Grow Light PAR, PPF, and PPFD Values Decoded
When browsing grow lights, you’re bombarded with acronyms that can be easily confusing. Photosynthetically Active Radiation (PAR), Photosynthetic Photon Flux (PPF) and Photosynthetic Photon Flux Density (PPFD) are the three most common (and confusing) phrases used by grow light manufacturers and resellers.
With the mass wave of marijuana legalization, people are jumping into the home cannabis growing game, so it’s important to understand all three phrases defined here if you plan to grow cannabis plants (or other) at home.
By understanding these fairly basic measurements you’ll be able to purchase a LED grow light that’s truly appropriate for your plants’ needs and the amount of grow space you’re using.
We’ll answer questions such as:
- How many moles/micromoles of light do my cannabis plants need during each growth phase?
- How to determine the true effective coverage of an LED grow light
- What LED grow lights offer PPFD values high enough to satisfy my plants?
- How to measure the PPFD output of your current grow light
- What to do if your current grow light isn’t strong enough
Photosynthetically Active Radiation (PAR), UV-A and Infrared:
Photosynthetically active radiation (PAR) is the range of light wavelengths that enables photosynthesis in plants. The actual range is from 400 to 700 nanometers (nm).
Ultraviolet and infrared wavelengths are just below and above each end of the PAR spectrum, and are often included in grow lights because they have specific benefits to plants.
Ultraviolet actually has 3 distinct wavelength ranges (UV-A, UV-B, and UV-C) of its own, but only UV-A is beneficial to plants. UV-A measures at 310-400nm.
It’s actually a damaging wavelength so it’s included in small amounts in grow lights. UV-A triggers the same defensive proteins in your plants’ as if they were being eaten or attacked by insects, so it makes your plant more resistant to insects as a result. Perhaps more importantly, UV-A has been shown to increase THC, CBD, and terpene production in cannabis plants.
Infrared (IR) comes in at the top range of the PAR spectrum at 730nm. It can also be damaging if your plants get too much exposure, so only a couple IR diodes are included in LED grow lights.
The plant protein phytochrome is sensitive to infrared wavelengths. Plants use this protein to regulate the switch from vegetative to flowering phases. A grow light that incorporates the proper amount of IR light will result in full stem growth, proper node spacing, and higher yields.
Simplifying PPF / PPFD values:
There are two other phrases related to photosynthetically active radiation (PAR). Those phrases are Photosynthetic Photon Flux (PPF) and Photosynthetic Photon Flux Density (PPFD).
PPF simply describes the amount of photons within the PAR wavelength range that are produced by your grow light in one second of time. PPF is measured in units called micromoles (umol). You can use PPF to determine if your grow light is “strong enough” for your plants.
PPFD is the amount of photons that hit a surface (or your plant canopy) in a given second. It’s also measured in micromoles (umols).
The difference between PPF and PPFD is that PPF is the actual strength of light produced by your grow light, while PPFD is the strength of light that touches your plant’s leaves. There’s a distinction because the light loses intensity as it travels from source to endpoint.
The more important number when buying a grow light is PPFD. What good is a grow light with PPF of 1500 umol if the PPFD is 10 umol? The answer is it’s no good. So you definitely want to focus on the Photosynthetic Photon Flux Density (PPFD).
PPF and PPFD are measured in micromoles, but eventually all the micromoles absorbed by your plant adds up to moles. One mole is one million micromoles. By the time your plant has absorbed 1 million micromoles of light, it has absorbed 1 mole of light.
When a grow light’s PPFD is 900 umol per second, it adds up quickly over a 12 or 18 hour lighting cycle. This is how we’ll determine later if a grow light is strong enough for your grow space or not.
As an example, a popular grow light advertises the PPFD values shown in the image below:
It’s easy to see the Photosynthetic Photon Flux Density (PPFD) values on the chart above and think “higher is better.” But a higher PPFD value isn’t better beyond a certain intensity.
Instead, there are two main factors in determining if your grow light supplies a sufficient PPFD intensity.
