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PAR Requirements

notforgodz
Theoneandonly Z

PAR = photosynthetic active radiation.
This is light between 400-700 nanometers. This spectrum of light known as PAR, is the only spectrum that plants use for photosynthesis.

I’m not sure what u mean by PAR requirement? There is no such thing IMO. Its either u use light in that spectrum to grow plants or don’t use it at all and grow nothing.

I think what ur looking for is how can u provide ur plants with the highest PAR rating. At the same time take in to consideration umol/s count. This will let u know how many molecules of light are emitted per second. As far as the bottom of the plant, look into the calculations of how to determine the PPFD (photosynthetic photon flux density). Remember though that light intensity decreases as you move away from origin, so instead of worrying about anything growing on the bottom. Train or prune ur plants so that ur main growth is getting equal light throughout ur plant

chazbolin

uMoles and Moles represent intensities, as in the number of photons of light within the PAR region are striking a meter squared per second. Based on the spectral distribution of the inda-gro 420 lights I use I target hybrids with an average of 20 mole/day. You can think of umoles as the number of raindrops hitting a bucket every second. Moles is how many inches of water accumulate within the bucket.

You can learn alot from this paper but starting in the middle of page 16 you’ll learn about umole and moles/day. http://www.inda-gro.com/pdf/MeasuringPlantLight.pdf

notforgodz

Thank you for your replies and excellent answers. It is obvious you guys know your stuff.
So sorry for not correctly asking my question. I was tired and looking at some reference material on Induction/LED’s dealing with a spectroradiometer. What I meant to ask is, what luminosity (or brightness) would the lower branches require for proper growth? I hope that this is the proper term. 🙂

Theoneandonly Z, that is an excellent idea about trimming and kinda along the lines of why I am asking this question. Once I know what base intensity the plant requires, I can use my light meter to trim to depth.

chazbolin

Unless I’m running vertical lighting I’ll partially defoliate the lower 1/3 of my plants since not much light is going to get through a dense canopy anyway. Those canopy fan leaves are like little solar panels but they will block light. What light does get through will be a result of canopy movement and at lower intensities as a result of the distance from the light.

When flowering at the tops I like to see a broad spectrum lamp (I get this with an 18″ lamp-canopy separation) emitting 600-700 uMoles over my 13 hour lights on cycles. This gives me between 28-33 Moles/Day which from my experiences with Indica dominants has been ideal. If I have multiple lights and put the lamp-canopy distance @ 12-14″ that same 13 hours will put me in the 40 Moles/Day region for Sativa dominants. There’s a Moles/Day chart on page 17 of the link I gave you that will make this easier to understand.

On a 4 ft plant with good canopy movement I aim to get an average of 200-300 uMoles at the lower flowering sites but unlike the canopy where light is a constant intensity this is going to be an irregular reading unless you LST. If I’ve got multiple plants running taller than 5 ft I’ll run the vertical VPAR light, no defoliation and pick up the lower branches that way.

Amber

Unless I’m running vertical lighting I’ll partially defoliate the lower 1/3 of my plants since not much light is going to get through a dense canopy anyway. Those canopy fan leaves are like little solar panels but they will block light. What light does get through will be a result of canopy movement and at lower intensities as a result of the distance from the light.

When flowering at the tops I like to see a broad spectrum lamp (I get this with an 18″ lamp-canopy separation) emitting 600-700 uMoles over my 13 hour lights on cycles. This gives me between 28-33 Moles/Day which from my experiences with Indica dominants has been ideal. If I have multiple lights and put the lamp-canopy distance @ 12-14″ that same 13 hours will put me in the 40 Moles/Day region for Sativa dominants. There’s a Moles/Day chart on page 17 of the link I gave you that will make this easier to understand.

On a 4 ft plant with good canopy movement I aim to get an average of 200-300 uMoles at the lower flowering sites but unlike the canopy where light is a constant intensity this is going to be an irregular reading unless you LST. If I’ve got multiple plants running taller than 5 ft I’ll run the vertical VPAR light, no defoliation and pick up the lower branches that way.

Tried doing a search but got kicked for not enough letters…even after using a phrasing a question and using a parenthesis. It occurred to me, while…

Understanding Grow Light PAR, PPFD, Wattage and DLI

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.

It’s important to understand all the phrases defined here if you plan to grow cannabis plants (or other plants) at home.

By understanding these fairly basic measurements you’ll be able to purchase a LED grow light that’s appropriate for your plants’ needs and the amount of grow space you’re using.

I’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 light actually has 3 distinct wavelength ranges (UV-A, UV-B, and UV-C), but only UV-A is beneficial to plants. UV-A light measures at 310-400 nanometers.

Ultraviolet light is a damaging wavelength so it’s included in small amounts in grow lights. UV-A light 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 infrared 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 infrared light will result in full stem growth, proper node spacing, and higher yields.

