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 full spectrum grow light and wondering on the actual spectrum for your indoor garden?

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 How Grow Lights Work 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 led plant 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!


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

  1. Gino Reply

    Hello! Im going to buy a led grow light, and it has 2200k and 5000k. it is good for flowering and vege cannabis? is 3000k better than 2200k? The led has 30.000 Lumens and 213w, it is for 80cm x 80cm indoor, (2.6ft per 2.6ft) Thanks!!!!!!

  2. Abelard O. Añana Reply

    Hi your article is so complex and hard for me to understand as a newbie to growing plants. I just bought 4000 k with 630nm-660nm led grow lights for my variegated monsteras, will this type of led grow lights good for variegated plants or even encourage more variegation? Thanks 😊

  3. geegee Reply

    whats best for flowering cannabis ? 3500 all across the bord or a mix of 3000k and 5000k

  4. Jeremy Reply

    I’ve always been told the same thing, blue is for veg and red is for flower. Now, I know better!

    Thanks for the information!

  5. Billy Reply

    I have a bizarre approach…Far/Deep red first 1/2 hour then 3000k overhead trigger while Far/Deep red continue for an hour. Then Far/Deep turn off and mid side canopys turn on 5000k while main overhead 3000k quantums 301H continue…..Still with me?….At mid day uva/uvbs turn on for 1 1/2 hrs combined with side and overhead lighting….After that everything goes in reverse equal intervals to as it began finishing in 1/2 hr Far/Deep red to darkness…
    Equaling 11 hrs 3000k 301h
    3 hrs Far/Deep red
    9 hrs side canopy 5000k adjustable red,white,blue 5000k 3500k 2800k
    4 timmers
    Final outcome…Legendary!!!

  6. Wayne Kirby Reply

    I’m experimenting with using a mix of warm white & daylight (2700k & 5000k) household 14 watt (100 watt equivalent) led light bulbs as grow lights. Wondering about mixing in a few other k values. I started 50/50 with the bulbs. Added more 5000k bulbs, actually seems to have slowed growth. Considering replacing some of the 5000k bulbs with some more around 3000-3500k. Any suggestions welcomed!

  7. 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

  8. 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

  9. 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

  10. 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?

  11. 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!

  12. Bryan Wright Reply

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

  13. shane Reply

    I’m even more confused than before I mean can u possibly sum up at the end and just say what is bloody good for a plant indoors less more middle none of the above you gave great info but no definitive answer that I could actually see and for someone with Aspergers I’d just love an answer at the end of all the information cheers

  14. 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?

  15. Emma Wilson Reply

    I’ve always been told the same thing, blue is for veg and red is for flower. Now, I know better. Thanks for the information.

  16. 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!

  17. 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.

  18. Andrea V Reply

    Hi there,
    Great article… Although, am I the only one who had a hard time understanding some of it? Lol I’ve tried reading and educating myself on lots of Different grow light articles, and I find myself having a hard time understanding the material because of my lack of knowledge in that area. That, and the fact that almost every article I ready has a different opinion on grow lights. So thank you for actually providing facts and research behind your article. With that said, I use 2-24w bright white LED “full spectrum” grow light strips per shelf. At the distance I keep my lights to plants it says it has a PAR value of 210.7unol/m2/s. Do you think these lights are sufficient for my succulents? I haven’t noticed any negative effects , yet. Thank you

  19. JT Reply

    How about the distance of the light bulb from the plants ? Would 5 ft be good ?

  20. Maiga Reply

    Thank you for this information!
    There is a corner in my house with very little light and I’d like to have some of my plants there (green leaves).
    I understood that 3000K/4000K LED would work.
    1. Can it be a warm LED?
    2. Does it need to be a grow light bulb or just a normal LED bulb would work?

    • greensunshine Post authorReply

      Hi Maiga! Get the highest wattage 3000/4000K LED you can and it will work out for you!

  21. matthew Reply

    Thanks for the article. Im looking at installing lights in a glass house growing tomatoes and wondering if you had a recommendation for lights to use and number of lights required

  22. Christian Reply

    I love this article. Keep returning to it for knowledge and info.

    I´m planning on planting vertical hydrophonic strawberries in my garage year round (extreeme sales prices in Denmark off season)

    what kelvin would be best for use in the entire growth period? (from seedlings to mature and producing) i´m currently planning on around 3000k, and as mush lumen as possible price and space-wise. maybe LED strips.

  23. sharda Reply

    To technical for me but answer this please?

