Experiment: Red Light vs Blue Light -How Spectrums Affect Plant Growth- LED vs CFL

Blue light vs Red light. Which is better for vegetative growth??? Instinctively, the answer might seem obvious: Blue light is for vege! That basic mantra is plastered all over the internet. But if the issue was so simple, then why are many LED grow lights are sold using such a large ratio of red to blue? Why don't we see many pure blue "vege" lights?

Wouldn't nurseries growing seedlings want all blue LEDs? Wouldn't indoor lettuce farms prefer all blue light since they don't want their lettuce to bloom (bolt)? Are horticulture LEDs high in red light because most of the artificial lighting market is targeting weed growers who want marijuana producing massive buds?

THE EXPERIMENT:

I decided to stop making assumptions and to test this for myself! Specifically, today's experiment tests the following HYPOTHESIS: Blue light fuels vegetative growth. Thus lettuce plants grown in the absence of blue light will grow slowly and develop less plant mass than lettuce grown under blue light.

I set up several grow chambers using 4 types of artificial light sources: Full Spectrum 6500k CFL, Pure Blue 450-460nm LED, Red/Blue 460+630+660nm LED and Pure Red 620-630nm LED. One hydroponic (Kratky's Method) lettuce was placed under each light.

QUICK CHARTS:
1:44 - Lights Specs for This Test
2:14 - Specs for Hydroponic Solution
7:27 - Final Results of Lettuce Growth
8:03 - Photosynthetic Absorption Spectrum
8:10 - Photosynthetically Active Radiation (PAR)
10:53 - Recommended Light Levels for Lettuce
12:02 - PPFD Light Readings for the Lights

This UPS power station can backup a grow light!

My Apogee Instruments PPFD Meter (# CommissionsEarned):

RESULTS:

It turns out that red light was able to grow just as much plant mass as blue light. An added advantage to red LED light was that it generated just as much PAR light, while consuming 29% less electricity.

The red light might have produced a large plant, but the plant quality was not desirable. The stem & leaf growth was very elongated. It was similar to a lettuce plant that is bolting. The leaves were pale, indicating low chlorophyll levels. They were very weak, easily separating from the stem.

The blue LED showed similar dry weight as the red, but it had higher chlorophyll levels, exhibiting a much greener color and stronger tissues. Growth was still undesirable tho, as the plant stretched vertically, rather than staying compact. It might appear that light levels were too low, but the PPFD PAR numbers were actually too high. Also, the blue light did not generate as much root mass.

Check these sources for appropriate PPFD levels for lettuce:

The Red / Blue LED resulted in a more natural, compact growth pattern. Clearly the lettuce plants require a mixed ratio of reds and blue in order trigger a compact growth characteristic.

PAR:

Many growers focus on chlorophyll A + B absorption charts, assuming that other wavelengths of light are useless to plants. However, PAR (Photosynthetically Active Radiation) spans the entire range of light between 400nm & 700nm. All of this light can fuel photosynthesis w/ varying degrees of efficiency. Additionally, photosynthesis is not the only concern of a grower.

PHOTOMORPHOGENESIS:

We must account for photomorphogenesis, which deals w/ the way plants grow in response to various wavelengths of light. This can even include wavelengths beyond the realm of PAR, such as UV light. Plants display various morphologies or developmental traits in response to combinations of light. A classic example is the ratio of red to far red light.

In this test, we saw that including blue light at a ratio of 1:3 (blue to red) was able to prevent the plant from growing in an elongated fashion. This photomorphogenic response explains why we see the popular red / blue mixture of LEDs that are so common in grow lights.

FINAL THOUGHTS:

Full spectrum light is the best way to ensure that plants are getting everything they need. But producing such light in LEDs can reduce efficiency. Red and blue LEDs are the colors that offer highest levels of efficacy. Their light is readily absorbable by chlorophyll and easily drives photosynthesis. In a proper ratio of blue to red, most plants respond with natural looking growth.

