One of the main aspects of growing cannabis in general and in particular growing cannabis indoors in a hydroponic manner is lighting. While outside, the sun takes care of everything, and the only concern of the grower is to find a decent spot, inside things get complicated with exactly what lights to use, over to how much light hours should the grower expose the plants, and finally what kind of light should be used, as well as as an extra the distance to the plants. All these are crucial variables in growing cannabis indoors and may play a key role in the success or failure of an indoors crop.
To start off by defining basic terms, one such key term is HID, or High Intensity Discharge lighting. This is considered the most efficient way to convert electricity into light currently available to the customer. For cannabis (or general horticultural) growing, we may consider two main types of HID grow lights in use.
MH (Metal Halide) lamps produce a considerable amount of light in the blue spectrum. The blue spectrum, along with the violet and green bands, is considered to be within 400 to 520 nm range. This range is characterized by peak absorption of the light by chlorophyll (the green pigment on the plant), creating a strong influence on the chemical process of photosynthesis. It is therefore particularly suitable for vegetative growth, making MH light bulbs the best type of source (besides the Sun) to be used as primary source of light, in case there is no direct sunlight.
A MH light bulb an the average lifespan of about 10,000 hours, translating to around 625 days of light if we calculate 16 hours a day. The bulb can be used even after the 10,000 hours mark, but light will be weaker, and it is generally recommended to replace the bulb at this stage. Metal halides produce around 125 lumens per watt, while fluorescent lights around 40, and standard bulbs around 18. This makes one 400 watt MH bulb equal in its light output to 20 fluorescent 40 watt tubes.
On to HPS, or High Pressure Sodium, which are light bulbs emitting an orange-red glow. The red band is located within the 610-720 nm range, which also means large amount of absorption by the cannabis leaves (the chlorophyll). However, this light is particularly useful for flowering and budding, which makes HPS light bulbs useful in the later stage of growing cannabis. HPS bulbs may also be used during flowering outdoors as a secondary or supplemental lighting source, such as in greenhouses.
The lifespan on average of a HPS light bulb is around 18,000 hours, making them twice as economical as metal halides. After this amount of hours, the bulbs will start consuming more electricity while producing less light, making them much less economical. Generally, HPS bulbs are considered very efficient, producing up to 140 lumens per watt. The main disadvantage of the HPS bulbs are their weakness in the blue spectrum, making them much less useful for the growing stage, unless direct sunlight (which is high in the blue spectrum) is involved in the process. Using HPS bulbs for the stage of growing may cause the plants to stretch unnecessarily long, resulting in having to prune them into the desired shape and a longer growing phase.
As far as the height of hanging the lights is concerned, their size should be calculated into the equation while hanging them. Systems with smaller wattage production should be ideally hung up to 3 feet from the plants’ top, while stronger systems (400 to 600 watt) should already hang at least 4 feet above the plants, and so on. Exposing the plants too closely to too much or too intensive sunlight is known to be harmful and deterring to the growing, and may even, if completely mismanaged, kill an entire crop.
Time is a central factor in choosing how much light the plants should be exposed to. Within indoor environments, some growers may even choose to keep the plants during the growing phase to 24 hours all day lighting. In generally, around at least 16 hours has proven to be successful in most cases, when using supplemental light. Less is needed when using MH with no direct sunlight. During the flowering phase, an on-off system of 12 hours on, 12 hours off, should be used.
In addition to HPS and MH, also popular, although less efficient, in the growing scene are fluorescent lights. These are very suitable for the start of the process or the seedlings. Because of their relative low lumen output, fluorescents should generally not be used for the stage of flowering and budding. In additional, as an inexpensive alternative to HID lights, incandescent lighting may also be used during the first stage of germinating the seeds and growing the plants.
A major aspect using lights indoors, or choosing exactly what type of light to use and how long to keep it on, is the financial one. Often, the costs of electricity may deter a grower from using the lights as much as possible and thus speeding up the process of growing. As a general equation of calculating the operating cost per hour for a light, the light’s combined wattage should be taken and converted to kilowatts by dividing it by 1000. Then, this number is to be multiplied by how much an actual kilowatt hour costs with your electricity company. HID lights will generally use the numbers of watts they emit per hours, so a system emitting 600w will also use the exact same amount, regardless of its spectrum.
Once the planter arrives at the operating cost per hour by using the formula described above, the monthly operating costs may be simply calculated by multiplying the operating cost per hour with the hours used per month.
Some lighting tips while growing cannabis are, among others:
Keep a steady cycle. The plant should be exposed to sunlight every day between exactly the same hours.
Growing needs a lot more light, between 16 and 24 hours a day. Flowering needs alternating light and darkness, in more or less equal shares. Here steady cycles are particularly important.
The lamps should never actually touch the plants themselves, even if placed really closely.