    I have 4′ led shop light 42 watts, 4000 lumens and 4000K color temp.

    Will this work to start vegetables from seeds so when they are grow I can start transplanting them outside as soon as the night temps are higher?


    • greensunshine Post authorReply

      That is a great shop light, grow your vegetables big then set them outside when the temps are brighter!

  24. Jaycee Reply

    Such a comprehensive piece, thank you for sharing the information.

    I had been thinking of creating my own set up with red and blue, now of course I’m reconsidering this arrangement, but would it be wrong/crazy to think of mixing up warm white, red and blue LEDS in a single grow station?

  25. Zipporah S Reply

    This article helped me a lot, I am beginner gardener and I’m starting my plants inside. I have 2 LED cool lights that are 5000K and then 2 LED warm lights that are 2000K. So I’m not sure how I should use those or how I should place them. I just want my plants to grow the best they can until I transplant them outside. However, thank for this helpful information !

    • davidm Reply

      For seed starters the 5000K cool lights would be great. Add in the additional 2000K if you you are keeping them inside until more mature state.

  26. ShishitoAddict Reply

    Hello! Thank you for the informative article and for the fact you reply to comments 2 years after 🙂

    I always assumed 6500k light included all needed wavelengths but as per your article, this is not the case. What a shock!

    I am limited to having only 2 hanging lights over my system, preferably T5s… I can probably get a pair of 4 tube fixtures… What mix of T5 lights should I put on each of them (3000K 4000k? 5000K? more?) if I just want to grow hot peppers indoors?

    Thanks again!
    – A shishito pepper addict.

    • davidm Reply

      For growing hot peppers, I would recommend a mix of 3000K and 4000K for a good growth throughout the grow cycle.

  27. Brittany Reply

    Hi and thanks for such a thorough, helpful article. I’m confused though .. most comments are asking for suggestions on what K temps are best to buy for this or that project and I see in your responses you answer with specific recommendations .. but isn’t the main point of the article about how K temperature isn’t really all that relevant to growth? I’m now more confused than before lol .. please help! thanks in advance:)

  28. Michael Salotto Reply

    Thanks for this excellent article! It presents as being based in solid science and reality. It really helped me gain a better understanding of light and how it applies to growing plants.

  29. Jonathan Reply

    Would it be best to get a mix of 4000k, 3000k, and maybe even a designated grow led bulb? Because I have room for 6 bulbs, should they all be the same or would you recommend having 2 or 3 different kinds of bulbs, or does it not matter?

  30. Amy Reply

    There is a ton of information here and I need more help! I have succulents and they are all losing color. Will getting a LED light restore their color? And can you recommend which one to use specifically? I am mostly inside right now due to the Chicago weather.
    Thank you so much

    • davidm Reply

      Hey Amy,

      Yes succulents will start to lose their color and turn green without enough light. Adding some supplemental lighting should help perk them back up to health. Fortunately Spring is just around the corner!


  31. Jonathan Reply

    I am new to plant growing and I am trying out vertical hydroponics. I purchased a light fixture that has 6 sockets 4-5 inches apart spanning about 4 feet. I will have this standing upright (not hanging) pointing at my vertical tower. Because I have 6 sockets, I was wondering if you would recommend several different types of led bulbs to incorporate the red, blue, and white light, each bulb with a different spectrum. Maybe a couple 4,000k, and 5,000k but also lower around 2,000k? What would you recommend so that I can buy “normal” leds instead of much more expensive grow light leds? Thank you!

    • greensunshine Post authorReply

      Hi Jonathan, Nice project. 4000K – 3000K is a good idea!

  32. John T. Reply

    Thank you for educating me. I was convinced I needed 6500 K. I’ve been using 4 foot fluorescents (4000K) for years and wanted to upgrade to LEDs. I now realize when I upgrade to LED the higher temps are unnecessary. I’m typically only starting bedding plants for transplanting when the weather permits in MN. Your comments about infrared intrigued me. I have a heat lamp that I assume produces infrared energy. Should I try and incorporate that in my grow center?

    • greensunshine Post authorReply

      Hi John! Yes 4000k-2700K are great for LEDs. We create LED lights called the Electric Sky that contain high amounts of red and infrared light.

  33. Elle Reply

    When you say 4000K is good all around for veg to flower, is that specifically LED grow lights or would regular 4000K LEDs work?

    • davidm Reply

      Any 4000k LED would work, LED grow lights typically just run at a higher wattage.

