Guide to Measuring LED Horticulture Lighting

LED Horticulture Lighting

The terminology and measurements used to describe and characterize LED horticulture lighting can be confusing and overwhelming. If you’ve been researching LED horticulture lighting companies, you’ve likely found that they are prone to use a variety of acronyms and measurement jargon that tend to confuse even savvy cultivation professionals.

At SpecGrade, our lighting engineers are at the forefront of LED lighting technology for horticultural applications, therefore it is important to us that we use precise vocabulary and sophisticated measurement techniques to ensure our products are performing at the top of their game, and that this performance is accurately communicated to our growers. That being said, we’d like to clarify some of these terms for you and sort out the signifiers you should be paying attention to as you compare LED grow lights for your horticulture facility.

How to Measure Light for Plant Growth

Much of SpecGrade’s product line and engineering legacy has taken place in the world of commercial and industrial LED lighting, which is largely designed to accommodate the needs of the human eye. We use the saying Lumens are for Humans as a reminder that light intended for human vision is measured in lumens. Often this is quantified by LUX or foot candles over a given space.

However, plants have a much different relationship with light than we humans do. Measuring lumens only captures the central curve of the lighting color spectrum, because that’s what our eyes can perceive. It leaves out a broad range of the spectrum on either end, including red (600-700 nm) and blue (400-500 nm), which are vital to driving photosynthesis. That’s why we don’t use lumens to calculate and measure light for plant growth.

What is PAR?

The central term we use for measuring light in horticulture is PAR, which stands for Photosynthetically Active Radiation. Since plants rely on a much broader spectrum of light for healthy growth (400 – 700 nm), PAR metrics define the quality and amount of available light that pertains specifically to plant growth. Using quantum sensors, grow lighting engineers can accurately quantify the intensity and amount of PAR within a beam of light.

When evaluating the performance and quality of LED grow lights, it’s important for professional cultivators to consider 3 key questions;

  1. How much PAR does the fixture produce (PPF)
  2. How much of the PAR emitted from the fixture actually reaches the plants (PPFD)
  3. How much energy is used by the fixture to make this PAR available


PPF stands for Photosynthetic Photon Flux, and quantifies the total amount of PAR emitted by a lighting fixture every second, measured in micromoles per second (μmol/s). Since PAR is only a slice of the total light a given fixture will produce, PPF measurements are an important indicator of how effective an LED grow light is at nourishing plants with the necessary wavelengths for driving healthy growth.


Where PPF is simply a measurement of the amount of PAR created by the light, PPFD or Photosynthetic Photon Flux Density is a determination of how much of that PAR actually reaches the plants.  As we’re fond of pointing out, not all LED grow lights are created equal. Professional growers are interested in the overall ROI of their investment in high quality grow lights, especially in the competitive world of commercial cannabis. Therefore, it’s important to consider the end result of a lighting fixture’s beam spread on the plants, not just what the fixture throws.


Beware of LED Grow Light manufacturers publishing

only a single PPFD number for their fixtures!


To accurately assess a grow light’s efficiency in delivering a uniform level of PAR across an entire section of crop, it is important to take multiple measurements within a given area to calculate an average. Simply listing the PPFD from the center point of a 8×8 section of the crop is not a sufficiently accurate representation of the PAR reaching your plants as a whole.

Uniformity is a core principle of SpecGrade LED grow lighting technology, so we always publish our PPFD measurements in relation to a given mounting height, area of measurement, and min/max range of several measurements to demonstrate the carefully calibrated even spread our fixtures are designed to provide.

Photon Efficacy

Driven by the grand claims made by many horticulture lighting manufacturers, growers often make the mistake of focusing on the total electrical watts of a lighting fixture to determine its intensity. However, watts only tell you something about the energy going into a lighting fixture. The important factor is the light actually coming out of the fixture, and of course how much of that light is usable PAR.

Photon Efficacy is how we measure a fixture’s efficiency at converting available watts into quantifiable photons of PAR, calculated at micromoles per Joule of energy (µmol/J). SpecGrade LED grow lights lead the industry in photon efficacy, with remarkable energy efficiency directed specifically toward maximizing PAR output. Our attention to robust engineering has made our LED grow lights powerful engines of efficacy and the carefully sculpted LED optics ensure maximum PPFD for large crops and bountiful harvests.

Comparing LED Grow Lights for Professional Cultivation

With a sufficient crash course in the important metrics of professional LED grow lights, we invite you to compare SpecGrade LED grow lights with those of our competitors. Armed with an understanding of PAR, PPF, PPFD, and photon efficacy, along with a range of other factors that affect the quality of horticulture lighting fixtures, you’ll find that we’ve produced some of the most advanced lighting instruments on the market.



For more information about SpecGrade LED grow lights, please contact our office at (614) 868-5337 to speak with our expert staff. Our cultivation partnerships have helped us push the boundaries of quality grow lighting technology, and we look forward to working you too.