent Lamps” for more information.)
Rotating Plants
    Rotating the plants will help ensure even distribution of light. Rotate plants every day or two by moving them one-quarter to one-half turn. Rotating promotes even growth and fully-developed foliage.
    Move plants around under the lamp so they receive the most possible light. Move smaller plants toward the center and taller plants toward the outside of the garden. Set small plants on a stand to even out the garden profile. Arrange plants in a concave shape (stadium method) under the lamp so all plants receive the same amount of light. Containers with wheels are easier to move.
    Take advantage of the different levels of light below the HID. Place seedlings and cuttings requiring low light levels on the perimeter and flowering plants needing higher light levels under bright bulbs.

Tall lanky buds are easy to grow in small containers.

Some clones grow so fast that the harvest is ready before plants shade one another.

You can really pack plants into a garden when they receive a lot of bright light.
Plant Spacing
    When light shines on a garden, the leaves near the top of plants get more intense light than the leaves at the bottom. The top leaves shade the bottom leaves and absorb light energy, making less light energy available to lower leaves. If the lower leaves do not receive enough light, they will yellow and die. Tall six-foot (1.8 m) plants take longer to grow and have higher overall yields than shorter four-foot (1.2 m) plants, but the yield of primo tops will be about the same. Due to lack of light, the taller plants have large flowers on the top three to four feet (90-120 cm) and spindly buds nearer the bottom. Tall plants tend to develop heavy flower tops whose weight the stem cannot support. These plants need to be tied up. Short plants better support the weight of the tops and have much more flower weight than leaf weight.
    At least 99 two-week-old seedlings or clones can be huddled directly under a single 400-watt HID. The young plants will need more space as they grow. If packed too closely together, plants sense the shortage of space and do not grow to their maximum potential. Leaves from one plant shade another plant’s foliage and slow overall plant growth. It is very important to space young plants just far enough apart so their leaves do not touch or touch very little. This will keep shading to a minimum and growth to a maximum. Check and alter the spacing every few days. Eight to sixteen mature females three to four months old will completely fill the space under one 1000-watt HID.
    Plants can absorb light only if it falls on their leaves. Plants must be spaced so their leaves do not overlap too much. Yield increases very little when plants are crowded. Plants also stretch for light, which makes less efficient use of intense light.
    Best number of plants per square foot or m 2 is often a matter of experimenting to find the magic number for your garden. In general, each 40-inch-square (m 2 ) space will hold from 16 to 32 plants.

Reflective Hoods
    Some reflective hoods reflect light more evenly than others. A reflector that distributes light evenly-with no hot spots–can be placed closer to plants without burning them. These hoods are most