At Future Eden we often get asked for advice on the ratios of different colour LEDs for use in grow lights. Anyone reading this will have probably realised the internet is saturated with a huge amount of conflicting information on the subject. Given the number of variables involved when manufacturing growing environments finding an ‘all-purpose’ answer to these questions is obviously going to be impossible. In this respect the situation is perhaps not that surprising, however, it’s certainly not helpful.
However, despite this, there are some generally accepted and easily demonstrable concepts that hold true for growing most plants commonly grown under lights. So, to help you avoid spending hours wading through poorly informed dross we have created this little guide to some of the basic principles of LED grow light design.
In order to begin considering grow light design, we need to take a step back and revisit your school Biology class and briefly consider the process of Photosynthesis.
The Basic Mechanics of Photosynthesis in Plants
At its simplest level Photosynthesis in plants the conversion of light energy into chemical energy which can then be used as a source of fuel for the plant growth and general existence.
At a chemical level, there are many complex reactions taking place for this process to occur, however, for simplicity sake, you can consider a plant as simply utilising light energy along with water and carbon dioxide to produce carbohydrates (fuel) and Oxygen as a by-product.
6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O
When designing a grow light, you are simply replacing the sun as a source of light energy. Providing there is enough light energy, enough water and enough Co2 present photosynthesis will happen. Great!
Replace the Sun – Job Done (not quite)
OK so for the plant to exist you just need to replace the sun at an appropriate level for the species and the plant will photosynthesise. So why all the confusion I hear everyone cry? Just use some Daylight White LEDs and you are there. It’s simple, no?
Well yes and no...
You certainly could use this product and it would work fine, indeed in some situations (such as living room grow light for instance), it might be desirable. However, in terms of the efficiency converting electrical energy into light energy that the plant can readily utilise, the daylight white LED is sub-optimal.
To understand the reasons for this we need to consider the process of photosynthesis once again…… sorry.
Chlorophyll – A, B and Carotenoids
Ok, so we have all heard of Chlorophyll – the pigment that absorbs light and allows Photosynthetic reactions to occur, provide fuel for the plants to exist.
However, what was not widely known is that Chlorophyll is formed of 2 types A and B. Whilst the chemical difference in these is not that important in terms in this overview of the subject, what is important is understanding that Chlorophyll molecules are better at absorbing light energy at different wavelengths of light. Or to put it another way, different colours of light are more readily absorbed by the Chlorophyll molecules.
Additionally, it is worth pointing out there is a third accessory pigment group called carotenoids. These pigments are not directly involved in photosynthesis rather pass the absorbed energy into Chlorophyll so are of importance however less so than Chlorophyll A and B. For the purposes of this article we will disregard these, and this shall be visited in more detail in a later post
In order to understand these optimal wavelengths, the diagram we have created the diagram below to aid your understanding.
A quick look at the above demonstrates that are clearly two rather massive peaks in the blue and red sides of the spectrum with a large valley in the middle around the green part of the spectrum. As such in a grow light you would be targeting these wavelengths to optimise efficiency in the design and get most ‘bang for your buck’ in terms of usable light energy. For information purposes, the measurement of the usable energy in a light source is referred to as PAR (Photosynthetic Active Radiation)
Now let us consider the daylight white LED (5500-6000k) LED example from before. If we look at the spectral power graph for this product we can there is a lot of energy concentrated in the green part of the spectrum which is largely reflected by plants (incidentally this is why we perceive lots of plants as green).
As a result, the usable light energy (PAR) of the daylight white product is actually quite low. In order to demonstrate this you can overlay the two graphs.
In this comparison it is pretty clear that whilst there is some correlation in the blue parts of the spectrum the majority of the Daylight White LED power is in the worst place in terms of PAR efficiency for Chlorophyll A an B. Hence this is typically why you don’t tend to use this type of LED in a grow light.
Wavelength Targeting: Increasing PAR
So, in order to create better efficiencies in design, you can now use LED technology to target specific wavelengths, thus increasing the amount of PAR (useable light) for the amount of electrical power consumed. This combined with the overall efficiencies offered by LED technology is the reason LED grow lights have overtaken old inefficient HPS and MHPS setups.