  34. Mark Reply

    Hi Dan I’m glad to find such an informative article on the very confusing (at least to me) topic of indoor plant lighting. Most of your discussion centers around LED lights. Do CFL bulbs pretty much fall into the same “color” categories? ie: if a 3000k LED is a nice “all purpose light”, then is a 3000k CFL going to be similar?

    I’m trying to grow cacti and succulents (which prefer a lot of light energy) in a 4′ x 8′ space with a max height of 5′. Do you think 4 of the LED tubes (1800 lumens x 4 = 7,200 lumens) at 2700K be sufficient? Or should I add 4 or more of the 800 lumen CFL bulbs as well, perhaps in various kelvin values?

    Thanks for a great abstract, and for your advice.

  35. Kelly Reply

    Hi thank you very much for this article. It has been hard for me to find info on colour temp that doesn’t just apply to salvia plants!! I work in the film industry and have access to a lot of LED Tape. My first attempt at using it as a grow light did go very poorly. I ended up with very stunted plants. The LED tape that I have has a very high CRI of 95+ so some of this information doesn’t fully apply to the product I am trying to use. I have both bi colour tape (alternating warm Aka tungsten and cool Aka daylight diodes) that I can mix to any degree (between 2800-6500) as well as I have RBGW tape…. Maybe that would be better to use? Blending the white light with some red? Any tips for my next experiment starting soon?

    • greensunshine Post authorReply

      Hi Kelly, exciting project! If you ended up with stunted growth, likely due to not enough light, so adding even more white LED strips would help!

  36. Renuka Chandrasena Reply

    Hi, I am a starter. I am trying to germinate some tropical vegetable seeds in my green house (medium size)
    What range of Lumen and Kelvin is good for this.
    I do germination in a small area.

  37. Ken Reply

    Sansi’s latest grow light bulbs have a colour temperature of 4400K. Would that be suitable for a full cycle grow from start to finish?

  38. Leo Reply


    I’m very new to indoor plants and what not. Recently, I was gifted Bonsai tree seeds for a Dwarf Juniper tree. I have a very large Light Therapy light rated at 3500K. Can I use this to grow the small Bonsai plant?



    • davidm Reply

      The 3500K would work but you probably won’t have enough wattage.

      Thanks, David

  39. Calum Reply

    Taotronics full spectrum LED grow bulbs have a colour temperature of 1900K. Is this suitable for both veg and flower stages. Thanks

    • greensunshine Post authorReply

      Likely would want to stock with 2700K for balance growth!

  40. Phil Rubenzer Reply

    As an ex-chemist and budding indoor plant fan, I was amazed at the rapid phototaxtic response my philodendrons had to 5000 K LED bulbs, compared to the 5000K CFL bulbs I had been using for years. I saw more phototaxis with the 5000K LED bulbs in one week than I had seen with the 5000K CFL lights in two years! I am still in the early testing days, but the same plats are reacting more strongly to 6500K LED lights, about 1.5X more phototaxis. I would have never guessed such a rapid response, I thought the Kelvin temp determined it all, but with the lowering price of LED lights, I decided to try some. Wow! I have some very happy philodendrons now!

  41. Marcella E Phelps Reply

    I have a room 8′ long and 6′ wide. There is track lighting on the ceiling the length of the room. From the track lighting hang six sockets that each hold 120v 250w E26/E27 heat lamp bulbs. I typically use the room as a near infrared sauna. However, during the spring I’d like to use it as a grow room for vegetable seedling in preparation for spring planting.

    Would six LED bulbs around 3,000k each work as grow lights? If this would work, what watt should each bulb be and what lumen? Also would 2′ above the seedlings be a good height to hang the bulbs?

    If LED bulbs would not work for this set up, can you suggest bulbs that would work? I don’t want to go to the expense of buying and building a tiered grow wrack if I can use the space I have.

    • greensunshine Post authorReply

      Hi Marcella, I would say that if you’re just looking for seedling then yes bulbs could work, however that is quite a large space to only cover with 6 bulbs. Most bulbs are 8w of total power, and you would likely need ~200-400W of total LED power to run in that space, so look for a dedicated grow light.

  42. Debbie Reply

    Article is very helpful! I would like to learn more about light meters for LED lights. I and a friend of mine grow orchids. She has a greenhouse, and I have the LED’s. We are having trouble finding a GOOD, ACCURATE, meter. Does anyone have any suggestions?