What is PPFD?

There are two other phrases related to photosynthetically active radiation (PAR) that you need to understand when growing cannabis. Those phrases are Photosynthetic Photon Flux Density (PPFD) and Micromoles (ÎĽmols).

PPFD is the amount of light photons that hit a surface (your plant canopy) in one second. It’s measured in units called micromoles (μmols). Simply speaking – it’s the strength of the light that reaches your plants.

The light loses strength as it travels from source to endpoint (from grow light to plant). You’ll notice on most grow light intensity charts, the PPFD numbers decrease with increased distance from the light.

That’s why paying attention to your grow light hanging height is so important when growing cannabis.

What is Daily Light Integral (DLI) and What DLI does Cannabis Require?

The daily light integral is when you take those PPFD numbers and add them up over the course of one day. Since PPFD numbers are measured per second, in the course of one day you can end up with millions of micromoles.

1,000,000 ÎĽmols = 1 Mole of light.

Fruit or vegetable bearing crops need between 20 and 40 moles of light per day. That’s true for cannabis as well.

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.

Below I break down how much PPFD is needed for each phase of cannabis growth in order to achieve 20 or 40 micromoles of light per day.

How Much PPFD Do Cannabis Plants Need During Seedling, Veg and Flowering?
PPFD During Seedling Phase
(18 hr daily light cycle):
PPFD During Vegetative Phase (during whole life for autoflowers)
(18 hr daily light cycle):
PPFD During Flowering Phase
(12 hr daily light cycle):
Moderate Cannabis Yield (minimum light needed): 200-300 ÎĽMols 306 ÎĽMols 463 ÎĽMols
Max Cannabis Yield
(max light needed):
200-300 ÎĽMols 617 ÎĽMols 925 ÎĽMols

Cannabis seedlings require only 200-300 PPFD per second during the first three weeks of life.

To deliver 20 moles of light per day to your plants, your grow light will need to put 308 umol per second on your canopy for 18 hours straight during the cannabis vegetative (veg) phase.

During the cannabis flowering phase, the grow light will need to deliver 462 umol per second for 12 hours straight in order to achieve 20 moles of light per day.

If you want to increase the amount of light from 20 to 40 moles per day, resulting in higher yields, you simply need to double the numbers above – 308 PPFD to 616 PPFD during the vegetative phase, and 463 PPFD to 925 PPFD during the flowering phase.

How Much PPFD does Autoflowering Cannabis (Autoflowers) Need?

If you’re growing autoflowers you should stick to the recommended vegetative phase light intensity range of 306-617 micromoles for the whole life of the plant.

That’s because autoflowers remain under 18 hours of light per day for the whole life cycle. If you switch to the higher flowering light intensity when your autoflowers begin to flower while maintaining 18 hours of light, you’d risk burning the plants.

How to Read a PPFD Chart:

The image below shows an LED grow light’s PPFD map, which shows PPFD readings at certain spots beneath the grow light. This example shows a grow light that’s too weak to grow cannabis.

The PPFD values outside of that 1×1 ft area shown on the chart below are barely even enough to hit a bare minimum 20 moles of light during either growth phase.

So when you’re purchasing a grow light, make sure it’s strong enough. Don’t opt for the most inexpensive model, or you’ll regret it.

Technically you’d have enough light for the vegetative 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.

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 I calculate these PPFD values?

First I 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 the vegetative phase 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 vegetative phase 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 intensity numbers for the 40 mole per day target.

Can I Increase or Decrease the Intensity (PPFD) of My Current Grow Light?

Yes, there are two ways to do this. The first is by using the dimmer function, if your grow light has one. The second method would be to simply adjust the hang height of your grow light.

Keep in mind the higher your grow light is hanging, the larger area it covers but the weaker the light will be. The lower your light hangs, the light will be more intense, but it will cover a smaller area.

There’s a law of physics called the Inverse Square Law. This law says if you know the intensity of your grow light at one height, for example 1000 micromoles at 18 inches, then every 12 inches of additional height will reduce the intensity by 75%. So if your 1000 micromoles of light at 18 inches is raised to 30 inches, the intensity will be reduced to 250 micromoles.

This makes it easy to estimate the intensity of your grow light without using any tools. As long as you know the manufacturer provided (or self measured) intensity at one height, you can know with certainty the intensity at another height.

To read more about grow light hang height, read my article on the topic here: Grow Light Hang Height.

How Do I Measure My Grow Light Intensity (PPFD)?

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:

Apogee MQ 500 Full Spectrum PAR/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).

Unfortunately the Apogee meter seen above is a bit expensive. There’s also another less expensive (but slightly less accurate) method of measuring your grow light intensity – by converting Lux to PPFD.

Some smart phones are able to measure lux because modern smart phones have a light sensor on the screen-side of the phone. If your phone doesn’t have a light sensor (download the Lux meter app and try), or if your phone isn’t measuring properly, you can purchase a Lux meter for next to nothing.

