Shining a Light on…. Grow Lighting Terminology
This blog is the first in a three-part guest series. Fohse is proud to partner with Ed Rosenthal to educate cannabis cultivators on the benefits of high intensity lighting in the grow room. Fohse has been leading the industry for the last 6+ years in making high powered LED fixtures designed specifically to grow cannabis. The promise of higher efficacy coupled with greater PAR output has lured celebrities and industry veterans alike to purchase Fohse high intensity LEDs. All are eager to increase their yields while lowering their bottom lines.
Fohse F1V @ Remedy Cultivation
Growing cannabis can be complicated. While horticultural experts have simplified the process to nine parameters that govern growth, the management of each individual parameter is still complex, as they are all intrinsically linked. Cultivators must find the perfect levels of soil/medium, nutrients, CO2, water, root temperature, ambient temperature, air velocity, humidity, oxygen... and then there’s the lights.
Light affects every aspect of a crop’s wellbeing. As the amount of light a plant gets changes, every other parameter affecting the plant needs to be altered. When light is at higher intensity, plants will absorb more nutrients and water, consume more CO2, and go through photosynthesis at a faster rate. If a light is too hot or too cool, it affects ambient temperature, root zone temperature, soil moisture and humidity. More air conditioning may be required, which in turn necessitates more air and changing the velocity of air in the room. It’s a complex system that can only really be mastered through a lot of information, plenty of trial and error, and a bit of luck.
Lighting a grow house can be a pain to figure out -- there is enough terminology to master on this one topic to fill a glossary. Some manufacturers hope you won’t know the lingo. They may throw acronyms and data points at you to make you think you’re getting a good deal.
Let’s take a look at some of the terminology surrounding lighting and shed some light on a part of the industry that has been shrouded in darkness.
Full Spectrum, Demystified
You may already be familiar with the basics of light. Light is made up of photons, tiny particles that also act as waves. We measure light by observing the distance from one peak of its wave to another, which is known as a wavelength. What we perceive as light is actually a sliver of the full electromagnetic radiation spectrum. The visible spectrum of light, what we can see, ranges from a wavelength of about 380 to about 750 nanometers.
Photosynthetically Active Radiation, or PAR, is the part of the electromagnetic radiation spectrum that is useful to plants and algae to activate photosynthesis. PAR has a similar range to the visible spectrum, from about 400 to 700 nanometers.
Claiming that a light is full spectrum is saying that it emits light at all the wavelengths within the PAR spectrum, from violet to red.
Now, all grow lights should emulate the sun as closely as they can, because all plants evolved to grow in sunlight. The best spectrum for growing plants is the spectrum of natural light emitted from the sun. However, sunlight is fickle and unpredictable, so the closest thing we can get that delivers a similar spectrum is the full spectrum LED grow-light.
Because of the tilt of the planet and the angle at which sunlight hits the Earth, the ratio of colors within the spectrum of light changes based on the season. Typically, higher-end LED fixtures like the Fohse A3i will give you the ability to change the ratio of colors within the spectrum to simulate seasons like spring, summer, and autumn. This triggers photomorphogenic responses within the plant that can encourage it to grow taller, shorter, heartier, to flower sooner or later, or to maintain its current size.
Measuring Light’s Effectiveness
Any instrument used to produce light for plants will be measured in terms of how effectively it is able to produce light within this range. Therefore, any figures on a grow light’s effectiveness will be completely useless to someone who doesn’t understand what PAR is.
In PAR, different colors produce different effects within the plant. Blue photons inhibit cell growth, which may sound bad at first, but at low levels, it can help the plant grow thicker before it flowers. Green photons penetrate leaves, bringing light through the canopy to lower parts of the plant and play a key factor in how our eyes are able to perceive plants. Red photons are great for photosynthesis but lack the green photons' penetrative ability. For plants, a combination of all colors is necessary to achieve an optimal yield. Much like humans, a plant needs a diverse range of “food” to be healthy. If there is just one type of photon, the plants suffer.
Fohse A3i @ NorCal Cannabis pulling 159g/sqft
PPF
The Photosynthetic Photon Flux (PPF) measures the number of photons within the PAR range emitted per second by a light fixture. It is measured in μmol/seconds. Basically, PPF indicates how much light (photons) is coming out of a light fixture.
