Light is one of the most important factors for optimal growth in your cannabis plants. It is also one of the least understood, with many growers wondering what kind of light they should use and how much light their plants need. In this article, we will discuss all you need to know about grow lights for indoor growing including what they are, how expensive they can be, and how best to measure them. We’ll also give you some tips on optimal lighting distances and more.
Why is light important to cannabis plants?
Light is important to any plant because it gives them the energy to grow. Plant photosynthesis happens when plants absorb light and then use that light energy as fuel for their growth process. Additionally, light is extremely important to cannabis plants because the hours of light they receive can trigger them to start their flowering stage. When it comes time for harvest, your plant’s bud should be as large as possible and covered with resin glands that give you a high THC content and cannabinoid production.
What are the different kinds of grow lights?
There are three common types of light sources used in indoor cannabis cultivation, high-intensity discharge (HID), compact fluorescent lamps (CFL), and light-emitting diode (LED). Let’s take a closer look at all three cannabis lighting systems below.
High-intensity discharge (HID)
HID grow lights were some of the most common grow lights used in cannabis cultivation. This type of light uses a large ballast, which is an electrical device that provides optimal power to your HID light bulbs. Once you have one of these bulbs connected to a compatible ballast and placed inside of a reflector hood, it’s ready for action. HID lights typically come in two forms, metal halide (MH) and high-pressure sodium lamps (HPS).
MH bulbs emit a blue light that is great for vegetative growth cycles, while an HPS bulb emits a reddish-orange light that is better for the flowering phase. These lights are relatively inexpensive but will require lots of electricity which will lead to higher costs over time due to energy consumption. They also give off lots of heat, which can be a problem in an indoor tent, and also contain heavy metals.
Compact fluorescent lamps (CFL)
CFLs are another popular type of grow light for small-scale indoor growers. These lights use a fraction of the power that an HID light uses and come in a variety of shapes and sizes. CFLs are available in both a cool and warm spectrum of light, so it’s important to get the right kind for your grow.
The downside to CFLs is that they don’t produce a lot of light and need to be placed close to your plants. During the flowering stage, growers will often need supplemental lighting to the CFLs to help the plants put on some weight during indoor cultivation. This kind of fluorescent light is what you see in most office buildings and the most common size is “T5”, where the T stands for tubular and the 5 references the 5/8 of inch circumference of the lights.
Light-emitting diode (LED)
LEDs are the newest type of grow light on the market. These lights are extremely efficient and put out more usable light than other types of grow lights, while some can remain cool to the touch. LED technology has come a long way in recent years with some companies offering full-spectrum LED lighting that is optimal for both vegetative growth and flowering stages. LEDs can be expensive but are a great long-term investment because they last a very long time and are very energy efficient.
How expensive are the different kinds of grow lights?
All three types of grow light have their own unique benefits and drawbacks, which will affect the overall cost. HID lights are typically the most affordable option but use more electricity than CFLs and LEDs. CFLs are the cheapest option to operate but don’t produce a lot of light. LEDs are the most expensive upfront but can be more efficient in the long run. It will all depend on your own preferences and financial constraints to decide what is best for you. If you are uncertain if you will like growing cannabis, it may be a good idea to try HID or CFL lights first to see if you enjoy it and then to upgrade later if necessary. If money is not a problem, this may be unnecessary.
How should I measure the intensity of my grow lights?
The brightness or intensity of your grow light is measured in several different units including Watts, Lumens, Lux, DLI, Kelvin, PPF, PPFD, and PAR.
Watts
Watts are the most common way to measure the intensity of light and are simply how much power the light consumes. The power of a light is measured in watts, if you have a small grow area, using between 400-600 watts is optimal. Lights with higher wattage are better suited to larger grow areas or if you need your light further away from the plants during vegetative phase, while smaller lights should be placed closer to your plant during flowering.
Lumens
Lumens are a measure of how bright a light appears to the human eye and are typically used when measuring indoor lighting.
