Indoor grow operations need light, plain and simple, but there isn’t a single light that is ideal for every grower, and lighting efficiency is a major factor in any grow. It’s difficult to have too much of a good thing here, but it’s certainly possible, and buying the wrong lights can be a costly mistake.
To keep that from happening, we’re going to go a little further in depth on the different factors of lighting choice, with the goal of getting a good grounding on what to look for in a light. When we’re done, you may have some work ahead of you still, but you’ll know some of the pitfalls to watch out for.
First things first, we want to keep firmly in mind what we want out of our lights. They should be producing light which our plants can use, they should be producing it in sufficient quantity to make for optimum growth, and they should do it cost-effectively.
Let There be Light
You might think that light is light is light, but we’re talking about one of the basic building blocks of physics here, so it’s not quite that simple. There are large biological differences between how we see light, and how plants absorb it.
Although both plants and humans react mostly to light in the visible spectrum (between ultraviolet and infrared), most eyes are set up to perceive the visible spectrum in a bell curve. As a result, we perceive green light much more clearly than we see red or blue light. If you’ve ever wondered why night vision goggles are green, that’s the reason why.
Plants are capable of getting more use out of the red and blue ends of the spectrum for photosynthesis than we are at seeing with those spectra. Just as light which the human eye can use has a special name: visible light, light which plants can use has its own designation, namely photosynthetic active radiation, or PAR. So PAR = visible light for plants.
To get something with units that we can use, we have to measure the amount of PAR that a fixture produces. This is known as PPF or photosynthetic photon flux. PPF is measured in micromoles per second (mol/s), where each micromole is more than 600 quadrillion photons. It tells us how many bits of light that our plants can use are coming out of a fixture every second.
Now we know how much light is coming out of a particular fixture, but we don’t know how much of the light is going to hit our plants. That depends on where the fixture is designed to focus the light, how reflective our growing space is, and where our lights are positioned relative to our plants.
Fortunately, while changes to any of these variables can change the end result, it’s possible to get a good idea of what’s happening at the plant by measuring the PPFD, or photosynthetic photon flux density. PPFD is commonly measured in micromoles per square meter per second (mol/m2/s), and readings can be taken with a quantum sensor.
Quantum sensors can cost hundreds of dollars, so many growers rely on manufacturer-provided PPFD specs, but care must be taken, as its fairly easy for this data to be skewed. In order to be meaningful, PPFD measurements should include the distance between the light source and the measuring area, how many measurements were taken, and the average of those measurements, as well as the minimum and maximum measurements.
Travis Williams is the VP of Marketing at Fluence Bioengineering in Austin, Texas, and he says that while it’s possible to estimate how much light you’re getting with conversion formulas, it’s not recommended. “Foot-candles, lux, and lumens measure light on a different curve to human vision, instead of PAR,” he said. “The number you get isn’t exact; it’s an estimate.” Fluence makes LED grow lights, and they find that growers have some common myths about lights which need to be corrected.
If the PPFD measurements check out, then we can measure the efficiency of a light by comparing its PPF to its wattage. Dividing a light’s PPF by its wattage is dividing a number in micromoles per second by a number in joules per second, giving us a ratio of micromoles per joule (mol/J). That makes sense, given that we’re trying to find how much usable light we’re getting for the amount of electricity pumped in.
For most of us, PPF and PFFD are unfamiliar measurements, and it takes a while to understand what they mean in context, but Williams says the ranges can be pretty wide. “If you’re propagating a cutting or a clone, you’re going to give the plant a much lower light intensity than when it’s fully developed. We see ranges for cuttings from 30 PPFD to 150 PPFD,” he said.
In the vegetative stage, the rule is generally the more light the better, although it is possible to have too much of a good thing. When a plant gets too much light, the top leaves are bleached white, and the plant stops growing. Too much light can also cause nutrient problems, or even heat stress if the setup’s environmental controls aren’t enough to wick away the waste heat from the lights.
Though the flowering stage is triggered by a period of darkness, cannabis plants can actually take more light when flowering than when growing. According to Williams, their growing facilities have hit up to 1,300 PPFD with no ill effects. In this final stage, because the plant is currently growing the active cannabinoids that make the plant unique, the lighting is particularly pivotal.
The current thinking is that a large variety of environmental factors, including light, play into which cannabinoids are generated in what quantities. “You can take the same plant, give it the same light intensity and spectrum, but if you change the temperature, or the CO2 or the nutrient mix, you’re going to get a different output,” explained Williams.
Just the spectrum of a fixture can affect root development, shoot development, the spacing between shoots and the ratios of THC and CBD. This is one of the current frontiers of cannabis research, so very little is known with any certainty about what a particular choice will have, giving growers almost no hard data to work from.
On the other hand, this also means that there is a lot of opportunity for growers to build and fine-tune their technique. Not only can a grower cultivate their own strain, they can take an existing strain and tweak it with their own growing techniques.
This is why consistency, in general growing practices as well as lighting techniques, is so important for cannabusinesses. Many cannabis consumers are experimenting, through micro-dosing and trying out different strains, to nail down certain specific desired effects. They need predictable effects to learn about their reactions, so they need a consistent supply.
This is one the difficulties unique to cultivating cannabis, made all the more stark because some cannabis consumers are patients looking for medicine. If a farmer grows an ear of corn a little differently, it won’t result in them being any less fed. However, a cannabis bud harvested at the wrong time, or grown under the wrong light, might not achieve the desired level of THC-V required for inducing drowsiness.
