MARIJUANA GROW LIGHTING BASICS
Before you pick out the right grow light for your setup, there are a few basic terms to become familiar with. Every grow light is rated by the number of WATTS that is uses. This number tells you how much power, or electricity, it will take to run each grow light for an hour of use. The next term to become familiar with is LUMENS. The number of lumens determines how much light is being produced by every grow light. For example, a standard incandescent 100 Watt household bulb will produce around 1600 lumens where a 400 Watt High Pressure Sodium (HPS) grow light will put out about 50000 lumens. By dividing the number of lumens by the watts consumed, this will give you what is called the efficacy, or efficiency, of your grow light. While the 400W HPS bulb will use about 4X more power than the 100W household bulb, it can generate more than 30X the light output in lumens. This means that the HPS light is running at least 30X more efficiently than your standard incandescent lamp bulb. All bulbs will decrease in total lumen output the more they are used but this happens over many months. One aspect of lumens that is overlooked by many growers is the fact that the lumen rating of all grow lights is measured at a distance of one meter. This means the closer to your plants you can place your grow lights, the more lumens are actually reaching your plants. This can make a big difference when you consider that LED or CFL grow lights run cooler than HID grow lights, but more on that later. The term KELVINS describes the light temperature, or perhaps a better way to explain Kelvins is in terms of the light color produced. Most of the visible light spectrum runs from around 1000K – 10000K, with our focus being the 2000K – 6500K range. Flowering grow lights produce an orange color light around 2800K, while Vegetative grow lights put out a more blue/white light closer to 6000K. Knowing the Kelvin output of your grow lights is important because the different stages of plant growth require different Kelvin temperature/color lighting.
High Intensity Discharge (HID) lighting has been used in greenhouses and indoor grows for decades. The two types of HID lights are High Pressure Sodium (HPS) and Metal Halide (MH). HPS bulbs put out the most light in the red/orange/yellow light spectrum, or 2000K – 3500K range. MH grow lights produce the majority of light in the blue spectrum, or 5000K – 6500K range. HID bulbs are very energy efficient with HPS bulbs producing around 140 lumens per watt and MH bulbs usually generating 75 – 100 lumens per watt. HPS and MH lights are most often available in 70, 100, 150, 250, 400, 600, and 1000W models. The use of either MH or HPS will require a ballast to power the bulb itself, and this will add somewhat to the total electrical pull of your grow lights.
Compact Fluorescent (CFL) grow lights have become increasingly popular in recent years due to the greater efficiency and versatility of newer designs. While CFL bulbs do not produce as many lumens as there HID counterparts, they may be placed closer to your plants as they do not run as hot as the HID options. This means you will often achieve a greater lumen rating than designated by the manufacturer, something many growers overlook. CFL bulbs come in sizes from (7 – 26W), most household applications, to the (42W-200W) range used in applications such as security lighting or professional photography. Any of these bulbs can be used to grow plants with the smaller CFL bulbs primarily used for growing seedlings or clones, and larger CFL bulbs for vegetative and flowering cycles. Most CFL grow lights will be self-ballasted but some require an external ballast, very common with many outdoor lighting units. Make sure you are aware of what you are buying. CFL bulbs come in four main colors. Soft White (2700K) is best for use during the flowering cycle, while Daylight (5000K) and Cool White (6500K) are appropriate for vegetative growth and seedling/cloning applications. Full Spectrum (4200K) bulbs provide a wider range of light and are intended for use throughout the entire grow cycle. Some manufacturers will label these types differently so be sure to check the Kelvin output before selecting your lights.
Light Emitting Diodes (LED) are the newest option for marijuana growers. LED lights come in a variety of colors from blue for vegetative, to yellow, orange, and red for flowering. Broad spectrum LEDs are also available and can be used from seed to harvest. The LED option produces virtually no heat so they can be placed much closer to your plants than either HID or CFL bulbs. Since LED lights convert almost all the electricity to light, not heat, this means they run about 4X – 5X more efficiently than HID lights, saving you money on your power bill. LED grow lights do not require a reflector or ballast to operate and are available in 1W – 5W models. 1W LEDs are reported to be more reliable and longer lasting than 2W, 3W, or 5W models. LED grow lights have large clusters of individual diodes grouped together to produce the total light output so the more diodes a light contains, the more light it outputs.
Reflectors are used in conjunction with HID and CFL grow lights to better focus the light onto your plants. Aluminum is the most common material used today and most HID grow lights will include a reflector. Some larger CFL grow lights will come with a reflector but usually smaller CFL bulbs will not. If you choose to use smaller CFL bulbs, you may want to invest in a small reflector similar to the kind found in shop work lights. Grow reflectors are available in air-cooled models that have built-in 4”, 6”, or 8” round openings designed to be used with a cooling fan and ducting to draw heat away from your light and your plants. High-end models even come with sealed glass panels between the bulb and the plants to trap heat in and avoid exposure.
