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It took a while, but people finally understand that watts don’t measure visible light output. Lumens do. Watts has to do with energy consumption, not light output. Getting some folks to understand that was a tough nut to crack, and I’m guessing some still don’t have a handle on it.

Humans Love Lumens. But Plants? Something Else.

Steve Maurer, IME
It took a while, but people finally understand that watts don’t measure visible light output.

Lumens do.

Watts has to do with energy consumption, not light output. Getting some folks to understand that was a tough nut to crack, and I’m guessing some still don’t have a handle on it. I suppose it comes from the long reign of incandescent light bulbs.

It’s easy to see the confusion. A 100-watt bulb is brighter than a 60-watt bulb. But the actual light output was still measured in lumens. For example, a standard 60-watt incandescent bulb typically produces around 800 lumens, while a 100-watt bulb produces around 1600 lumens.

But newer tech, first fluorescents and then LEDs consumed less power while giving the same visible light output. And because people still were, and perhaps still are, tied to the ancient ways, boxes of CFLs and LEDs have the “wattage equivalent” printed on the label.

Even though it’s a misunderstood comparison.

Lumens provide a means to compare the brightness of different light sources by indicating how much visible light is emitted, based on the sensitivity of the human eye to different wavelengths. However, they do not provide information about the quality of the light, its color, or its efficiency in terms of energy usage.

I was pretty confident in my understanding of lumens versus wattage versus color temp. Then … along came horticulture lighting.

Plants care more about light quality than intensity
In horticulture, lumens aren't a very useful measure. Plants "see" and use light differently from humans. They use a wider range of wavelengths for photosynthesis, particularly in the blue and red regions of the spectrum, not just the green region where human vision is most sensitive.

That means a light source with a high lumen output might not necessarily be useful or efficient for plant growth. Plants don’t walk around … people do. Even people working with plants.

Here are some terms you need to understand if your customers are horticulturists. They may want to grow flowers, fruits and veggies, herbs, and other botanicals, either inside a grow house, inside their own house, or even outdoors.

And yes, commercial cannabis growers might be in your list of valued customers, too.

Proper lighting can positively enhance the health and growth of plants.

The jury’s still out on talking to them, at least in my opinion.

Photosynthetic Photon Flux (PPF)

Warning! We’re going to get a little acronym crazy here. But it beats having to type of some of these terms by hand.

PPF measures the total amount of Photosynthetically Active Radiation (PAR) produced by a lighting system each second. PAR is the range of light wavelengths that plants use for photosynthesis, typically 400nm to 700nm. It's a count of the number of photons in this range that a light source emits each second.

Unlike lumens, PPF isn't weighted towards any particular part of the spectrum - it treats all photons from 400-700nm equally. This makes it a much more useful measure for horticulture since it tells you how much useful light for photosynthesis a lighting system is producing.

However, PPF still doesn't give the full picture because it doesn't take into account how evenly the light is distributed across the plant canopy, which is where Photosynthetic Photon Flux Density (PPFD) comes in. So we’re not done yet.

PPFD (Photosynthetic Photon Flux Density)

No, we’re not going back to the future with a flux capacitor. Although that would be fun.

PPFD measures the amount of PAR that actually arrives at the plant, or as it's often put, the number of photosynthetically active photons that fall on a given surface each second. This is an essential measurement because it tells you how much of the light emitted by your lighting system is actually reaching your plants.

Remember, plants need light for photosynthesis. And the more light, the better the production.

Whether natural or artificial, if you want your plants to flourish, they’ve got to have light, and the right kind of light to boot. Here are some quick explanations of how light affects photosynthesis. By the way, photosynthesis is the process where they convert light, water, and carbon dioxide into glucose and oxygen. The quality, quantity, and duration of light all influence plant growth.

Light quality refers to the color or wavelength of light. In the light spectrum, different colors are associated with different wavelengths. Plants use certain colors or wavelengths of light for photosynthesis more than others. Specifically, chlorophyll, the pigment responsible for photosynthesis, absorbs light primarily in the blue (430-450nm) and red (640-680nm) regions of the spectrum. Blue light is generally associated with plant growth and development, while red light is more related to flowering and fruiting.

Light intensity, or quantity, is the amount of light that a plant receives. It is usually measured in units of lumens or photosynthetically active radiation (PAR). The intensity of light that a plant receives can affect the rate of photosynthesis. More light often leads to more photosynthesis, up to a certain point.

Too much light can be harmful to plants, causing what's known as light saturation. In fact, too much light can lead to photooxidative damage. Sheesh!

Finally, light duration, or photoperiod, refers to the length of time that a plant is exposed to light. This can have a significant impact on the growth and development of a plant. Some plants require long periods of light each day (long-day plants), while others require short periods of light each day (short-day plants).

Yeah, I know. Unless you’re an avid horticulturist yourself, it could get a little complicated to give your customer what they need, particularly if they start throwing these terms around. Honestly, you’re best bet is to contact a lighting rep that’s knowledgeable about this stuff and has the products necessary.

Let them guide you through the garden maze and light your path to success.
Photo courtesy of TCP Lighting
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