What about green light? Do plants use green light, or it wasted energy?
Find out at my site:

#ScienceExperiments #LEDGrowLights #VegetativeGrowth #IndoorGrowing #ArtificialLightings #HydroponicLettuce #UrbanGardening

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[Albopepper]

*LEARN MORE:*

This UPS power station can backup a grow light!

_Check out my LED grow light reviews:_

[RageKroc]

This video alone explains, with much clarity, just how much there is in only one facet (lighting) of growing plants. As a novice gardener I thank you for educating aspiring growers, it takes a special kind of of teacher to explain things clearly, and you certainly have that rare talent.

[supercow]

You're a great teacher and I like your tone of voice and inflection.

[boehrb]

+1000 bonus points to you sir for including a well-structured written summary in the video description 👍

[WorthyBuzz]

Wow great video! Takes a lot of work to plan an experiment, build the clambers, film, edit, narrate commentary, and upload it all for us to consume in a fraction of that time. Thank you on behalf of us all for such great work!

[editoons]

Thanks so much Albo Pepper! I bought a $50 full spectrum grow light on Amazon yesterday, and came today. Rated at 150v and 600w. It had two options, "VEG" and "BLOOM". VEG alone was red, and BLOOM was Blue-Purple. When I had it set to both it Was Purple. I didn't know how the different colors had impacted the plant, so I conducted research (for about 3 hours) and found your video. It was really helpful. The grow light i bought had a few cool white LEDs, and I think that would help with keeping the plant's green color (since white has all colors of the visible spectrum), and the rest was red, blue and purple leds. I've decided to use both settings after watching your video. Thanks very much again!

[timmyd]

Not gonna lie. This guy is super wholesome. Everything was explained perfectly using the scientific method. Perfect for literally anyone!

[JebGardener]

Wow! great video. Was the lettuce Black Seeded Simpson? I notice that seems to burn more in my setup and Romain is much more forgiving. Thanks!

[craigathonian]

Great experiment ! I remember researching what the Japanese came up with from their studies years similar. From my own, i found adding cold white LED's, (15000k) to the red and blue took care of the minor color needs of the plant....in effect, rounded out the plants diet. Thank for posting a great video !

[Dee--Jay]

i think as the plant grew, the light should also back off some distance

[sneekysmurf]

I feel like it’s a very informative “Blues Clues” version for a adults. Very well done

[dancoulson]

Never grown a plant in my life. But I did find this very interesting and informative.

[calebfinn]

Great video, way ahead of your time to be honest. Professor Bruce Bugbee is basically replicating your study at University of Utah right now in a more controlled and broader setup. Thanks so much!

[ittybittybias]

This is the only video on plant lights that has given me an idea of which colour light I should use for my plants. I've been researching for hours and I finally understand. Thank you so much for this practical demonstration!

[stupiduser]

I am 52. But at age 12 I did a science fair project on this. I used high intensity camera lights and colored gels for color.

[timyates]

Great vid with useful information. Thank you ive been indoor growin a long time 25+ yrs each day and have trouble finding non beginning level vids because even the people posting the vids are less than well informed or lack experience. When i do find one thats good or that has useful info i appreciate it ! Thanks

[dustinsmith]

I absolutely love your scientific approach to testing each. Measuring every variable possible. Excellent.

I think you should compare your red light plus your blue light(rather than the color changing ones) in comparison to the cfl. That''ll give you roughly the same wattage and give you an accurate test for red/blue.

Thanks for a great explanation.

[SW-zuve]

This video proves to me "grow lights" sold as such to gardeners are an idiotic waste of money. The only plant that didn't look like a mutated freak show was the CFL. Fast forward 3 years what is now a "normal" light bulb with a full spectrum color temperature even has "grow" on the labels. Its all I ever used and all I ever will use. Thanks for the info. You're content is great!

[Guitube]

Wow that is the kind of rigorous experiment I like, thanks ! I have a light bulb that I highly recommend, it's the GE 32W led full spectrum. The light is very similar to the sun (warm white), it's very powerful yet much less heat than CFL and I'm having great results !

[northstar]

Very good. Better than most info from grow light sellers