OPTIMAL LIGHT HEIGHT
The Optimal Light Height (OLH) of your grow lights is determined by what type of light you are using and how much heat is being generated. LED lights can be used as close as a few inches from your plants but its best to place them 12” -18” above the tops of your plants for better overall light dispersion. HPS and MH bulbs can be used as close as 6” – 12” from your plants but this is most common for smaller size (70W – 250W) bulbs only. Larger HID (400W – 1000W) bulbs need around 18” – 24” to properly and evenly distribute light as well as keep the heat produced off your crop. CFL bulbs are subject to interpretation because of the many different uses they offer. In cloning or when starting seedlings you may want lights 4” – 6” above your plants for maximum growth. In the vegetative or flowering state you generally want 12” -18” of space to provide better light coverage to all your plants. This can be different as some growers like CFL bulbs for supplementing a main HID grow light so they will place them much closer. The biggest problem with using CFL bulbs too close is your plants can grow into the bulbs and get burned from the heat. Keeping a fan and proper ventilation system running at all times will take the heat stress off your plants to some extent. Depending on what application and what light you are using, your OLH will differ greatly due to factors such as number of plants, number of lights, grow room size, reflector type, and required light penetration. For example, the Sea of Green (SOG) growing technique calls for a level, flat layer of bud sites, so deep light penetration is not an issue here and grow lights can be placed closer.
VEGETATIVE LIGHT CYCLE
The Vegetative light cycle is the first stage of growing medical marijuana. This is when your plants develop their foliage and put on size to prepare for the flowering cycle. The vegetative light cycle is used for growing clones and starting seedlings as well. The blue light spectrum is needed to encourage proper growth so using MH bulbs are the best option for HID setups. If using LED or CFL grow lights you need to be sure the light output is in the 5000K – 6500K range. Many growers strongly advocate the 6500K range because this tends to produce shorter, bushier plants versus the 5000K bulbs. The vegetative cycle requires 18 -20 hours of light every day, with 4 -6 hours of darkness, known as (18/6) and (20/4), respectively. Some growers opt for a complete 24 hour light cycle but since this means your lights never turn off, you will wear out your grow lights faster and have higher power bills. Vegetative cycles can last from only a few weeks to several months with most growers’ vegging their plants for about a month before switching to the flowering cycle.
FLOWERING LIGHT CYCLE
The Flowering light cycle is the second and final stage of your plants. During this phase the plant switches to devoting energy from producing foliage to developing the flowers that, when dried, become your medicine. Yellow, orange, and red light is optimum for proper flowering. This means HPS bulbs are ideal for HID setups and LED/CFL bulbs must produce light from 2000K – 3500K range to develop healthy buds. The most common schedule is 12 hours on and 12 hours off (12/12) every day. Some experienced growers will induce flowering with a longer light cycle like (14/10), then move to (12/12). Other growers feel that more darkness enhances bud quality and yield so they start with (12/12) and turn to (10/14) cycle late in the flowering stage, sometimes even finishing with a few days of total darkness (0/24) right before harvesting. The flowering cycle is also very important for sexing your plants. When you switch to flowering, your plants will reveal their sex as either male or female. Male plants will have small round green sacs that hang from the main stem at the points where the side branches are connecting. The females will show small white hairs protruding from tiny conical shaped sites at the same places. You may want to use a magnifying glass to help you identify the two if you are unsure about the sex. The male plants must all be removed from your grow room otherwise your females plants will become pollenated and produce inferior buds full of seeds. This must be done as soon as you identify the sexes because the males will quickly begin to pollenate and ruin your crop.
COSTS OF LIGHT SYSTEMS
The cost of your grow lights is in direct relation to the number of Watts you are consuming and the number of hours your lights are on each day. Also take into account the cost your local power company is charging per Kilo Watt Hour (kW/h). This is the cost of using 1000 Watts of electricity for one hour. To find out what you grow lights will cost each month; add up the number of hours per day your lights are on for the entire month. Next multiple the total hours by the total number of Watts your grow lights are consuming, keeping in mind that HID grow lights will require about 15 – 18% more Watts to run the ballast. You must then divide this figure by 1000 to determine how much power your lights need. The (HOURS) X (WATTS) / 1000 = (KWH) used. Most power companies in the US are charging between (.09 cents) and (.14 cents) per KWH, depending on where you live and what month it is. Some companies charge a bit less during the summer months when power usage is highest but best to check with your local provider. Finally you need to multiply the number of KWH used by the KWH rate the power company is charging you. A month of (18/6) vegetative growth using 400 Watts at (.10/KWH) is shown below.
18 hours/day X 30 days = 540 hours/month
540 hours/month X 400 Watts = 216000 Watts/month
216000 watts / 1000 = 216 KWH/month
216 KWH X (.10 cents/KWH) = $21.60 each month
Alright guys & gals!.. I hope you’ve learned a lot in this introductory!
Until next time,
Keep it GREEN, keep it LOVING and full of LIGHT.