  43. Harley Cullen Reply

    For the first time in history, the manufacturer is very truthful. To top it off, they are helping you (the customer) make an informed opinion! You have my vote!

  44. Amy Carraway Reply

    I’m wondering what you would recommend for milkweed, from seeds to planting stage? Thanks and keep up the great work!

  45. Phil Reply

    What’s missing from your argument is how far to synthesis actually works:

    Electromagnetic oscillations [light] excite electrons (in two stages) to such a high level that, using phosphorus (ATP) as a catalyst, Water is Split into hydrogen ions and oxygen ions.
    NOTE: Very similar to how a microwave works by exciting electrons with electromagnetic OSCILLATIONS

    The oxygen is released as O2 and the Hydrogen ions bond with oxygen on CO2 where the Hydrogens electrons have been “pumped” to, producing Glucose and Water
    12H2O +6O2 + Sunlight = C6H12O6 (Glucose) + 6O2 +6H2O

    The net equation is often given for primary studies: 6H2O + 6CO2 +Sunlight =C6H12O6 +6O2

    HIGHER FREQUENCY = Blue carries more energy
    LOWER FREQUENCY = Red penetrates further

    In Nature photo period flowers EG Blue Bells respond to far-red frequencies which penetrate the canopy as the spring leaves develop on the trees above them.

    Trees at the top of the canopy stay compact when they receive high levels of Blue light, an evolutionary response that stops them stretching too far and getting broken in the wind by staying not much higher than the rest of the forest.

    NOT: The trees that have reached the top of the canopy and become sturdy and compact Have Not become stunted.

    Secondly: High EC ( high nutrients) also results in compact plants.

    Growers have to be careful not to put the EC too high too much nutrients because if it is higher than the EC level inside the plant it will “burn” the plants which is when when water is drawn out of the plant.

    If you notice your plants have signs of nitrogen burn on the Leaves the nutrient level is much too high.

    In conclusion plants respond world to a high level of electromagnetic oscillations and a high level of nutrition but be careful not to burn them!

  46. Kees Reply

    Hi Dan, thank you for the great blog posts and taking the time to answer all these individual questions. It has been very helpful. I’m new to growing plants under artificial light and want to start experimenting with cloning and growing philodendrons, (low light tropical plants), with 30w, 3000k SMD-LED-spotlights this winter. They are 2700 lumen, though I understand this value does not say a lot. Do you have any recommendations as to how much lights to use and at what distance to place them from the plants? Thanks.

    • greensunshine Post authorReply

      Try to start at 3 feet! And see how low you can get while the plants are responding well, adjust a few inches per day.

  47. Gavin Reply

    What would be the most optimal kelvin for everything? Growing peppers and lettuce. Maybe some microgreens?

  48. Tom Reply

    I thank you for a common sense article also I found something that reduces the cost too at Walmart of all places I found T8 / T12 LED bulbs (Tubes) 48″ for $8.88 in a 2 pack (32/40 watt equivalent, G13 base, Soft white (2700k),
    Brightness: 1800 lumens).
    Which mean you can use the inexpensive florescent shop light fixtures. Up until now they were charging around $20 for a conversion set up per tube and they were something like 46 in long. Now Great Value claims they will last up to 44 years (Which I doubt) if they last 5 years that would be great I am still getting my money’s worth out of them. Another thing is I do not need to call out the Hazmat team if I break one. 🙂 Also what I do like about LED as compared to HPS is the amount of power the HPS use I do not need to take out a loan to pay the power bill.
    I see that some people are going 18 Hours on the lighting at the moment I have my timer set for 12 Hours should I extend the time?
    Also I have not seen many article addressing heating and I live in Colorado and the winter a fall night do get chilly any recommendations as I am in the process of converting an old travel trailer into a grow room (on a shoe string).

    • greensunshine Post authorReply

      18 hours is great for any vegetative growth since your plants will be getting more light! 🙂

  49. Shaun Reply

    Howzit GreenSunshine,

    A Very nicely constructed and well reasoned argument on a challenging topic.

    What would be your pick in terms of Kelvins if you were growing under Fluorescent?


  50. Mary Reply

    I bought a tropical plant at Costco because it was beautiful and I could not resist. I live in Seattle and I placed it near the window, but It doesn’t seem to get as much sunlight as I’d hoped. I am very concerned about it’s survival. However, I am too cheap to buy grow lights for this. Will it survive if I supplement it’s light with a desk lamp pointed at it and turned on in the evening hours? If so, would a LED 4000k or 3000k spectrum be best? Any advice? Thank you!

