Let’s Pretend it’s Science!
I’ve built a number of my own LED grow lights, trying out a number of different styles and designs, I’ve also bought a few from China via Ebay. Leaving aside for the moment why I chose the style of system I’ve used (3 Watt emitters) there is one question that appears common and affects all types of LED grow lamps – colour (color) temperature and mixture. In the process of trying to best understand what works and why I’ve read a lot of different papers, a number of them contradictory and some just plain wrong.
I’m not attempting to set myself up as the expert, I don’t have the background nor the facilities to to turn this into real Science but I have put together an experiment that I think will be interesting to anyone who wants to grow with LED lights.
To begin, for clarity I use the term emitter to refer to the individual LED chip, an LED light uses multiple emitters. To make things slightly more complicated there are two basic types of LED emitters. Single colour emitters produce a fairly narrow band of light with a very pronounced peak at a specific wavelength these wavelengths are in the range of 20nm wide. The other basic type are “full spectrum” emitters that use a blue, narrow band emitter, to energize a phosphor much like that found in a fluorescent light. The “full spectrum” spans roughly 300nm and the individual phosphors can be tailored, most are some version of white but there are “grow” types available, all of them however produce “extra” blue light from the original emitter.
What I’ve attempted to do is set up 6 different “lights” using 9 emitters each, the different lights attempt to represent the most common commercial and or home build patterns.
I started twelve seeds of a lettuce variety called Merlot on January 14 2017 on the 26th I chose the six closest to the same size and moved them to net pots and placed them in the 10 gallon Rubbermaid DWC container.
When grown outside in natural light the plants resemble this picture. The photo is from West Coast Seeds the vendor and used without their knowledge or permission.
The lights are positioned 16 inches over the tops of the plants, and are set for a 12 hour day. The plants are in identically sized compartments and isolated from contamination by outside light by wrapping the whole thing with panda film.
The nutrients in the container are Botanicare PureBlend Grow mixed at approximately 1/2 strength.
THE LIGHT ITSELF
Beginning in the upper left an moving clockwise…
The first light closely mirrors the 9:1 Red:Blue ratio found in many of the inexpensive currently available Chinese LED grow lights. These are sometimes referred to as Veg/Bloom lights partially because higher levels of red light are associated with flowering.
4 = 660nm Red 2 = 640nm Red 2 = 620nm Red 1 = 450nm Blue
The second light, with a Red:Blue ratio of 2:1 is closer to the 4.5:1 ratio of an older Chinese made light I have. I have exaggerated the Red:Blue ratio to see what the effect may be.
2 = 660nm Red 2 = 640nm Red 2 = 620nm Red
1 = 450nm Blue 1 = 465nm Blue 1 = 475nm Blue
The third light is something of an experiment for me, all nine emitters are a new “GROW” type, the manufacturer claims a spectral output designed specifically for growing and a range between 380nm to 820nm.
The fourth light is made up of 6 of the above mentioned Grow emitters augmented by 3 Red emitters.
6 = Grow 2 = 660nm Red 1 = 640nm Red
The fifth light represents a fairly common home build style where Daylight or Cool White emitters are paired with supplemental Red emitters. In this case I used a 2:1 White:Red ratio. Similar to the fourth light except the Grow emitters were changed to Cool White.
6 = Cool White 2 = 660nm Red 1 = 640nm Red
The sixth light is entirely made up of Cool White emitters, these are by far the easiest and cheapest emitters to access.
Day one under the lights, panda film removed for the photo.
Limitations: (or some of the many reasons why this isn’t really science)
For this to be really scientific I would have had to produce many more than just the one plant under each type of light. I also should have used clones from a single parent plant to eliminate any genetic differences. The biggest drawback though is that I’ve only got 9 emitters per light this limits the number of lighting options available, many of the commercially available grow lights use more bands of light than even the 6 used in light number 2 (often 7-9), I’ve been using 12 bands for the lamps I build for myself.
I will be providing updated photos as growth progresses.
As a follow-up to this experiment I may grow dwarf tomatoes either under the same light or one configured to use 12 or 18 emitters.