It’s important to note that PPF isn’t a measurement of how much light reaches a plant, just how much is being emitted by the lamp. Not every lamp with the same PPF is as effective at bringing that light down to the crops. Some lamps may have less focus, allowing light particles to spread out wide and be wasted on your walls. However, by considering the PPF of a grow light, you can get a fair estimate of the number of lamps needed to reach your required light level on the plants.
Photons emitting at wavelengths above 700nm do not contribute to the PPF and are not measured, and neither do ultraviolet wavelengths, anything below 400nm. A lamp can be producing inordinate amounts of ultraviolet and infrared light and they would contribute nothing to the PPF.
In order to test the PPF of a fixture, it must be put into an integrating sphere that is connected to a sophisticated instrument known as a spectrophotocolorimeter. This machine tests the PPF, the spectral distribution chart, it gives the color rendering index (CRI), and also an idea of the PPE based on a specific input. Fohse runs it at 100, 75, 50, and 30 watts to determine how efficacious the lights are at various outputs so you know exactly what you’re getting.
PPFD
The Photosynthetic Photon Flux Density (PFFD) is a measurement of the number of photons that make it to the plant. It is the number of photons within the PAR zone that fall on a given surface each second, expressed in micromoles of photons per square meter per second, or μmol/m²s.
It’s measured with a radio spectrometer, or PAR meter, a small device that you place on your plant under a lamp. The device indicates exactly how many photons are hitting its sensor, which is tiny. Because of the sensor’s size, it’s important to get measurements in many areas on a plant and average them together to get a real idea of the overall PPFD of a light fixture.
Many things can be adjusted to achieve the desired PPFD, from the height of the lamp to the spacing of the plants. Some manufacturers incorporate lenses or reflectors to achieve more focused PPFD. This can result in a lower PPF, so growers will have to weigh whether it’s better for their grows to have more photons hitting the plant directly, or more photons being emitted in general.
Fohse F1V @ Remedy Cultivation
DLI
The Daily Light Integral (DLI) measures the total amount of light received in one day or “photoperiod” by a plant. While PPFD shows how much light arrives in a particular spot per second, DLI measures how much light was received in the designated area in total for the whole day, or the number of moles (not micromoles) of photons per square meter per day, expressed as mol/m²d
Still not getting it? Think of it this way. If light were rain, PPF would be the amount of rain coming out of a cloud, PPFD would be the amount of rain hitting the ground at a single time, and DLI would be the total amount of rain that reached the ground during the day.
When creating a lighting plan, it is important to determine your desired DLI. In a greenhouse or grow room, lighting consistency is crucial to growing healthy plants. With indoor grow rooms, it's a bit less complicated, as you don’t have to account for the sun. Simply determine the quantity of photons you want your plants to receive. Too little, and the plants will produce larfier buds, which are smaller, leafy buds that are less commercially viable. Too much light, and you could actually send your plant into photorespiration, where it will burn more carbon than it consumes, and shrink and shrivel into a sickly little sapling.
After determining the target PPFD, you can find the target DLI with some simple math:
Target PPFD x 60 s/min x 60min/hr x 12 hr/day = Target DLI
1,000,000 µmol/mol
“To determine the target DLI, growers need to first determine their target PPFD. Traditionally recommended PPFD levels for cannabis range from 700-900 µmol/m²s, but by adding more CO2 into a grow room, cultivators can push their light levels to 1500 µmo/m²sl and kick their plant growth into overdrive. By adding CO2, the ratio of carbon to oxygen in the air is altered enough to allow the plant to avoid photorespiration by providing it with enough carbon to meet its rate of photosynthesis.”
PPE
The Photosynthetic Photon Efficacy (PPE) measures a light fixture’s ability to convert electrical energy into PAR light. This is expressed as micromoles of photons per Joule of energy used. The better a light’s PPE, the more energy-efficient it is, meaning less money spent on energy for the grower.
The formula for PPE is PPF/watts of power used, meaning PPE does not take into consideration the PPFD of a grow light. A grow light can claim a high PPE, meaning that its PPF is higher using less energy, but from what we know about PPFD, this doesn’t necessarily mean you’re seeing a benefit from that higher efficiency.
In fact, there are several ways to manipulate a lighting fixture to have a higher PPE that could have negative effects on the light’s output, and your crop’s growth. To learn more about how manufacturers can manipulate PPE ratings, check back next month for the continuation of this three-part series.