Ask GroMomma – Feb 2020

by Kathy Goff


An essential element of growing is light.  Regardless if grow your cannabis indoors or outdoors, you are going to need a good source of light.  More light means more weed. In nature, plants use the sun. Light is the force which makes photosynthesis possible, converting energy into usable glucose and oxygen. 


Photosynthesis splits hydrogen from oxygen and then combines with oxygen and glucose. Glucose is the fuel of the plant, the basic building block for growing from seed to smoke. Your plants use a lot of light to produce it, and generally, more is better. 


Cannabis plants need more light in a vegetative phase and equal amounts of light and darkness during flowering cycles. Cannabis seeds are typically germinated during the spring when the hours of sunlight in a day begin to increase. A general rule of thumb for planting seeds outdoors is from February 15 to March 15.


When the days are longest, the cannabis plant has the time and energy to develop a strong structure in preparation for heavy, sticky buds. As the shorter days warn of winter, the plants will begin the flowering process so that they can reproduce and pass on their genes. 


Growers can take advantage of the way plants develop in nature. One of these techniques is called forcing.  Forcing is taking a plant that has been experiencing very long days (between 18-24 hours) and suddenly switching the light exposure to 12 hours. By imitating the change from spring to summer, this technique has the effect of causing the cannabis plant to rapidly begin the flowering cycle.


Every cannabis strain will react slightly different to various stimuli. The bottom line is that the light cycle is very important to the end product harvested. When cannabis plants receive the right amounts of light in the right cycles, the plant will thrive. A plant flowers when the ratio of light/dark is equal while they will stop flowering when the periods of darkness are interrupted by light.


There are many options for grow lights. To keep it simple, just get an LED grow light.

LED lights are more expensive, but they last much longer and offer several advantages. They are low voltage, which means less money spent on upkeep and electricity to keep them running. Coupled with this, they produce very little heat, which means you don’t need to worry about overheating your grow room.  It reduces your reliance on ventilation and fans, adding even deeper energy savings. In fact, depending on your operation, you may very well need to heat the room if you are using LED lighting.


Remember that not all LED lights are created equal!  Be sure to check your bulbs and make sure that they are high-wattage and have a high lumen value. The higher these are, the brighter your light will be. You also want to make sure that LED lights you choose have been specifically manufactured to emit light at the full spectrum of color, which your plants need for proper photosynthesis.  

A cheaper alternative to LED lights are high powered fluorescent lights (CFL) that are now specifically produced for indoor gardening.  They are available in 2 types: Blue 6400K that emit the wavelength of light needed for plant/vegetative growth, and Red 2700K that emits the right wavelength of light for flowering growth.  To produce great crops of marijuana, you’ll need both types of lights; more of the ‘blue’ wavelength for the first two months and then more ‘red’ when it comes to the flowering phase. 

Fluorescent light fixtures, particularly those using high-output (HO) T5 bulbs, are cheaper to set up, as reflector, ballast and bulbs are included in a single package.  They don’t require a cooling system because they don’t generate nearly the amount of heat the high intensity discharge (HID) setup does. The main drawback of fluorescent lights is that they are less efficient, generating about 20-30% less light per watt of electricity used, and they last about half as long as LEDs and require much more space.

In the past, most indoor marijuana gardens used high intensity discharge (HID) lamps. HID grow lights were first invented for huge scale use in public arenas and stadiums. These lights are very powerful and have been used by botanists and horticulturalists for years. The two types most commonly used were Metal Halide (MH) which produce an abundance of light in the blue spectrum promoting plant growth and High Pressure Sodium (HPS) lamps which emit an orange/red glow triggering hormones in plants to increase flowering/budding.

The problem with HID lights is that they consume a lot of electricity for output, produce high operating temperatures, produce a wider spectrum of light; much of which is not needed or used by the plants, and require a lot of space. That’s not to say that HID lights, if used properly won’t deliver great results. They most certainly will. But when you figure in the factors of cost and safety, the newly developed fluorescent grow lights as well as LED lights have clear advantages.

Good LEDs are more expensive to buy, but they are generally the most efficient, the most effective and the cheapest to run. If you don’t have the money, CFL lights are the next best choice. They’re the next most efficient to run, in terms of performance, electricity costs and bulb replacements. 

One of the really nice things about indoor growing is that you have full control over the light. You choose how the passage of night and day will occur, so you should be mindful of providing it in ideal proportions so that your plants thrive.


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