Think Beyond White LED Grow Lights [Kelvin and Color Temperature]

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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.

You’ll learn how White LEDs and Grow Lights have been originally designed for eyes and how you can interpret this information.


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.

Your eyes can pick up green and yellow easily, but red and blue color is hard to see.  Source:

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.

HPS vs Metal Halide:

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.



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.


Spectrum response of white LED temperatures (source)

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.

Guess what?

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.

Interesting right?


Different Light Source Spectrums

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?

If you’re want to know even more about light, you won’t want to miss out on this video.

What has your experience been with grow lights labeled by color temperature.

How did they perform?

Comment with your thoughts below!


93 thoughts on “Think Beyond White LED Grow Lights [Kelvin and Color Temperature]

  1. Brenton Willis Reply

    I’m so glad that the folks at The Green Sunshine Company know what they’re talking about. I’m new to all of this and until I found TGSC I was lost. I tried to research but there are far too many inconsistencies in product information. Typically choosing an LED off amazon comes down to marketing and not science. I ordered the v3 180 after reading reviews from everywhere I could find about TGSC. I am blown away by this company! I feel like I stumbled upon something special with them. Somehow I have managed to feel quite confident in purchasing an expensive 200 watts! Kudos to TGSC! You are obviously all loving what you do and the results speak for themselves. You are developing a very loyal following, myself included! Thanks folks

  2. Don Walker Reply

    Just wondering if a cool white led shoplight would work on tree seedlings indoors. From nut germination(chestnuts) to keeping indoors for 2 months before going outside

  3. Steve Reply

    Really nice to find this well ….Seminar really
    I found it most enlightening. Thanks for sharing , you’ve obviously developed a great product 👍 Viva Le Internet

  4. Ronette Walsh Reply

    Mike Penn,
    Kudos to you! very well said.
    & wm also excited to see what new advances and, technology(ies) will bring the lighting arena.maybe even BRINGING ”sunlight” through a,daunting,dark winter will be enough to ward off SAD;SEASONAL AFFECTIVE DISORDER.which is very think Ican be faked into a sunnier,happier place,with fake lighting,AND get the satisfaction of watching my houseplants flourish,at the same time!..blows my mind with complete gratitude and deep appreciation.I really am hopeful,and pun intended,joy-filled to say,”I CAN See the light….”.watching my plants die off each winter is depressing enough. these ordinary led bulbs just may fix that,and more! Im hopeful this is just the beginning of a new welcomed adventure?

  5. Nicole L Reply

    Can you please tell me what light source would be best for a snake plant then (that is in an area that doesn’t get much light)? The floral shop I bought it from said its low maintenance and doesn’t require much light, but it’s leaves are starting to spread a bit instead of being stiff/upright as when I first bought it. I don’t water it much at all (per their instructions) so I would like to get a small grow light for this corner of my home, but would prefer knowing what would be best. I don’t want it necessarily growing a ton, I just want it healthy and thriving. Thank you!

  6. Bryan Wright Reply

    Interesting information. Thank-you. I’m primarily interested in keeping my citrus plants happy during Illinois winters.

  7. Michelle Brennan Reply

    I want to grow salad greens indoors. You are saying 4000K is best for full cycle, but I dont want flowering. I currently have a 6500K Florescent but would like to add LED. What would you suggest I use?

  8. Gajah Duduk Reply

    Thanks for even yet still more info on this. Based on this, what is the ideal kind of light set up to use to grow tomatoes indoors? KISS!

  9. Mike Penn Reply

    Wish I had come across this article sooner. Through trial and error, I came to roughly the same conclusions for myself on the subject of grow lights detailed in this piece.

    It occurs to me that there remains a lot of refinement to be made with newer and emerging technologies and methods. I also realize that the appearance of visible light is little indication of spectra qualities, given constraints of our vision. It is an interesting time to explore grow lighting though. To me, at least, seeing in my short lifetime, a transition from the ubiquitous mainstream incandescent and occasional though mostly commercial florescent lighting, which went on to CFL’s once smaller tubing needed could be mass produced to house it’s modified design of florescent lighting, and now seeing the majority of lights of all kinds being replaced with LED’s, which are of near overwhelming variety and distinction, not to mention with new improvements and advancements refined and brought to market constantly. This all means that a wealth of research and findings will also take place and certainly further define what is ideal. I think that automation and artificial intelligence are barely beginning to be integrated to their capacity in lighting, and this is one area where a tremendous amount of improvement should take place. Particularly considering ways to integrate both the subtle and the more substantial changes that naturally occur with sunlight over time, whether hour to hour or week to week. It will be interesting to see how AI and automation in conjunction with lighting technologies such as LED can be used to efficiently carry out small, or subtle spectral changes in light over time and continue to improve efficiency, reduce waste, and even recycle energy output. Additionally, research and findings that can recreate Earth’s atmospheric conditions in relation to light, such as wuth the use of applying film coverings or layers of nano-particles to replicate atmospheric conditions, will also continue to be refined. There are even methods of capturing and re-emitting natural sunlight at different locations without converting the energy or altering the light properties and without the use of mirrors or reflective qualities. It is not the least bit far out to think in the next ten years that actual windows could be replaced by artificial replicas and could look and feel no different to us or to our plants than the real thing. That has always drawn my interest. The effects of light and that artificial light has on us, as understood psychologically, but also in terms of everyday, practical, economic, and general sense of living is concerned. Recreating what the sun does naturally, manipulating light creatively, and artistically designing lighting to reproduce natural conditions is an area of research and development where methods have been limited by the technologies themselves. Newer and less cost prohibitive technologies with more efficiency, greater variability, and better quality, can support tremendous innovation.

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