Intensity

High intensity discharge lamps are bright-very, very bright. Growers who properly manage this intense brightness harvest more weed per watt. Intensity is the magnitude of light energy per unit

TIk Inverse Square Law dictates light intensity in relation to distance.

TIk Inverse Square Law dictates light intensity in relation to distance.

This 'Chronic' cola received plenty af bright PAR watts. It developed super-thick, dense, heavy buds.

Tie ci string 12 to 36 inches long to the HID reflector. Use the string to measure the distance between the bulb and plant canopy.

Leaves reach for the light. Strong, well-illuminated plants orient foliage to catch the maximum amount of light possible, of area. It is greatest near the bulb and diminishes rapidly as it moves away from the source.

For example, plants that are two feel from a lamp receive one-fourth the amount of light received by plants one foot away! An HID that emits 100,000 lumens produces a paltry 25,000 lumens two feet (60 cm) away. A 1000-watt HID that emits 100,000 initial lumens yields 11,111 lumens three feet (90 cm) away. Couple this

Tie ci string 12 to 36 inches long to the HID reflector. Use the string to measure the distance between the bulb and plant canopy.

Leaves reach for the light. Strong, well-illuminated plants orient foliage to catch the maximum amount of light possible,

This 'Chronic' cola received plenty af bright PAR watts. It developed super-thick, dense, heavy buds.

Loose buds like this form when they do not receive enough light.

meager sum with a poorly designed reflective hood, and beautiful buds suffer big time! The closer marijuana is to a light source, the more PAR watts it receives and the better it grows, as long as it is not so close that heat from the lamp burns foliage.

The Inverse Square Law

The relationship between light emitted from a point source (bulb) and distance are defined by the inverse square law. This law affirms that the intensity of light changes in inverse proportion to the square of the distance.

Intensity = light output/distance''

For example:

= light output/distance*'

100,000= 100,000/1 25,000= 100,000/4 11,111 = 100,000/9 6250= 100,000/16

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A 1000-watt standard metal halide emits from 80,000 to 110,000 initial lumens and 65,000 to 88,000 average (mean) lumens, One lumen is equal to the amount of light emitted by one candle that falls on one square foot of surface one foot away. Super halides emit 115,000 initial lumens and 92,000 mean lumens. A 1000-watt HP sodium emits 140,000 initial lumens, and a 600-watt HP sodium emits 90,000; watt for watt, that's seven percent more lumens than the 1000-watt HPS, Lumens emitted are only part of the equation. Lumens received by the plant are much more important.

Lumens received are measured in watts-per-square-foot or in foot-candles (fc). One foot-can-die equals the amount of light that falls on one square foot of surface located one foot away from one candle.

Watts-per-square-foot (or nV) is easy to calculate, but is an erroneous way to determine usable light for a garden. It measures how many watts are available from a light source in an area. For example, a 400-watt incandescent bulb

250w

400w

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2000-3500

1900 - 2600

5400-9000

5400 - 7200

9000-12000

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800-1500

1200 - 1700

2200-4300

3300 - 4800

5 500-8000

•Min»

350-700

300 - 600

1000-2000

900 - 2400

2500-4000

1 ..'in

100 - 200

450-800

300 - 720

1500-2000

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A 175-watl HID yields enough light to grow a 2 x 2-foot garden well. Notice how fast light intensity diminishes more than a foot from the bulb.

A 250-watt HID will illuminate up to a 3-foot square area. Keep the bulb from 12 to IS inches above plants. A 400-watt HID delivers plenty of light to illuminate o'l» 4-foot area well. Hang the lamp from 12 to 24 inches above the canopy of the garden.

A 600-watt HP delivers enough light to illuminate o4* 4-foot area well. Hang the lamp from 18 to 24 inches above plants.

A 1000-watt HID delivers enough light to illuminate a 6 x 6-foot area well. Some reflective hoods are designed to throw light over a rectangular area. Large 1000-watt I lily's can burn foliage if located closer than 24 inches from plants. Move HID's cJoser to plants when using a light mover.

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600w GOOw 600w

This Adjust*A-Wing spreads light evenly and plants can he placed very close to the bulb without burning.

Three 600-watt HID's actually deliver more light to plants than two 1000-watt HID's. Smaller TIID's provide three points of light and can be located closer to plants.

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

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400w

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

400w 400w

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 emits the same vwatts-per-square-foot as a 400-watt metal halide. Mounting height is not considered in watts-per-square-foot; the lamp could be mounted at any height from four to eight feet. Nor does it consider PAR watts or efficiency of the bulb.

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400w

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This Adjust*A-Wing spreads light evenly and plants can he placed very close to the bulb without burning.

Three 600-watt HID's actually deliver more light to plants than two 1000-watt HID's. Smaller TIID's provide three points of light and can be located closer to plants.

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.

Using three <100-walt bulbs can actually cover 30 to 40 percent more growing area than one i 000-watt bulb. The 400's can also be hang closer to plants.

Calculating foot-candies 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.

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 clay 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 clay long. It is the same in an indoor marijuana garden; plants that receive less light grow poorly.

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