The first factor is figuring out if a grow light supplies enough moles of light to your plant over the course of your 18 or 12 hour lighting cycle (more on this later).
The second factor is determining “effective” coverage area based on your grow light’s PPFD values at various points underneath the light. PPFD values change at different distances from the exact center location underneath a grow light. They also change at different hang heights.
Remember, PPFD is the intensity of photosynthesis activating light touching any given surface. So the second factor is figuring out how much of your grow light’s claimed coverage area truly has high enough PPFD value for your plants to grow.
So how do you determine the first factor – if your grow light supplies enough light to your plants each day? We break down the math below.
How much PPFD do cannabis plants need?
Fruit or vegetable bearing crops need between 20 and 40 moles of light per day. That’s true for cannabis as well. The amount of light delivered to your plants in a 24 hour period is also known as the Daily Light Integral (DLI).
Therefore the bare minimum DLI needed by your plant is 20 moles, or 20 million micromoles (umols) per day. To deliver 20 million micromoles per day to your plants, your grow light will need to put 308 umol on your canopy for 18 hours straight during vegetation. During flowering, it’ll need to put out 462 umol for 12 hours straight.
That means the PPFD values outside of that 1×1 ft area shown on the chart below are not even enough to hit a bare minimum 20 moles of light during either growth phase.
Technically you’d have enough for the vegetation phase if you were growing 1 plant in that 1×1 square foot space. But it’s not enough for that plant once flowering phase rolls around.
The bare minimum total light may be 20 moles per day as described above, but most growers aim for 40 moles, or 40,000,000 umol per day to maximize their yield.
As P.L. Light Systems elegantly puts it,
The production curve from a crop in relation to the amount of moles delivered per day sharply increases between 20-30 moles, begins to really level off between 30-40 moles and over 40 begins to hit a point of diminishing returns for your crop.
So ideally, you’ll want to provide your cannabis plants 40 moles of light if you really want the maximum yield. Above 40 moles per day the additional crop yield levels off.
If you’re aiming for 40 moles per day, it means your LED grow light will need to produce 617 umol for 18 hours straight during vegetation, and 926 umol for 12 hours straight during flowering. Any grow light producing PPFD values less than that is not enough.
This is why we like to give conservative coverage estimates in our best LED grow light reviews. Manufacturers can place a chart showing 50-100 umol at 4ft wide coverage points, but what does that really mean? Its not much more than marketing, and some people truly can’t tell the difference.
It’s best to measure your effective coverage based on the area where your light is emitting the bare minimum calculations we described above. If your light isn’t hitting those levels, you need a more powerful grow light.
How did we arrive at these PPFD values?
First we converted the bare minimum amount of moles of light needed per day into micromoles. The bare minimum 20 moles = 20,000,000 micromoles.
Next you need to divide by the amount of time your grow light would be shining on your plants.
During vegetation most people set their grow lights to 18 hours on/6 hours off.
So 20,000,000 micromoles/18(hours)/60(min per hour)/60(sec per minute) = 308.6 umols needed to hit 20 moles throughout an 18 hour vegetation lighting period.
20,000,000 micromoles/12(hours)/60(min per hour)/60(sec per minute) = 463 umol of light needed for 12 hours straight to reach 20 moles of daily light during a flowering lighting period.
Repeat this calculation with 40,000,000 micromoles to see how we arrived at the micromole numbers for the 40 mole per day target.
How Can I Measure My Grow Light’s PPFD Values?
If you already own a grow light and you’re concerned whether the PPFD output is high enough, you can measure your grow light’s PPFD output with this PPFD meter:
This is a highly rated PAR meter that’ll tell you if your grow light PPFD is strong enough for your cannabis (or other) plants. The wavelengths of light detected by this meter are the exact wavelengths you want on your plant. It measures 390nm to 690nm wavelengths – the PAR wavelengths.
This Apogee MQ 500 PAR meter is tested to work with LED grow lights as well as high pressure sodium (HPS) and metal halide grow lights (MH).
Just to reiterate, you’ll want the following PPFD readings on your plants:
20 mole/day (the bare minimum PPFD): 308 umol across whole coverage area for 18hr during vegetation. 462 umol across whole coverage area for 12hr during flowering.
