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

foliage if located closer than 24 inches (60 cm) from plants. Move HIDs closer to plants when using a light mover.

Plants are spaced evenly in this bed of contiguous growing medium.

Each bud in this Swiss garden grows from a clone that is spaced one foot (30 cm) apart.

This Adjust-A-Wing spreads light evenly and plants can be placed very close to the bulb without burning.
    Calculating foot-candles or lux is a more accurate way to estimate the amount of light plants receive, but it still lacks the precision of measuring how much light is used by plants. If you start with a bulb that is rated in PAR watts, using a foot-candle or lux meter will suffice.
     
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    The benefits of using lower wattage bulbs include:
    More point sources of light
    More even distribution of light
    Able to place bulbs closer to garden
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Using three 400-watt bulbs can actually cover 30 to 40 percent more growing area than one 1000-watt bulb. The 400’s can also be hung closer to plants.

Three 600-watt HIDs actually deliver more light to plants than two 1000-watt HIDs. Smaller HIDs provide three points of light and can be located closer to plants.
    To demonstrate how dim light intensity retards plant development, check out an outdoor vegetable garden. Have you ever planted 65-day broccoli that took 100 days to mature? Most gardeners have suffered this fate. Did the plants get full sun all day long? The seed vendor assumes seeds were planted under perfect conditions–full sun and perfect temperature range. Plants that received less PAR light matured slowly and produced less than plants getting full sun all day long. It is the same in an indoor marijuana garden; plants that receive less light grow poorly.
Lamp Spacing
    Light intensity virtually doubles for every six inches (15 cm) closer an HID is to the canopy of a garden. When light intensity is low, plants stretch for it. Low light intensity is often caused by the lamp being too far away from plants. Dim light causes sparse foliage and spindly branches that are further apart on the stem.

Light in tensity is brightest directly under the bulb. To promote even growth, arrange plants under lamps so they receive the same intensity of light.

This gardener is able to rotate and move plants around within the garden beds. Wheels on the bed make it easy to rotate or remove entire beds.

A large bed on casters is easy to maintain.
    Increase yield by giving growing area uniform light distribution. Uneven light distribution causes strong branch tips to grow toward the intense light. Foliage in dimly lit areas is shaded when light distribution is uneven.
    Reflective hoods ultimately dictate lamp placement–distance between lamps and above the plants. Nearly all stationary lamps have bright (hot) spots that plants grow toward.
    Growers prefer high-wattage lamps–400, 600, 1000, or 1100 watts–because they have lumens-per-watt and their PAR rating is higher than smaller bulbs. Plants receive more light when the lamp is closer to the garden. Even though 400-watt lamps produce fewer lumens-per-watt than a 1000-watt bulb, when properly set up, they actually deliver more usable light to plants. The 600-watt bulb has the highest lumen-per-watt conversion (150 LPW) and can be placed closer to the canopy of the garden than 1000 or 1100-watt bulbs. When the 600-watt bulb is closer to plants, they receive more light.
    A 1000-watt HID emits a lot of light. It also radiates a lot of heat. The bulb must be farther away from the plants to avoid burning them. In many cases it is more effective to use smaller wattage bulbs. For example, two 400-watt bulbs can be placed closer to plants than one 1000-watt bulb, and the 400-watt bulbs emit light from two points. The disadvantage is that two 400-watt systems cost more than one 1000-watt system.
    Check out the diagrams that show the difference in usable light in different sized growing areas. Growers who use these drawings fine-tune the area with a hand-held light meter.
    Look at the simple mathematical examples below to see how much more efficient 400 and 600-watt lamps are than 1000-watt lamps.
    For example, a 1000-watt lamp that produces 100,000 lumens at the source produces the following:
    The goal is to give plants 10,000 lumens.
    If you use three 600-watt HP sodium lamps, you get a total of 270,000 lumens at a cost of $0.18 per hour (cost per kWh = $0.10). If you use two 1000-watt HP sodium lamps, you get a total of 280,000 lumens at a cost of $0.20 per