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Understanding Lumens, Lux and PAR Differences in Grow Lights

Lumens, Lux and PAR Differences

Does it ever feel like you can’t make informed grow lighting decisions without a degree in electrical engineering? As technology advances, it seems the metrics essential for understanding grow light quality become more complicated. The truth is, it’s easier than it seems. And the most important thing to understand is lumens, lux, and PAR differences.

These distinct measurements cause a lot of confusion, especially among new growers. Home growers and hobbyists know these terms all relate to light intensity, but they’re not sure how they’re different. 

But knowing this difference is absolutely essential because only one of these metrics is relevant to your plants. Here is your clear and simple guide to lumen, lux, and PAR differences.


Why Lumens, Lux, and PAR Differences Matter

All three of these metrics—lumens, lux, and PAR—tell us something about the quality of light a lamp emits. But the important distinction among these three measurements is who benefits from that light quality: you or your plants.

Lumens and lux refer to light intensity as it is perceived by the human eye. PAR, on the other hand, tells you something about the quality of light as plants perceive it.

Think of it as a dog whistle. If you bought a dog whistle based on what your human ears could hear, you’d end up with a pretty ineffective purchase. A dog whistle isn’t made for your perception, so it’s a mistake to judge it that way.

LED grow lights work the same way. In many other lighting applications, we talk about lumens and lux because we usually use lights to see. But when you’re selecting grow lights, your top priority must be your plants’ perception. You need to understand lumen, lux, and PAR differences so you can choose a light that emits photons your crop can use.


Lumens and Lux: Measurements for Humans

 First, some quick definitions.

 Lumens measure the intensity of light output as it is visible to the human eye.

 Lux specifies the intensity of light in a given area. One lux equals one lumen per square meter.

 To put it in the simplest terms, lumen and lux measure what we would more casually refer to as “brightness.” This is where lumens, lux, and PAR differences are especially important.

You see, the human eye can only perceive certain wavelengths. The wavelengths at the center of that range—green, orange, and yellow light—appear brightest to our eyes. Those at either end of the spectrum—blue and far red light—take on a dimmer appearance.

Meanwhile, your plants use a lot of the red and blue light spectrum, while doing very little with green light.

You see the problem? A light that boasts high lux or lumens may do a great job of illuminating a room. But those measurements don’t tell you anything about what that lamp can do for your plants. That’s where PAR comes in.


PAR: Measurement for Plants

 The value of PAR is right there in the name: photosynthetically active radiation.

 PAR refers to the range of light your plants use for photosynthesis. PAR wavelengths range from 400-700nm. The PAR output of a lamp is often measured using a PAR meter to identify the number of photons emitted within the PAR range.

 Now, when you select a grow light, your ultimate goal is to provide your plants with sufficient PAR. But it’s important to understand that a PAR measurement alone cannot tell you how much quality light actually reaches your canopy. There are a couple other metrics you should know. 


First, there’s PPF, or photosynthetic photon flux. This metric expresses the number of PAR photons a light fixture emits per second.

In the lighting industry, we measure PPF as part of our commitment to accuracy. Traditionally, there has been some fluctuation in light quality in grow lights from moment to moment. This fluctuation isn’t enough for your eyes to perceive a flicker, but it has been enough to warrant additional measurements so you know how many PAR photons your lamp emits on average.

Currently, high quality LED grow lights like those at California Lightworks provide a far more consistent output. There is almost no fluctuation thanks to advanced technology, but we still measure PPF as a matter of standard practice.



Quick recap: 

PAR tells you how much usable light your grow light emits. PPF tells you how much usable light your grow light emits per second.

PPFD (photosynthetic photon flux density) tells you how much usable per second actually reaches your plants.

Light quality declines as you move farther away from the light source. The PAR your grow light puts out is much greater than the PAR that reaches a canopy 18” away. Of course, this is one reason why LED grow lights are exploding in popularity right now. Because LEDs radiate less heat, you can close the distance between the lamp and the canopy a little more. This means a greater dose of PAR photons reaches your plants.

In any case, PPFD is the number to look for when you compare grow lights. 

Now that you understand lumen, lux, and PAR differences, here comes the big question:


Does Your Light Manufacturer Know Lumens, Lux and PAR Differences?


It may seem silly to ask, but with home grows and indoor cultivation on the rise, a lot of entrepreneurs are looking to make an easy buck selling LED grow lights. 

These businesses know how to market a product and source cheap LEDs in China. They are vaguely aware of LED grow light buzzwords. 

They do not know the science of cultivation. They are not familiar with the most essential grow light metrics. They have no idea how your plants use light or how the right light can increase yields and product quality.

If you come across a grow light advertising light quality in lumens or lux, consider it a glaring red flag. This is a manufacturer who does not know lumen, lux, and PAR differences. 

Instead, look for a company that gives you the right measurements and can even provide details about the testing process. A reliable LED grow light manufacturer can explain the full technical details of their lights and talk shop with you.

At California Lightworks, our U.S.-based customer support team will even discuss our lights in the context of your specific grow operation. We help you determine the best lights for your setup and calculate your potential ROI. We can answer questions about installation and operation. 

We love all questions, big and small, because every question is an opportunity to serve the growers who inspire us. If you could use a little guidance or would like to learn more about our top-tier LED grow lights, drop us a line.


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