Lux
Lux is another common measurement and is simply how bright the lighting appears from one meter away. Lux meters are the most common for measuring light intensity today, but they can be expensive and are not necessary unless you are trying to fine-tune your grow.
DLI
DLI refers to the daily light integral or the total amounts of light a plant receives in a day. It is measured in mol/m²/day and takes into account both the intensity and duration of light received by the plant.
Kelvin
Kelvin simply refers to the color temperature of the light this unit measures the light intensity on a color scale and is not the same as the kelvin temperature unit.
PPF and PPFD
This is PPF (photosynthetic photon flux) and PPFD (photosynthetic photon flux density) measure the number of photons a light emits per second.
PAR
PAR measures only the photosynthetically active radiation or the wavelengths of light that plants use during photosynthesis, which are 400-700 nanometer or blue, red, and far-red (infrared) wavelengths that are not visible light.
There are some apps available, such as Photone, that offer measurements in various units and can measure your light by using your smartphone. There are also converters online to convert various measurements into other ones. For example, a converter from PPF to PPFD. Light measurement instruments are also available from different companies but typically are far more expensive.
How powerful should my grow lights be?
There are no set rules on how powerful of a light you should use, but there are optimal ranges based on many different factors. It is optimal to keep your lights as close to the plants during flowering for optimal light penetration and even growth. As stated above, if you have a small grow area, so a 3 ft. by 3 ft. tent or smaller, using between 400-600 watts is optimal for quality crop production. Many lights will also have different measurements (DLI, lumen, etc.) available in their descriptions if you would like to compare them.
How close should my plants be to my lighting?
It is best to keep your marijuana plant as close to the lights as possible during any stage of growth. This means that if you have a small grow area, such as a tent, it is optimal to keep your lights at 24-30 inches above the canopy during the germination and seedling stage. For the vegetative stage, it is best to keep your lights 18-24 inches above the canopy. During the flowering stage, your light should be placed 12-24 inches from your light depending on your intensity. It should be noted that some LED lights now have dimmers for lighting control which can allow you more leeway when adjusting the height of your light by increasing or decreasing the intensity of the light. Weaker lights, such as CFLs, may also need to be closer to the canopy.
Any other tips for my grow lights?
Yes! The first tip would be to ensure your grow light has ratchet hangers. It is common practice to use these, which are ropes that use a simple pulley system, to raise or lower your lights and are very cheap to buy. The second tip is if you have an exhaust system, ensure it has a carbon filter and ducting that matches with the size of your grow room. This ensures optimal airflow for optimal plant growth during both vegetative and flowering stages.
The last tip is that if the temperature will be a problem, you may want to buy an LED light with a detachable driver. The driver is the motor that powers the light and can emit a lot of heat, even though LED lights emit less heat than their two counterparts. Some LED lights now give you the option of removing the driver from the tent so as not to unnecessarily heat the inside and make it hotter.
Summary
Light is important to any plant; however, when using artificial light it is especially important to indoor cannabis growers for plant development. There are three common kinds of lights that a cannabis grower can use today, including HIDs, CFLs, and LEDs. All have pros and cons listed above and which one is right for you will depend on your budget, space, and in some cases the light spectrum provided by the light. Light intensity is measured with various units of measurement, although there are apps available that measure in multiple units, and there are free converters online to convert one unit to another. How powerful your grow lights are will depend on the situation with your grow space and your budget. Typically, the more powerful the light the better for producing bigger yields. When growing, your lights will need to be at various heights during different stages of growth and you can easily accomplish this using ratchet hangers to hang your light.
Thank you for reading our article, should you have any further questions please see our articles regarding equipment for starting out, light burn, and temperature.
To learn more about growing cannabis at home consider checking out our guides on: Getting Started, Troubleshooting, and Optimizing your Grow or search our Knowledge Base.
We strive to help your plants thrive.
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