Have you heard about “Color Temperature” and which is right for each stage of plant growth?
Trying to find the best grow light and wondering on the spectrum?
Cool White or Warm White? How about Neutral White?
All white light sources are categorized by how something appears to your eye. You may have seen Kelvin (K) or Color Temperature (CCT) before:
- Cool White (6500K, 6000K, 5000K) looks more “blue” and “green” to your eye
- Warm White (4000K, 3000K, 2700K, 2000K) looks more “yellow” and “orange” to your eye.
Have you wondered how lights designed for eyes could somehow work the best for plants?
Do plants really need blue light for vegetative growth and red (warm) light for flowering growth?
In this article you’re going to learn how to think beyond color temperature for plants, and learn how White LEDs and Grow Lights have been originally designed for eyes and how you can interpret this information.
Ready? Let’s dive in…
Color Temperature (Kelvin) Means Almost Nothing For Plants
I must be crazy, right?
Consider this, your eye can mostly pick up green and yellow, that’s it.
Here’s the thing…
White LED manufacturers make the LED chips so that they can “score” the highest lumen rating (the light your eyes can see). Green and yellow are “boosted” to get the maximum lumen brightness.
Higher lumen rating = More Sales
This means that “Color Temperature” is actually the most sensitive in the Green and Yellow regions.
What’s more is that white LEDs are specifically designed to reduce the colors plants want most for growth – red and infrared light.
Since your eye can’t see them very well, the LED’s spectrum is designed to leave those colors out.
This means that Blue and Red can change significantly, but your eye can barely pick up the difference.
Take this for an example…
An LED vs CFL bulb might look similar to your eye, but will grow your plants drastically differently. — All because of how different red and blue is.
See how both CFL and LED Lights might look similar to the human eye, but the red and blue regions are drastically different, meaning different results with plant growth.
Cool & Warm CFL
Cool & Warm LED
Look at how much “variance” there is outside yellow and green…
Heck, two 3000K LEDs from two manufacturers actually throw off different spectrums!
I hope you can see by now, that color temperature really tells us nothing about how plants will respond to them.
A 5000K Florescent will grow differently than a 5000K LED…
Not only that, but two LEDs of the same color temperature from different manufacturers could also grow differently!
The “Cool White/Blue is for Veg” and the “Warm White/Red is for Flower” Myth
Ask any grower, and they’ll tell you blue is for veg and red is for flower.
Do you know why?
Do they know why?
It’s just what we’ve been told….
Where did this myth come from?
“HPS” bulbs were meant for street lamps, and they turn out to be great for flowering, but lack the proper amount of blue light to keep plants compact.
“Metal Halide” bulbs were also meant for street lamps, and they turn out to be better for veg, since they contain more blue than an HPS, but HPS is more efficient and has more “oomph” in flower.
Since neither is perfectly balanced for all stages of growth, we’re in the mantra of “switching” the spectrum from veg to flower.
How far have grow light manufacturers taken this myth?
Look at the LED lights on Amazon, they all have “veg” modes ranging from an extreme neon blue to a cool white. Each “veg” and “flower” spectrum is so different, plants will grow differently from light to light depending on the ratio of red, green, and blue light.
What might pique your curiosity is that too much blue will actually stunt plant growth.
What? Yep. Read 7 Myths Grow Light Companies Tell You to see more about that.
Many growers actually prefer “warm white” LEDs in veg. The reason for this, is that at the “warm white” color temperature, the “ratio” of wavelengths is ideal for plants.
3000K/4000K (warm) LED spectrums happen to have an ideal amount of blue light, and a good amount of yellow light for growth power. Even though red and infrared are mostly left out, it’s a decent growth spectrum.
Go any lower to 1000K, and the blue light will drop below what is good for plants.
Go higher than 5000K, and so much red light is left out from the spectrum your plants will grow slowly and without much vigor. This is the reason why “blue” colored spectrums are not ideal for flower, they lack growth power wavelengths (red/IR).
So, do plants really need blue for the vegetative stage of growth after all?
Yes, plants require some amount of blue light so they don’t “stretch” and search for light. Plants can sense the % ratio of blue light they receive to determine how to grow.
But at the end of the day, plants will “veg” and “flower” under any kind of light. They don’t “need” blue for veg and they don’t “need” red for flower, heck, they’ll even grow under a completely green light source from start to finish!
