Efficacy in LED Grow Lights


PAR (Photosynthetically Active Radiation):

PAR refers to the spectral range of light radiation within the visible range of light which supports photosynthesis, between 400 to 700 nanometers.

PPF (Photosynthetic Photon Flux):

PPF refers to the total amount of photons within the PAR range produced by a lighting fixture each second. This is expressed in micromoles per second (μmol/second).

PPFD (Photosynthetic Photon Flux Density):

PPFD is a measurement of usable photons which reaches one square meter of a given surface every second, and is measured in micromoles per square meter per second (μmol/m2/s). Whereas PPF is a measurement of the total amount of photons produced by a light, PPFD is essentially a spot measurement.

Efficacy (Photon Efficacy):

Efficacy is a measurement of how effective a grow light is at converting electrical energy into photosynthetically active radiation. This is calculated by taking the PPF value and dividing it by the measurement of wattage (Joules per second). Therefore, efficacy measures exactly how much usable light a fixture produces every second per watt used. (µmol/J)

Efficacy is not the same as efficiency

White-light LED companies have recently taken to claiming that above all, efficacy is the most important feature of a lighting fixture, some going so far as to boast the efficacy of a single diode, not the entire fixture. They claim a fixture’s spectral quality is secondary to efficacy, and warn against companies that claim their spectrum is specifically tuned for the benefit of plants. However, this is a false assertion and a deliberate misrepresentation of the numbers to mislead consumers.

Efficacy represents a light’s capacity for turning electrical energy into photons, and is merely a measurement of how many photons within the PAR range a fixture emits per second. But since not all light within 400 to 700 nanometers is used by a plant in equal amounts, a light’s spectrum is vital to the growth of plants. It’s become well known that blue light is the most important part of the light spectrum for vegetative growth, while red light is ideal for the flowering cycle. For this reason, reputable LED grow light manufacturers engineer their spectrum to focus on the parts of the spectrum that most benefit plants, not humans.

White-light LEDs produce a large amount of green and yellow light. While these spectrums play a vital role in plant development, they are effective in considerably smaller amounts than red and blue light. Thus the ratio of light spectrum becomes very important. The amount produced by white light LED manufacturers far exceed the amount a plant can actually absorb, and more than 50% of that light is merely reflected from the plant’s surface, increasing the temperature of the grow environment.

White Light LED Spectrum

White Light LED Spectrum

Studies have shown that a low percentage of green light (≤ 24%) actually enhances plant growth, whereas plant growth is inhibited under a higher percentage of green light. When we look at the above spectrum, we can see that a large percentage of the fixture’s energy is devoted to light within the 500-600nm range. The vast majority of this energy will be wasted, as it will not do much to help with the growth of the plant.

A white-light LED with a great efficacy value can flood a plant with a ton of photons, and the plant will do well enough, however there will be a considerable amount of energy wasted in order to produce that growth. A plant can only absorb so many photons, and they are not absorbed in equal amounts. The vast majority of green and yellow photons will wind up wasted as heat. A fixture with a lower efficacy value and an optimized spectrum with the ideal amount of green and yellow light can provide superior results with considerably less wasted energy.

So how important is efficacy?

The fact that a considerable amount of the light emitted from white light LED fixtures is wasted calls the importance of efficacy values into question. PPF is measured by a machine called an Integrating Sphere, which measures all of the photos between 400-700nm emitted by a fixture regardless of how much of that light reaches the plants, so it’s inadvisable to put too much stock into a high efficacy value. Efficacy alone means little without context. When you consider that 50% or more of the green and yellow light from a white-light LED fixture is wasted, and that green and yellow light make up a sizable percentage of a white light LED’s spectrum, a high efficacy value suddenly seems misleading. You would be better served by a fixture with a targeted spectrum that may have a lower efficacy value.

LED Grow Light targeted spectrum

Kind LED Grow Lights Targeted Spectrum

Some white-light LED companies have warned against companies which claim to have a “magical growth spectrum” but there is nothing magic about it. This is science, pure and simple. While light science is an ever-evolving field of study, we’ve learned a lot about how the various parts of the spectrum affect plant growth. Blue light, vital in the vegetative growth stages, mimics the direct sunlight plants receive during summer months. In the late fall and winter months, the sun doesn’t rise as high in the sky, and the sun’s path causes rays to hit the earth at much more of an angle, forcing the sun’s rays to pass through more atmosphere, which affects the spectrum. As the shorter blue wavelengths are scattered throughout the atmosphere, this causes the spectrum to appear more red. This is known as “Rayleigh scattering,” and is why we see the sky as blue, and why the evening sun appears more red. By carefully including the proper ratio of light across the entire spectrum of usable light, you are replicating mother nature in the most optimized way, taking advantage of millions of years of plant genetic evolution, ensuring your plants thrive, and not wasting energy producing light your plants will be unable to absorb.

What should you look for in an LED Grow Light?

When judging a grow light, you can’t point to a single feature as being the most important. There are several factors that influence the viability of a grow light, with the spectrum and the intensity of that spectrum being at the top of the list. Any company that is directing you towards a single number on a white sheet is trying to distract you from other deficient components of their panel. Kind LED Grow Lights has carefully crafted a perfect-blend spectrum for their grow lights that ensures no energy is wasted on parts of the spectrum plants will not use to grow and thrive.

So we must ask ourselves, considering all of the numerous shortcomings, why is the commercial industry still dominated by white light fixtures? There are a number of reasons, but perhaps the biggest reason is that white light LEDs are already used in every industry imaginable for human visibility, which speaks to the viability of the technology over traditional lighting methods, but unfortunately an efficient diode for human visibility is quite the opposite for your plants, irrefutably inefficient, regardless of the specs of the diode. The research and development into white light diodes is much further along—they are readily produced by many large manufacturers, and because of this availability are considerably less expensive than producing diodes with a specially targeted wavelength. This means bigger profits for the companies using these diodes. Often, the efficacy of these diodes is better on paper than the alternatives, which gives the companies the ability to market these specs, despite the fact that efficacy alone does not make a grow light effective. Ultimately, Marketing has spun a company cost-saving measure for themselves into a selling feature and in doing so has manipulated a large percentage of growers into believing that it’s the best way to grow.

It could also be because it’s the type of light we’re all used to seeing—it more closely resembles how we see the world. For growers used to growing outdoors under the sun, switching to white light LEDs may be an easier transition. For those moving away from traditional HPS lighting, white light LEDs might be easier for them to get used to. White light LEDs are a comfortable way for people who want to experience some of the benefits of LED grow lights to do so without changing the appearance of their grow facility. But it’s important to remember that LED grow lights exist for the benefit of plants, not people. White-light LEDs may be easier to manufacture and photograph better, but these are human conveniences. A targeted spectrum is much more beneficial to plants, and ultimately, that is what matters for commercial grow facilities everywhere.


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