Growers have more lighting options today than ever for cultivating plants and while there are seemingly hundreds of different grow lighting vendors on the market, it seems as if each of them have different terminologies for their PAR metrics.  Some vendors aren’t even consistent with their own product material.   It is truly the Wild West in todays grow lighting market, and because of the wide variety of ways grow lighting vendors present these metrics, its very easy to get mislead and confused.   In today’s entry, we’re going to discuss the various ways in which PAR metrics are presented and what those metrics actually mean for you.


Before we go through the variety of ways in which grow lighting companies present their PAR metrics it is important to understand PAR.  PAR, short for Photosynthetically Active Radiation, is the spectral range of solar radiation released as photons in the 400-700 nm spectrum.  Photons are particles of light that move in different wavelengths.  Red photons have longer wavelengths with less energy, and blue photons have shorter wavelengths and more energy.  Both red and blue photons, along with others are vital to the photosynthetic process.  During this process plants use light (photons), CO2, and water and convert them into sugars.  Sugars are used to create more plant tissue and as biological energy to stay alive.   PAR is the measurement of all this usable light that is specifically emitted within this range of absorption.  It’s also very important to note that the measurement of PAR is strictly a measurement of light intensity without correlating actual spectral emission and how this relates to spectral efficiency and actual absorption.  PAR is not weighted.. all light photons in this range are grouped together as one value.  For this reason, PAR is only one half of the equation of growing power by a grow light with the other half being spectral emission.  PAR measurements = Light intensity

Photosynthetic Photon Flux (PPF) is the total amount of light (photons) emitted from a light source over time (one second).  It is measured by using the unit micromoles per second (µmol /s1).   The PPF of an artificial light source can only be measured in an integrated sphere.  Here are some of the different terminologies grow light vendors use to present their PPF values:

  • PPF
  • µmol PAR/s
  • µmol/s or µmol/s1
  • PAR output
  • PAR
  • Photon Flux
  • uMoles/s

These are only are few terminologies used by grow lighting vendors for presenting the PPF metrics but note that they are in reality all the same thing.

PPF = How much light is being emitted


PPF Efficacy

Growers and lighting vendors that have measured the PPF of an artificial light can easily determine the PPF efficacy of that light source.  Efficacy is the measurement of how well a light source produces PPF with the amount of energy (watts) that it’s consuming.  It is important to always use the actual input wattage of a light source rather than “max” wattage of a lamp or LED.   Like with PPF, vendors have no real consistent way of presenting these metrics.  Here are a few examples:

  • PPF/J
  • PPF/W
  • PAR Efficacy
  • Efficacy
  • µmol/J
  • µmol/w
  • Umole/J
  • uMoles/s/W

Again, all of these values mean are referring to the same exact thing which is PPF Efficacy.

PPF Efficacy = How efficiently is the fixture using electricity to emit its amount of light

Photosynthetic Photon Flux Density (PPFD) is the total amount of light hitting a square meter area at certain distances from a light source.  PPFD can be measured with a quantum or PAR light meter using the unit micromoles per meter squared per second (µmol/m2/s1).   Quantum or PAR light meters calculate an average the amount of photons hitting a square meter of surface area per second.  These types of meters can be a bit misleading, because there are many variables outside of the light source that can affect the reading of the sensor, such as the refraction of light of off the walls or floor, adjacent fixtures, and/or other objects within a room that can deflect or reflect the light.  The only way to get a true apples to apples comparison is if the PPFD of different light sources are measured in the exact same environment.  Here are a few different terminologies that vendors are using to present the PPFD metric:

  • PPFD
  • µmols
  • Average PPFD
  • Centerpoint PAR
  • uMoles
  • µmol/m2/s1
  • PAR (Umol)-PPFD


While some white LED light based companies have worked hard to mislead consumers with the argument of PPFD over PAR measurements in terms of µmols, they are in fact seemingly unknowingly talking about the same thing.   If you’ll reference the websites of the very manufacturers of PAR meters such as Apogee, you’ll see that a quantum PAR meter is in fact measuring PPFD.

PPFD = Light energy emitted over a given area (square meter)

PPFD Footprints              

Many vendors offer PAR (PPFD) footprints of their light at different distances to show the uniformity of there light over a given area, such as a squared meter or a 4’x4’ space.  These footprints are created by measuring PPFD levels using a quantum or PAR meter at multiple points over a given surface area.

Example PAR Footprints at Different Distances from Light Source


Again, calculating PPFD footprints can be a bit misleading because the many variables outside of the light source that can affect the reading of the sensor.  If you’ll note in this illustration above taken from a prominent online re-seller, there can be huge variances even within a perfect square reading depending on other factors.  This is one reason why PAR footprint results are of little actual use to the consumer when evaluating brands.  Since grow light power depends on more than just intensity, the most important factor when laying out lights in your space are the actual, effective coverage areas of each light.  Whether or not these coverage areas are being accurately reported by a given manufacturer is indeed another topic altogether.

 As we know, the only 2 factors that determine the growing strength of a grow light are how bright it is and what type of spectrum it’s emitting.  That’s it.  The entire cornerstone concept of LED grow lights is to create 100% usable light through efficient spectral output that matches to the rate of spectral absorption by green chlorophyll and to provide this as brightly as possible.  Thus, we need to evaluate the PAR output from light to light to give us that intensity level and we need to do it with as much of a level playing field as possible by using a proper benchmark that clearly illustrates the intensity level without the ability to manipulate it.

The only light intensity metric that cannot be faked or otherwise manipulated is a direct, center point test stated in terms of  µmols.  This is why we at PlatinumLED offer this direct comparison as a benchmark:  because it’s unable to be manipulated and provides a standardized benchmark.  If any company refuses to provide this metric, there’s typically a reason why they’re hiding it and that is under performance.  Further, it’s important to note that without either video verification of these PAR tests or verifiable 3rd party tests, PAR numbers provided on a website should be taken with some skepticism.

Until the entire grow lighting industry decides on a set of PAR standards there will undoubtedly be confusion for growers and it’s very important to cut through the hype and marketing to get to the actual facts instead of the dizzying amount of terms being thrown around.  Remember, if you don’t know what ‘PAR’ metric a grow lighting vendor is providing, you can always call and ask.   There are also large and vocal communities of growers who have used many of these lighting brands successfully.  In addition to looking at wattage consumption, spectrum and PAR metrics, you should be also reading reviews, looking at forums, and talking to other growers about what works.  These are all great ways to find the right light for your needs as the most important proof is the actual result from growers themselves.


Happy growing!