    • greensunshine Post authorReply

      Hi Mary, thanks for the question. I would probably get something a little brighter than a desk lamp, most likely look for one of those spotlight flood bulbs that are designed for the outdoors. Those will have a lens on it that focuses the light which is important if you’re only illuminating one plant. Shoot for 2000K-3000K but a 4000K would be fine. Best of luck!

  51. Manouche Reply

    I’m using 2700K in my 20l nano aquarium. All the plants are happy and they doing great photosynthesis. I used to use 6500k before and there was a lot of algea problem. At the same time the plants were growing very slowly. After 2700k Algae is no longer a problem for the tank and plants are growing quite healthy. Now I’m going to try to mix it with 3500K and 4500K leds together for the “bonus”. Thank you so much for the great information.

  52. Noam Reply

    Thanks for this very informative article!!
    So when looking at the charts and while looking to “fill” the most spectrum area, I was thinking what would be the outcome when having warm and cool at the same time?
    My thoughts are that would give a better coverage, spectrum wise, as each has different peaks.

    • greensunshine Post authorReply

      Hi Noam, Many LED lights use both warm and cool at the same time for this reason!

  53. Roumen Reply

    One of the best articles I have read on how plants absorb light. And trust me when I say I have read tonnes to try figure out what the best Kelvin is from start to finish. Most people say either 3000K or 4000K so I think I will buy the 3500K and be right smack bang in the middle! What do you think Greensunshine?

  54. Aspiring Greenthumb Reply

    Why do so many growers swear by 6500k lighting for the veg stage and 2500k for the flowering stage?
    You’re saying that if I want maximum yields all I need to do is use 4000k lighting for the entire grow? That certainly makes everything easier.

    • greensunshine Post authorReply

      Hi there — Yes. I would use 3000K for veg through flower of growth!

  55. Allen Ashby Reply

    Won Dan,
    This info on LED light spectrum was very well done, and very informative on light spectrums,
    I’am so glad I purchased these ES 300
    I can’t wait to get.
    Dan your huge help to all us with our our new ventures in this grow tent industries,

  56. Paul Reply

    It looks like a 3 light system. 1 at 4.5k, 1 at 5.5k, 1 at 6.5k would be the most efficient. I’m curious whether a pulsating light would be better than a steady on light. Any thoughts on this?

    • greensunshine Post authorReply

      Pulsating would just average out all the spectrums :). 4K is a decent all around spectrum.

  57. Steven McCabe Reply

    Very informative and definitely a completely different way of thinking about lighting than most LED companies will give you. Everything else I’ve read either touts red and blue light with virtually no other colors or warm white for flower and cool white for vegging.

    I think the only mention of ratio I’ve seen is the 5:1 ratio of red to blue that plants supposedly find ideal. Green/ yellow and far red are never mentioned.

  58. Ryan Reply

    I bought the 180 about a month ago. I spent a few months studying spectrums and the emerson effect.and finally decided i would just build my own out of 2, 7 paw adapters and assorted bulbs. Then i happened across your lights. I won’t even get to use it until Illinois comes through but i’m still thrilled with it because i understand it. In the meantime I’m gonna run a 7 paw with 6500k and 2700k bulbs with the covers removed. I love what you built. can’t wait to use it.

  59. Vlad Reply

    This is by far the most comprehensive article I’ve found on this topic. Although it’s best trying things out for yourself and see what happens, I’m scared to try this this year because I’ll have a very late start if I mess up the plants. Any advice on what’s the best solution for growing under normal leds? I have 4000 K ones, should I buy 2 6000 K ones hoping that they’ll average out and have the colours needed to grow?

    • greensunshine Post authorReply

      Hey Vlad,

      Should be good to go with 4000K all the way for all stages of growth!


  60. RLF Reply

    I suggest people try for themselves instead of reading and believing. I was amazed at the seedling differences for the ones under the daylight vs the warm light. They grew healthier under the warmer light. (under 3500K) so there is definitely a difference for seedlings. The ones under the daylight 5K were stunted

    • greensunshine Post authorReply

      Love to hear it RLF — thanks for the comment 🙂

  61. Daniel Reply

    I’m so happy we have smart people like you to figure these things out. I’ll stick to my dirt and organic nukes haven’t had much time into it but if I’m doing this good this fast. Now I need to tweak their environment and people will think I’ve been growing all my life. Just need a little help with the lighting

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