Hydroponic Marijuana Grow Lighting


Marijuana Grow Lights


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Marijuana grow lighting basics

Marijuana plants need light from the right part of the spectrum with the right amount of intensity to encourage proper yet fast growth. Cannabis plants respond principally to light from the blue end of the spectrum for vegetative growth and from the red end for root growth and flowering.

The image above outlines the entire spectrum of light. Point (A) in the blue spectrum is the light source that cannabis plants require for vegetative growth and (B) outlines the red spectrum which is required for pre-flowering and flowering.

Marijuana will use the light from 400 through to 700 nanometres (nm) which will cover the chlorophyll and photosynthesis production which is known as the Photosynthetically Active Range, or PAR for short.

We can see from the graphs above how different light sources hit the Kelvin scale at different places. The metal halide (MH) grow lights are at around 3,200 to 4,000 and the high pressure sodium (HPS) grow lights are at 2,200.

The more right light marijuana plants receive, the faster and stronger they will grow.

Technical lighting basics

Let’s get into the more technical side of lighting as it is useful to know what you are actually doing. There is no point in buying the wrong lights.

Candela – This is the unit of luminous intensity with one candela.

Foot-candle – The Imperial measure of how intense your light is ie how much light is received by 1 square foot of any surface situated 1 foot from the light source of 1 candle.

Lux – The metric unit of measure for luminance of a surface. Therefore one lux is = to one lumen per sq meter or 0.0929 foot-candles.

Lumen – This is the unit of light flow which is also known as luminous flux. All lights
can be measured to a total lumen output. Light fixtures can be expressed in lumens and usually the lamp will lose intensity (lumens) as it gets older.

Efficacy of a light source – This measure lets us know just how efficient a light source is and is simple maths to work out. Total light output divided by the power input (Watts) = lumens per Watt.

Timing of marijuana grow lighting

Vegetative growth timing – This is called ‘photoperiod’ and it is the direct relationship that your plants have with the hours of light and darkness offered to them. With control over the amount of light your plants receive you can effectively dictate their grow cycle. You can replicate vegetative growth by using a timer to have your lights on between 18 and 24 hours and off with darkness for the remaining period; between 6 and 0 hours every day. More information on pruning during vegetative growth.

Induce marijuana flowering timing – In their natural environment plants begin to flower as the days shorten at the end of summer. To induce flowering you will then switch the light cycle to 12 hours of light and 12 hours of darkness for everyday. When you do this is up to you. It is sometimes considered to be more productive to force plants to flower when they are quite small (around 60 cm or 2ft.). By doing this you will be able to fit more plants under your lamp (the Dutch concept know as ‘Sea of Green’). If you are limited in the amount of seed or viable cuttings that you have you may wish to wait until the plants are bigger so that you get more buds per individual plant. Once you have induced flowering you will see changes in your plant within one to two weeks. More information on marijuana flowering.

You can also start the vegetative phase with a fluorescent light turned on for 18 to 24 hours a day for the first one or two weeks or longer. You can use a standard 48 inch fluorescent fixture (with two) 40 watt bulbs placed about 2 to 8 inches above the tops of the plants. 3 to 5 inches is ideal, but you might have to raise the light a bit higher so all the plants get some light, depending on your setup. Mix your hydroponic nutrient solution to 50% of the normal recommended strength for the first two weeks of growth regardless of lighting.

The reason for starting off with fluorescent lighting is to not give the plants too much light at the beginning of the growing process. Let them build up to it as they would in nature where the seeds would germinate in spring when the sun is not as strong as it will be in summer.

An alternative to growing under HPS or MH during vegetation is to set up a vegetative area, and a flowering area. The vegetative area would use a cloner or something similar that would allow seeds or clones to grow and two standard 48 inch fluorescent tubes, turned on 24 hours a day.

The flowering area would use a standard hydroponic set up with HPS and /or MH fixtures turned on for 12 hours a day.

While the flowering plants are going through their cycle with the hydroponic set up, the germinated seeds or clones will have a few months to develop in the cloner. After the flowering plants have been harvested, the plants in the vegetative area are ready to move to the flowering area. New seedlings or clones can then be started in the cloner.

There are two main benefits to this kind of set up. Electricity use will be about 25% to 35% less because the MH or HPS light is only on 12 hours a day. The longer a plant has been growing in the vegetative phase, the quicker it will flower.

The only drawback I have found is the extra area needed to set up two different grow areas. Since the flowering plants need absolute darkness during the dark phase, the light from the vegetative area can’t reach the flowering plants. So they need to be isolated, either by using curtains (or something similar) or by being located away from each other. More on grow lighting and vegetative growth .

Types of grow lights

Growing your plants indoors means that you will be in charge of meeting all their light requirements. There are a variety of artificial lights on the market and they all work well, albeit to different degrees.

You can run

1) Either MH or HPS light through both stages of growth (good);

2) Run a MH light through the vegetative phase of growth followed by HPS light through flowering (very good);

3) Run both MH and HPS light through all phases of growth (best).

I’ve found either a single metal halide (MH grow light) or high pressure sodium (HPS grow light) system works nearly as good as a dual system. So if you only have one or the other don’t worry, it will work just fine.

