Best Lighting Types and Intensities for Marijuana Plant

Lumen

A unit of measurement of the total flow of light which is emitted continually from a source. One lumen is equal to the flow of light which is emitted from a very small wax candle.
The common 40 Watt incandescent bulb emits some 400 lm (lumen). So the efficiency of that bulb is 400lm/40Watt= 10 lm/watt.

LUX

= lm/m2, the intensity of light which falls on a surface.

Colour Temperature

- measured in degrees Kelvin, the color of a light’s output in relationship to the degree of heat applied to produce the specified colour of light. Daylight is measured around 5000 degrees kelvin

If we direct all light from our 40 Watt lamp towards a floor area of 1 square meter the intensity of light on that area will be 400 lux, (400 lumen distributed over 1 square meter, 400/1 lm/m2 = 400 lux,) which is a little better than moonlight, but far away from the sunlight intensities we need for growing plants.

The sun gives some 50 000 lm/m2 = 50 000 lux at the earth surface on a clear summerday. See the table below.

The 40 Watt incandescent lamp is not only too weak for growing plants, it also has too little blue in its spectrum and is far too inefficient. Fluoroscent tubes and HPS and MH lamps are the better choices.

Cannabis needs 24 hours of strong light for the first 4-6 weeks of vegetative growth. Then it needs 2 months of 12/12 hours of strong light and very dark, to flower and ripen. If they get less than 30000 lux they will still grow vegetatively but slower. And they will flower less, if at all.

Plants need 25000-50000 lux too grow fast.

90000 lux Max. Sunlight Intensity on Earth’s surface. This is too much light, it is not good for the plant.

Plants subject to intensities at this level or greater are at risk of “solarization,” whereby photosynthesis is retarded. This can happen at noon on a clear Tropical summer day, especially at high altitudes.

140000 lux Sunlight above atmosphere (Solar Constant)

More advanced theory: Scientific, but has many answers about how and why.

Air Temperatures between 23C (70F) and 32C (90F) are ideal for growth; beyond 35C (95F) can adversely affect plants, retarding photosynthesis, and, in extreme cases, can cause leaf burn if a radiant heat source is nearby.

Calculating with lumen, lux and efficiency:

The cheapest and easiest solution to the beginner is to use fluoroscent tubes. The usual ones are 120 cm (48″) long, and give at best 4000 lumen.

*****Ed Note: If you care to get a light meter and measure the light from various distances to your flouros, you’ll see immediately that you will want to keep the lights as close to the top of your plants as possible. *****

Your grow room must have at least these dimensions: 140 cm high (these plants get big, 180 cm is better, 120 cm long (to accomodate for the tubes), and wide enough, let’s say 60cm (2 feet). The easiest is to build an extra wall, made of silver tarpaulin or wood. This wall is placed 60 cm from a real wall, to create a space of say 200*260*60cm for use as a greenhouse or rather two. Build the wall and divide the space up into two small rooms. Make some type of opening, so you can take care of your plants later. Put in ventilation and cover all inside surfaces with al-foil using a stapler. We want the light to bounce around in there until it finds a green leaf to do its work in. As much light as possible is needed for the growth of the plants. The ventilation consists of a 12Volt fan which pushes the warm air from the green house through a plastic tube which ends outside the house to let the warm moist and odors out. Instead of a fake wall you can disguise the green house as a very big bass speaker, stereo wall, tv-stand, cupboard or whatever.

Buy the fluoros in ready-made units or do it yourself like this:

Buy the bare necessities to put up fluoros, that is reactors, lighters, tube holders, lighter holders, wire.7mm, capacitors and connectors.

Most of these devices have pushcontacts, that means you don’t have to solder or screw much, just strip off the insulation from the cable and push it in.

Put up as many tubes as possible in the ceiling of the green house. You might be able to get 6 tubes into every green house half. Every green house has a floor area of 0.60m*1.30m=0.78m2 With 6*4000 lumen you get 24000lumen. Divide by 24000lm with 0.78m2 to get 31000 lux, which is good enough.

Use hanging mounts for the tubes, they are cheapest and easiest to use. They also make it easier to pack the tubes densely in the cieling or hanging at different levels, hanging only in the thin electric cables. If you manage to get 10 tubes into the top of the green house you get 40000lm/0.78m2= 51300 lux in there.

As another example, let’s take one of the most popular hps grow bulbs:

The Son-T-Agro gives out 53000 lumen. If we use a reflector to direct all of that light towards a floor area of 2 m2 we get a light intensity on that area of 53000 lumen/2 m2, which is 26500 lumen/m2 (=lux)

We can see in table 3 above that it fits in: “25000 – 30000 lux =Max. Efficiency for Sub Tropical varieties”.

We add some daylight fluoros, 6 fluoros a 4000 lumen=24000 lumen. Divide by floor area 2 m2 to get =12000lumen/m2=12000lux

Together the hps and the fluoros give 26500+12000=38500lux in the 2 m2 big grow room. see table 3: 25000 – 50000 lux Max. Efficiency for Equatorial varieties.

This combination will draw 430Watt+6*40Watt+100Watt in the ballast units, total =530+240=770Watt of electricity.

Our total efficiency is 53 000 + 24 000 lm divided with 770 Watt, which is 77 000 lumen /770 Watt = 100 lm/Watt

At 38500 lux we have an illumination which is optimal for growth,

Illumination Chart

For example, from this chart we can see that a 600W HPS used to illuminate an area of 2.5 m2 will result in a lighting intensity of 36000 lux. Note that this presumes that a reflector is being used so that all the light is being directed towards this 2.5 m2 area.

LIGHT BULB PRODUCT LIST

Equivalences:

1 lm/m2 (lumens per square meter)

= 1 lux (lx)
= 10-4 lm/cm2
= 10-4 phot (ph)
= 0.093 lm/ft2
= 0.093 foot-candles (fc)

1 meter = 3.3 feet

1 square meter = 10.8 square feet

1 foot = 0.3 meter

3 feet = 1 yard = 0.91 meter

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