Plants are resilient like that, they deal with what comes to them.
We can help them out and provide them with a better spectrum than what we’ve been limited to with the “neon blue and red” LEDs with narrow band technology, or the “cool/warm white” LEDs that are designed to be brightest to the human eye.
Growers and grow light manufacturers are just using the technology that is easy to find & readily available to them: LEDs designed for humans to see.
What you should realize is the ratio of colors significantly affects how a plant will grow, down to the speed of growth and shape of the leaves and stems. A well-designed single spectrum with the correct “color characteristics” can work well from seed to flower for all stages of growth.
Your Eyes Can’t See it, But Plants Can
Plants have been growing for eons under the sun, but we humans haven’t been very good at understanding how light affects plants.
First, many scientists believed that plants “only used” red and blue light.
If you were wondering, it’s only a coincidence that older “narrowband LED” technology makes blue and red colors. In actuality, blue and red light are the only colors older LED technology can make very well, and this is why you see so many “purple” LEDs out there.
The previous belief about plant science and the emergence of red and blue LED lighting technology have been a “match made in heaven” for the LED manufacturers claiming a “perfect spectrum” since old technology matched an outdated scientific belief.
Then, a study was released by Dr. McCree that tested a plant’s response to one color at a time showing that plants use much more than red and blue light.
He uncovered a discovery that plants use color from 400nm – 700nm. The term “Photosynthetic Active Radiation” (PAR) was coined.
As you can see above, White LEDs fall into this 400-700nm range, and don’t create much light outside of it, so they’ll score a very high “PAR” reading or “umol/J” efficiency rating, but keep in mind, efficiency doesn’t grow plants better, the spectrum does.
A 3.0 umol/J grow light may actually grow worse than a 1.8 umol/J grow light if the spectrum is inefficient for plant growth — would you take efficiency over good plant growth? Generally speaking, the more colors a grow light creates, the less “efficient” it will become, especially when we’re talking about LED.
If you’re wondering why I’m saying this, consider what Dr. Emerson figured out about plant growth and light.
He discovered that two colors could “work together” to create “bonus” photosynthesis and plant growth, including those colors above the accepted “PAR” range from 400-700nm.
This not only means “PAR” is insufficient to measure how light will help plant growth, but it also tells us that plants care about the reactions between multiple colors at a time, especially those in the Infrared range.
Red, Blue, and Infrared ratios actually are extremely interesting. When a plant doesn’t receive any Infrared light, it acts differently to color. You could say that a plant has a natural way of growing (with infrared) and an unnatural way of growing (without infrared).
This is why at the Green Sunshine Company we measure our Electric Sky Wideband Grow Lights in what is known as “Extended Photosynthetic Active Radiation” or EPAR for short which measures the full range of light between 300 and 800 nanometers of light.
We should be measuring the full ability of a grow light to create colors that affect plants.
What you’ll see in the industry next is significant innovation cycle towards spectrum research, and here are some things that you might want to watch out for…
Plants care about a “Ratio” of light
If you can imagine, plants have “minimums” and “maximums” of each color where plant growth will go way out of whack if the spectrum steps out of those bounds.
All White LED spectrums do not take plants into consideration, so blues, greens, yellows, reds, and infrareds can bounce all over the place as they shift from “cool” to “warm”, and can adopt color ratio combinations that are not ideal for plant growth.
Maybe the spectrum will grow way too stretchy, or maybe it will have too much blue which stresses out the plants and stunts growth, or maybe not enough green and infrared for canopy penetration… you get the idea.
Read our Spectrum Efficiency Showdown article to learn more about how the ratio of colors affect plant growth.
It’s hard to find the “ratio” by reading a spectrum graph
Reading a spectrum graph is actually quite difficult.
Sure, there will be a curvy line on a graph, and the line will go higher and lower, so you might think that the taller the line, the more light there is of that color.
But that isn’t true for plants.
Remember, plants look for a ratio of color within the spectrum.
This means we care about the total area of the colors of blue, green, and red, not just how tall the line goes on the graph.
Notice that if the “peak” of one color goes up, it doesn’t always mean that there is the most of that color.
What do you think?
Did you learn something new? What has your experience been with grow lights labeled by color temperature. How did they perform? Comment with your thoughts below!