So which colours should I use?
Well in terms of product selection your design would be based on using single colour LEDs and/or cold or warm white LEDs. These combined in an array of your choice will allow for increased PAR. For simplicity sake, we have marked on the graph the specific products you might want to consider for the different peaks.
Typically, this wavelength targeting results in placing a lot of power in the red and blue spectrum ranges in varying ratios with additional smaller numbers hitting the secondary peaks. One side effect of this is that this creates a very garish pink light, so this may not be appropriate for living spaces. Here a combination of ice white and warm white LEDs perhaps with a full spectrum LED mixed in for good measure will increase the PAR whilst retaining something desirable for the home.
The Golden Ratio?!
Now given the massive number of possibilities with the numbers of LEDs and wavelengths options there is the question of the perfect ratio. Well, sadly there is no definitive answer to this question.
However, what you absolutely can do is to first understand what you are trying to achieve in terms of your design in relation to the species and a plant's life cycle.
Here there are some solid principles which should help guide the design from the outset.
Vegetative, Flowering or all-purpose grow light?
Certainly, one of the major considerations before you begin any grow light is to first define which period of the plant's lifecycle are you trying to cater for – Vegetative stage, Flowering stage or both?
In order to help with this, we have provided a description of the basic principles of these types of lights as it applies to light hungry summer flowering plants which should hold true for most growing situations:
Vegetative Stage – At its simplest, this is the early stage of a plants life from seedling to the commencement of flowering. In nature (for most light-hungry species) this equates to spring and early summer where the sun is higher in the sky and more of the shorter blue wavelengths get through the atmosphere. As a result, the pigments in plants have evolved to react better to blue wavelengths during this period. Thus, a blue dominant ratio light will help accelerate plant growth and also keep your plants short strong and stocky. The inclusion of the red wavelengths is still beneficial here however in a vegetative light the royal blue (440-450nm), bright blue (460-470nm) and often ice white (9000-15000k) LEDs are dominant.
Flowering – Conversely at the end of summer the sun sits lower in the sky and the atmosphere scatters less red causing a greater focus in the longer wavelengths of the spectrum. Hence light hungry species tend to flower and fruit better underneath a redder dominant light. In terms of design, this simply equates to have a greater ratio of deep red (660nm) and bright red (630nm) wavelengths in the design. The inclusion of blue wavelengths is still beneficial here but in a typical flowering light red LEDs are dominant.
It is worth pointing out here that 660nm is definitely the most important LED to choose and should form the focus of power with a few 630nm bright red LEDs picking up the lower peaks. Also, the addition of a small amount of 740nm Infra-red in the design has been shown to aid the onset of flowering and has been shown to increase photosynthesis – something often referred to as the Emerson effect.
All-purpose – Of course having separate lights for different stages is of course not always possible so a happy medium that covers both vegetative and flowering stage is often desirable. In such a light the ratio of both red and blue in less extreme. However typically, indoor horticulture is aiming ultimately for cropping and fruit production so typically these lights would still be a red dominant to help improve yield.
Interestingly the full spectrum PAR product now makes this very easy as its specialist coatings allow for all the relevant spectrums for an all-purpose grow light to be targeted in one product. This is often an easy way to jump into a project without needing to worry about ratio selection at all.
So, once you have decided on the project goals you can start looking at the finer details of the design using resources such as the information we have provided above, the spectral power graphs we publish as standard with all our products and other DIY build information of which there is a lot of information online. Then, use this information specific to your own application. This will ultimately feed a more informed project and better design decisions.
In choosing to build your own grow light you will be stepping onto the path of ultimate control, customisation and optimisation of growing environment. Not only will you understand the process of plants and internal growing processes better it is also an enjoyable way to get the best out of your build.
Of course, at Future Eden we are happy to assist in any way we can with our highly knowledgeable UK staff always available to answer any questions you may have.
Stay tuned for the second section of this guide when we will look at other chemical involved in the photosynthetic process and how these can be targeted using LED technology.
Thanks for reading!