Once you’re able to get a lux reading, take that number over to Waveform Lighting’s Lux to PPFD calculator, select the light source closest to the light you’re using, enter the number of lux you measured, and press calculate!

You can also try the Apogee conversion calculator as well.

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 the vegetative phase. 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 the vegetative phase. 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?

Many grow light options provide sufficient light strength for growing cannabis. To be safe, I recommend avoiding the least expensive grow light models, and sticking to a major brand like HLG, Viparspectra, Mars Hydro, or another brand vetted and named on my blog.

You can watch the informational video I made on this topic below, or take a look at one of the recommended lights on the list below. I also wrote a separate article on calculating grow light coverage.

Either way, as long as you follow the steps laid out here, you should be able to find yourself a high quality LED grow light!

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.

High Yield/High Quality – for 4×4 feet:

Scynce Raging Kush

There’s nothing not to love about the Scynce Raging Kush. Fully customizable white spectrum, control via phone app, and incredible intensity over an entire 4×4 space.

I personally think it’s the best LED grow light on the whole market, and in terms of emitting intense enough light over your grow space, it certainly does the job.

Does the Scynce Raging Kush provide enough light intensity (PPFD) 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 images below showing the flowering and vegetative light modes:

Hang this light at the standard 18-inch level, and you’ll receive strong enough PPFD to get your plants in a 4 by 4 foot coverage area through the vegetative and flowering phases.

The best part about this light is the spectrum is fully customizable through a phone app, if you like to adjust or experiment with spectrum, this light’s definitely for you.

Click here to see the Scynce LED Raging Kush at LED Grow Lights Depot

High Yield/High Quality – for 2×4 feet:

Green Sunshine Co. Electric Sky 300 (ES300)

Does the Green Sunshine ES300 grow light provide enough PPFD intensity for your plants?

The Green Sunshine ES300 is a very powerful LED grow light that will get you an amazing effective coverage area. The strong light intensity lasts all the way to the edge of the 2×4 foot grow space.

Owners of this light absolutely love it, and to paraphrase some of their reviews from Green Sunshine’s site, a grower with 10 years of growing experience said the ES300 resulted in the fastest growth they’ve ever seen. They also complimented the great customer service from the Green Sunshine Company.

There are many other reviews from people who switched from cheaper LED grow light models like Viparspectra or Meizhi. They say the difference is night and day.

If you need an strong and efficient grow light that truly covers your entire space, Green Sunshine’s Electric Sky 300 (ES300) is the way to go.

Click here to see the Green Sunshine ES300 at LED Grow Lights Depot

Medium Yield/Budget Option – for 2×3 feet:

Mars Hydro TSL-2000 Watt Quantum Board Grow Light:

These new Mars Hydro TSL-2000 watt LED grow lights will spread sufficient PAR light intensity onto your 3×3 canopy. They also happen to be my budget choice because they’re so damn affordable.

The only difference is you’ll be trading lower price for more of a moderate coverage area and intensity compared to lights emitting the maximum light intensity.

I think you can throw two of these units in a 4×4 and have a very solid setup.

The quantum board design features a sleek, fanless, lightweight, and energy efficient setup at an entry level price. This light is hard to beat on value.

Click Here to Check Out the Mars Hydro TSL-2000 Watt on Amazon

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:

#1. G8LED 90 Watt RED Flowering Booster LED Grow Light

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.

#2: Mars Hydro TS-600 LED Grow Light

That’s right, I’m recommending the TS-600 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.

The white light spectrum plus infrared will boost any phase of plant growth. Can’t go wrong with a few of these to brighten up your corners!

What’s the Deal with Grow Light Wattage?

Figuring out wattage is especially confusing with grow lights. It’s the unfortunate result of marketing tactics companies use to make somewhat similar grow lights look different.

True grow light wattage can be determined by figuring out how many watts your grow light pulls from the outlet.

Metal Halide (MH) and High Pressure Sodium (HPS) grow lights are simple because the watts number you see in the name is typically what’s being pulled from the outlet.

But with many modern LED grow lights, there are two wattage numbers to understand.

The first is the total number of watts in the LED chips themselves. A “2000 watt LED grow light” is probably using two hundred 10 watt LED chips, and that’s why it’s called 2000 watt. But a grow lights’ power is better measured by how much electricity it pulls from the wall, and that’s the second number.

The wattage at the wall for a 2000 watt LED grow light might only be 500 to 600 watts. This is a more accurate number because the light intensity (PPFD) is more closely correlated to wattage at the wall. This explains why the light intensity can vary widely among grow lights all claiming to be xyz number of watts – they’re each consuming varying levels of wattage at the wall.

How much PAR does my marijuana or vegetable plant need to maximize harvest? Find out the minimum PAR value you plants need before you buy a grow light.