40 mole/day (the maximum PPFD): 617 umol across whole coverage area for 18hr during vegetation. 926 umol across whole coverage area for 12hr during flowering.
If you aren’t getting these minimum levels of PPFD then you need a stronger grow light.
Which Grow Lights Provide Sufficient PPFD Output?
Below we’ll go through three LED grow lights that provide sufficient PPFD for your marijuana plants (or other plants). These aren’t the most cheap LED grow lights, but you’ll get what you pay for. These are among the best LED grow lights due to their PPFD capability.
We’ve reviewed the G8LED in more detail here, but for the purpose of this article we’ll only be discussing the G8LED grow light’s PPFD measurements and coverage area.
Does the G8LED provide enough PAR intensity for your plants?
The answer is yes, and perhaps more importantly, it does so over a considerable coverage area. This is one of the best LED grow lights on the market. I’d like to focus on the image below:
Hang this light at the standard 18-inch level, and you’ll receive strong enough PPFD to get your plants in a 2-3 square foot coverage area through vegetation and flowering. If you add in G8LED’s recommended booster light as well, you’ll be even better off.
Does the Phlizon 2000 watt COB LED grow light provide enough PPFD intensity for your plants?
The Phlizon 2000w is a very powerful COB LED grow light that will get you a good effective coverage area. While Phlizon doesn’t provide a chart of the PPFD coverage, they do tell you that they measured 2161 umol directly under the center of the light, while hanging at 18 inches. That’s incredibly powerful. I’d personally estimate that you’ll be able to get a solid 3 square feet of 700umol + coverage from this COB LED grow light.
An added bonus is this Phlizon grow light is a bit more affordable than our first pick. The 1000 and 2000 watt variants of this light are highly rated from dozens of customer reviews. This is one of the best LED grow lights if you’re looking for sufficient PPFD intensity and a large coverage area.
This King Plus 3000 watt LED grow light will spread sufficient PAR light intensity onto your canopy. A strong PPFD value of 1582 while hanging at 18″ is enough to cover 2 square feet effectively.
The King Plus 3000 watt is a cheap LED grow light that actually provides a sufficient PPFD value for your plants. The light has been reviewed hundreds of times and has a near perfect rating.
What if you own Grow Lights that don’t have strong enough PPFD levels?
Maybe you’re reading this information after you’ve purchased grow lights and you want to improve your situation. If that’s your case, don’t worry, you can easily add PPFD intensity without throwing out your current grow light.
Bloom booster grow lights are an affordable yet effective way to increase PPFD intensity over a small area.
Hitting that minimum 20 moles per day can be tough with a cheap grow light. Even moreso when you switch to the flowering phase and have 6 less hours of light exposure.
The flowering phase is equally important to the end quality of your cannabis harvest. The vegetative phase sets the stage, but red light intensity is directly correlated to the weight of your final harvest.
If your canopy simply needs a PPFD “boost” instead of a whole new light, you can consider one of these grow lights below:
This red wavelength booster light will add considerable PPFD value boost for a 2 foot space. People who bought this bloom booster left some pretty enthusiastic reviews, including that it noticably enhanced the buds and their plants love it.
That’s right, I’m recommending a 300 watt Mars Hydro for use as a bloom boosting LED light to bring your PPFD values up to sufficient levels. Why does this light serve as a perfect PPFD booster? The cost of this light is quite low, yet the PPFD values up to 1.5 square feet are impressive enough to considerably boost light intensity in your existing grow space. Add in the fact that this light is daisy chainable and you can add as many as you need.
Having a sufficient PPFD intensity for your plants is the most essential factor to consider when buying an LED grow light or setting up a grow space. We tried to make it easy for you to dig through the marketing and figure out what PPFD values you’ll truly need to maximize your cannabis yield (or other plant’s yield).
Aim for a minimum of 20 moles of light per light session. Aim for 40 moles if you want to really maximize yield. Follow these guidelines for obtaining a proper PPFD output and you’ll be growing like a pro.