You can’t use a standard HPS bulb in a MH fixture, but you can use a MH bulb in a HPS fixture of the same wattage. I didn’t think this was possible till several years ago. So I decided to try using a 400 watt MH bulb in a 400 watt HPS fixture. The plants are growing as well as they did under the MH bulb in a MH fixture. The bulb hasn’t had to be replaced and the ballast runs as cool as it does with a HPS bulb.

So if you can only afford or only want a single fixture, I recommend getting a HPS fixture and standard MH and HPS bulbs rated for the same wattage as your light fixture. Use the MH bulb for vegetative growth and the HPS for flowering. There are HPS bulbs that can be used in a MH fixture and vice-versa. But these are special bulbs and cost about double the price of a standard bulb.

Bear in mind, you can only use a bulb of the wattage your light system was designed for. A 400 watt system only uses 400 watt bulbs. Don’t use any other wattage than the one listed on the ballast of your light system. One exception I have seen is a 430 watt bulb designed for a 400 watt system, but don’t push it further.

There will also be a lamp type specified on your light system (probably on the ballast itself). My 400 watt metal halide setup specifies an M59/H33 lamp type. M59/H33 is an ANSI (American National Standards Institute) ballast rating. M59 is a 400 watt metal halide ballast. H33 is a 400 watt mercury vapor ballast. So my light fixture 400 watts is about the best size of light for growing hydroponic marijuana in a personal garden. You should be able to grow 4 to 12 plants at a time. 250 watts should be good enough for up to about 2 to 6 plants the more Watts the more plants you can grow.

I use a 400 watt metal halide gym type light (high bay) on an 10 plant garden, it works fine with 6 to 10 plants. I usually grow 3 to 6 medium size plants at a time. I start the flowering phase at about 12 inches and the plant grows to about 18 inches at harvest time.

If you can afford a lighting system made for horticultural purposes with a good reflector and ballast, get it. It will last longer, allow the light to cover a larger area (more plants), and increase the amount of light individual plants get.

You can also find some high-end dual (HPS and MH) fixtures. These dual systems can provide both MH and HPS light through both growth phases. You might want to consider one of these, if you haven’t already bought your lighting source yet. If you can’t afford better, a high-bay or low-bay type light will work fine. I use one.

HID (High Intensity Discharge) marijuana lighting

HID lighting is the most efficient way to convert electricity into light that is available to the consumer. There are two types of HID grow lights used for horticultural lighting, Metal Halide (MH) and High Pressure Sodium (HPS). More detail on HID grow lights.

Metal halide (MH) grow lights

Metal halide bulbs produce an abundance of light in the blue spectrum. This color of light promotes plant growth and is excellent for green leafy growth and keeping plants compact. It is the best type of light to be used as a primary light source (if no or little natural sunlight is available). More detail on MH grow lights

High pressure sodium (HPS) grow lights

High pressure sodium bulbs emit an orange-red glow and are deficient in the blue spectrum. This band of light triggers hormones in plants to increase flowering/ budding in plants. They are the best lights available for secondary or supplemental lighting (used in conjunction with natural sunlight). Using this as a sole point of light is only recommend for greenhouse growing applications. More detail on HPS grow lights

Fluorescent grow lights

This type of light is perfect for starts and seedlings. They are also popular for growing low-light plants like herbs and African violets. Fluorescent lights are low intensity and need to be placed within 8” (up to 15” for shade loving plants) of the plants to be effective. They are a poor light source for flowering and budding primarily because of their low lumen output. Read about the new CFL grow lights

LED grow lights

LED grow lights (light emitting diode) are the new breed and have scientists working around the clock to make them brighter and cheaper using the optimum spectrums. LED grow lights are already the coolest method of growing and they also last approximately six times longer than any HID grow light.

Most LED grow lights range from 3W to 30W so are far less hungry on electricity when compared to the equivalent 400W or 1,000W HID. Compared to old school HID’s you will lower your power bill and have less problems with heat. You will save space as you can do away with the ballast and big reflectors. LED grow lights are an excellent idea for the small, discreet grow room. Read more detail about LED grow lights.

Incandescent marijuana lighting

These lights are also good for starting germination and seedlings and provide an inexpensive alternative to HID lights, because they do not require a ballast. These lights are only good for individual plants or small groups of plants because of their low lumen output and limited range.

Hanging height of HIDs

Due to the heat that is emitted from these intense types of fixtures, you should hang them according to size. Smaller wattage systems (100 W and 250 W) should be hung about 2 to 3 feet from the top of the plants. Medium wattage systems (400 W and 600 W) should be hung around 4 feet from the top of the plants. High wattage systems (1000 W and up) should be placed at least 4 to 6 feet from the plant tops.

The cost to run a marijuana lighting system

To get the operating cost per hour for a light, take the grow lights combined wattage, and divide it by 1,000 to get the kilowatts used. Then multiply that number by the amount your electric company charges per kilowatt hour. HID lights will use the number of watts it emits per hour, i.e.; 600w system will use 600 watts per hour (regardless of spectrum) and that is 0.6 kilowatts. So if your electric company charges you $0.10 per kilowatt hour this lap will cost 0.6 X $0.10 = $0.06 per hour to run. Multiply that out for a daily or monthly cost per lamp.

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