Performance Metrics: How to measure if your LED grow lights are working the way they should

Performance Metrics: How to measure if your LED grow lights are working the way they should

For people who grow plants for a living, looking at the performance metrics of your LED grow lights can be quite a process, often with a steep learning curve.

Growers learn quickly that it’s just not as simple as putting a plant under a light bulb and when you start researching lighting, the questions can start piling up. After all, you are a grower and not a scientist!

But when you grow plants, you do have to have a basic understanding of science, especially when it comes to LED grow lights because understanding these systems is a technical and scientific process.

And one way you can do that is to learn to interpret the metrics used to define and measure the way light is emitted.

While growers have to look at plant growth holistically – keeping in mind that no single  factor is to blame for spectacular growth or dismal performance – there are some ways to look at whether your LED grow lights are giving your plants what they need to thrive.

What you shouldn’t do, as a grower, is isolate numbers and attribute one factor as the key thing in your overall success. At the end of the day, growers have to consider so many things: Water, carbon dioxide, nutrients, temperature and lighting – when looking at performance metrics.

But we can talk about LED grow lights and address how lighting can play a crucial role in optimal plant growth – because it does!

One of the first things a grower should do is test different grow lights on their plants to see which ones are the best fit. It isn’t a one-size-fits-all situation with LED grow lights. After all, growers are creating a mini-ecosystem with lighting as one part of the equation – and plants can only absorb so much light.

Types of light and how it’s measured

When you start learning about light, one of the first lessons is the different types of light. One type, visible light, is what humans can see. The other, photosynthetically active radiation or PAR, is what drives photosynthesis (and makes plants grow). This is a simplistic definition, of course.

Once you figure out the types of light, it helps to next learn how to measure it. In a nutshell, you measure visible light in a few ways and you measure PAR in another. Since we are talking about plants here, we’ll talk about how we measure PAR, because plants use photons, or PAR, for photosynthesis.

And two of the main metrics used to measure if your LED grow lights are working as they should are PPF and PPFD.


PPF stands for photosynthetic photon flux and is the total PAR produced by your lights every second. It’s not measured in terms of energy, like watts, it is measured in terms of photons and the term micromoles.

PPF is measured at the light source and so, as a metric, it isn’t going to accurately tell a grower how much light is actually reaching the plant – or how that light is distributed. PPF doesn’t tell you where the light is hitting the plant and it can’t be measured by growers; it needs to be done at the factory level so growers have to trust their light manufacturers when they tell them what it is.

PPFD, which stands for photosynthetic photon flux density, is the No. 1 metric in the grow light industry, as it can be measured using a meter.

Since PPFD is a metric that considers how much light is actually reaching the plant, its considered superior to PPF. And it can be used to measure and compare lights when growers are trying to figure out the best option.

However, PPFD isn’t always perfect. It doesn’t tell you how much light is reaching your plants and it isn’t a cut-and-dried metric, meaning that it can be manipulated and skewed. Mainly, this is done by measuring at a very close range that is unreasonable for most growers to maintain, or by measuring only the parts of the plant that are receiving the most light).

So, while PPFD is currently the best metric growers have to measure how their lights are performing, it is fallible and needs to be used with some degree of caution and skepticism.

Other factors

LED grow lights are mostly science, but there is an art to them as well. This is where things like uniformity come into play. So, what is uniformity? It is basically the light fixture’s ability to distribute light evenly over the canopy of your plants. Light needs to be uniformly distributed so plants get consistent light and there aren’t hot spots or dark areas. You can measure uniformity using PPFD.

Efficacy is another metric to use to see how effective your grow lights are. To learn the efficacy, you take the PPF and divide by the wattage to learn how much usable light your fixture produces each second.

Why is efficacy important? You want to be at about 277 volts – which is the industry sweet spot. Once you cross over this voltage threshold, additional costs come into the equation.  That’s the lowest amount of energy usage (aka dollars spent on energy bills) to get the highest return on investment (ROI).

The Key Takeaway

So, what is the key takeaway here for growers? Successful growers separate themselves from the pack by going with a trusted LED grow lights manufacturer who will give accurate PPF readings and by not falling for marketing hype when it comes to PPFD numbers. By buying a few different lights and seeing which ones produce the best results over time, growers can choose the correct grow lights – and not make a decision based on marketing buzz.