Grow Lights for Vegetative Growth

When you’re setting up your first grow there are many important factors to take into consideration if you want to get the best yield and highest quality of bud from your crop. The genetics of your seed stock or clones will play a huge factor, as will nutrient and soil blends, but one of the most important of all things is the lighting you use.

From seed germination to the growth of seedlings, new clones, vegetative stage growth and flowering, the lights you choose will help determine how vigorous, healthy and robust the growth of your plants will be. The vegetative stage of growth is one of the most important and generally lasts anywhere from 6 – 12 weeks or longer, depending on the strain you’re growing and your personal preference as a grower. Which lights you choose for this stage of growth will have a huge impact on the growth rate of your cannabis crop.

Light comes in many different wavelengths however, and cannabis uses specific wavelengths for vegetative and flowering, respectively. You may have noticed that some lights, like many fluorescents, are marketed as cool blue or cool white lights. What that means is that the light bulbs have been designed to produce light that is specifically toward the low, blue end of the light spectrum, as opposed to the red or infrared wavelengths higher up the spectrum.

During the vegetative stage of growth, cannabis uses light from across the whole spectrum, but the most useful wavelength for vegetative growth is the cool, blue light produced at the lower end of the spectrum. Some growers, especially those on a tight budget, choose compact fluorescent lights (CFLs) for the vegetative stage of their cannabis grow, but not all lights are created equal. Although you can achieve decent results with CFLs, a far better option for monstrous vegetative growth is a metal halide light.

Metal halide (MH) lights are part of a class of light bulbs known as high intensity discharge (HID) lights, and among amateur and professional growers alike they are some of the most popular lights for use during the vegetative stage of cannabis growth. MH lights produce an abundance of light at the lower, blue end of the spectrum, which is ideal for photosynthesis and the production of dense, leafy green material.

Although MH (and other HID lights) are more expensive on a one-for-one basis than CFLs and similar, low-cost lights, the biggest advantage of using a MH bulb is in the lumen output. Lumens are the measurement given to the amount of usable light produced by a bulb. A typical CFL will produce ~ 50 – 70 lumens per watt of power, so a 100 watt CFL would produce ~ 5000 – 7000 lumens of light, whereas a regular incandescent bulb only produces ~ 10 – 17 lumens per watt. A MH light produces ~ 75 – 100 lumens per watt, yielding 7,500 – 10,000 + lumens from a 100 watt bulb. The light from a MH is also stronger, making it ideal for canopy penetration, whereas CFLs are weaker, leading to poor canopy penetration.

Lumens are important to consider because cannabis is a very light-loving plant. A minimum of 3,000 lumens per square foot of grow space is recommended to achieve decent growth, but cannabis really flourishes when it receives as much as 5,000 – 10,000 lumens per square foot.

Some growers opt for CFLs due to concerns about electricity use and the heat production of a ballast and MH light. Some power companies do watch for ‘unusual spikes’ in energy consumption and may report you to the authorities as a result, but a single MH light of 250 watts or even 400 watts is unlikely to draw unwanted attention. Heat production is another matter, though. Since the MH requires a ballast for proper use, there is greater heat production with these lights. As a result, MH lights aren’t the most suitable lights for use in very small grow areas.

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