According to Eric Eisele, CEO of Growflux LLC in Philadelphia, Pennsylvania, there’s another factor to consistent lighting that you may not be aware of. “All lights degrade slowly over time,” he said. “Even in LEDs, after 50,000 hours of runtime, it’s at 70 percent brightness. So if you’re trying to get consistent qualities out of your cannabis year after year, you have to account for the dimming of your lights.”
With consistency being this important, many growers choose to implement an automated system for all or part of their environmental controls. Computer controls can go a long way to minimizing the factor of human error, and even something as simple as a timer hooked into the lighting can prevent crop disasters.
That said, anytime you make a change to your growing setup, it pays to go carefully and double-check everything. A little extra fretting may end up saving you thousands if you catch a mistake before it becomes a catastrophe.
How can lighting be so pivotal? Because from the pre-flowering stage on, cannabis plants are extremely sensitive to light, and any amount of it can disrupt the flowering process. We’re tripping a genetic switch in the plants to get them to flower on our schedule, rather than nature’s. However, even lights that are far too weak for the plants to survive on can be strong enough to flip them back.
If this happens, the plants can revert to the vegetative stage, throwing your schedule into disarray. Worse, it can cause the plants to turn hermaphroditic, growing male reproductive organs in a last-ditch attempt to propagate. These plants will have to be removed, or even trashed, discarding months of effort thanks to a single mistake.
But really, what light do I choose?
You may have noticed we haven’t talked about the different types of fixtures in this article yet, and that’s by design. There are a lot of different light options out there, depending on how large of an initial investment you’re willing to make, in both money and research. Knowing the qualities you’re looking for can help you cut through the marketing and find out what you need to know.
That said, the lighting options start out on the most accessible end with fluorescent lighting. Fluorescent gives a good spectrum for promoting vegetative growth, and with enough of them, it’s possible to grow short plants. It’s also a mature technology with a lot of backing, but there are a number of reasons why they are not generally preferred among commercial growers.
First, fluorescent lights are less efficient than other common lighting options like metal-halide or high-pressure sodium bulbs. Second, fluorescent carries extra costs. “What you’re going to find among commercial growers,” said Eisele, “is that the maintenance, labor, and disposal costs are significantly higher for fluorescent because those bulbs contain mercury.”
Kevin Frender, CTO of Black Dog LED in Melbourne, Florida, explained that they’re still in use among some because they work and they have a low start-up cost. “If people paid attention to their power bill, and saw how much they were paying for them over time, though,” Frender said, “No one would use them.”
The next step up from fluorescent in terms of efficiency is a type of high-intensity discharge (HID) light, the metal halide (MH) bulb. MH bulbs put out about half as many photons per watt as the other commonly used HID light, the high-pressure sodium (HPS) bulb. Yet, many growers use MH lights for the vegetative stage of the plant’s life cycle, and HPS bulbs for flowering and pre-flowering.
This is because HPS lights have a peculiarity to their spectrum that causes problems in vegetative cannabis. “HPS lights trigger a hormonal response in the plants, and make them think they’re being shaded out, even if you’re giving them more light than they would naturally find outdoors,” said Frender.
The cannabis plant tries to reach past the competition and get out of the endless shade and focuses on extending stems rather than growing leaves, resulting in a weak, ‘leggy’ plant. Leggy cannabis takes up growing space that is often limited (especially vertically) and can even be weak enough that the stem will snap under the weight of the bud.
HPS is, however, among the most efficient lighting methods out there, and can produce large quantities of light in a spectrum that supports flowering. The only issue with a two-light setup is that the switchover can induce shock in the plant because the sun doesn’t drastically change its light output from one week to the next. Shock will slow down the flowering process and result in lower yields, but in most setups, it’s a necessary evil.
One way of getting around this is using a ceramic metal halide (CMH) lamp. CMH is comparable in efficiency to HPS, and produces a broad spectrum, meaning it can be used for both vegetative and flowering growth. The downside is that they run three times as hot, around 1,500 degrees Fahrenheit.
That’s a pretty significant downside, not just because it poses a temperature control problem, but because the heat is hard on the lamp itself, shortening its lifespan. “CMH bulbs are limited to 315 watts or less,” said Frender. “So you have to buy three light fixtures to equal a single 1,000-watt HPS. You’re getting slightly more light out of it, but you’ve got three bulbs to change, and they run significantly hotter.”
The final group of lights that get regularly considered, if not used, for growing cannabis is Light Emitting Diodes, or LEDs. LEDs have a lousy reputation within the industry, and for good reason.
LEDs have been a pipe dream for a lot of growers because they promise so much. They get more efficient as they are cooled, they can last for years at a stretch, and produce light in a wide variety of spectra. However, while it is easy to make a cheap, crummy LED, it’s very difficult to make a quality fixture that will deliver on those promises.
The market has been flooded with cheap knock-offs, and the growers that haven’t experienced the let-down of a cheap LED have heard about it from someone who has. While there are good, high-quality fixtures out there, you’ll have to do a lot of homework to sift the wheat from the chaff. You should also expect to pay a serious chunk of change up front to get a light that will last you multiple years.
There are a lot of lights, made by a lot of lighting companies out there. This is a good thing because the home-grower fine-tuning their personal supply has very different needs from the CEO opening up their third warehouse. So call up the manufacturer, ask nosy questions, and run the numbers for yourself. You may find that the process of discovery and analysis can be just as rewarding as flipping the switch for the first time.