Layers of efficacy in agricultural lighting
Greenhouses and indoor growing facilities which use technological and precision farming techniques to grow food and cannabis are heavy energy consumers.
In California, for example, power consumption for cannabis growing facilities accounts for 3% of the state’s total power consumption. In Denver, Colorado it is closer to 4%.
For a grower and farm owner, energy is a sensitive point that justifies deeper study in order to find how to maximize its use.
In a growing facility that uses artificial photosynthetic lighting, the agronomic lighting and HVAC systems are the two biggest energy users.
In order to maximize the abilities of the agronomic lighting array, we must check efficacy and make sure that for every watt of electricity we invest in, we manage to produce maximum biomass with minimal expense.
Efficacy is a subject that appears in many stages and places in our project. We call this “layers of efficacy or efficiency”. It is worth looking at them in your facility to check if they can be made more efficient.
Light planning equals energy. Your best chance at achieving the maximum from the lighting array is through forward thought, rigorous planning and understanding.
In the facility planning stage, it is advisable to create a lighting plan which can test the lighting array by simulating and testing different placement, outputs, power consumption and lighting angles.
Correct light planning will produce optimal placement of chosen lighting fixtures with minimal electric output in order to produce the lighting effect you are looking for.
By photometry I refer to the light beam created by the lighting fixture.
One of the advantages of LED technology is the ability to design the light beam. The law of physics states: the smaller the light source, the easier it is to influence the light beam. Lenses mounted on the LED do a good job, however it's important to remember that the addition of a lens lowers efficacy, and to pay attention to materials used and their quality. The lens itself has a light loss factor which should be taken into account.
Regarding this point, lighting greenhouses or indoor facilities with standard shelving, is very different from architectural lighting with regard to the space to be lighted which has a limited number of different sizes. A greenhouse will usually be a rectangle of 6.4m, 8m or 9.6m and gutter height of 3m, 4m or 5m. These numbers cover the majority of the situations that an agricultural lighting planner may encounter and allows lens manufacturers for LED to design lenses which will provide light beams giving uniform coverage of the typical areas we wish to illuminate. By a combination of a relatively small number of lenses, we can create an optimal light effect with minimum fading at the edges.
If the previous point talks about the advantage planning can give to efficacy and efficiency, the point here is that LED photometry using lenses is a precise tool that can produce lighting fixtures capable of efficiently lighting standard spaces.
Light absorption curves of chlorophyll are known, and are an important component that leading manufactures take into consideration when designing agronomic light spectrums.
There is tension between agronomy and commercialism in spectrum design. The wavelength of the LED affects component cost and also the PPF it will give per $ of investment. However, the preference of the plant is to see light wavelengths in a specific ration to the remainder of the spectrum, which is saying that, for the plants, it doesn't help if specific wavelengths are dominant in a spectrum which will raise PPF or produce a cheaper product if the plant can't utilize it. So, one of the dilemmas a lighting fixture planner faces is between data that he can write in his technical specifications (marketing on a theoretical basis) and plant reaction to the PPF/W/g index which will go out to customers at the end of a growth cycle ( marketing on a result basis).
More PPF in the technical specification shows higher luminous efficacy which allows the manufacturer to charge a higher price for the light fixture. Along with this, the PPF/W/g is a difficult component to plan, as the final result is affected by many other factors in the growth protocol apart from the spectrum.
As I see it, this is one of the fields where knowledge is scattered. There is no accepted global standard and this leaves a big gap in an important parameter which is hard to examine without extensive experience and means of measurement.
µmol/J or µmol/W.
How many light units will I get for each unit of energy/electricity I have invested?
This is not a difficult parameter to understand. It should appear in the technical specifications you receive and is worth a ton of money. Even if the light fixture is more expensive because of high luminous efficacy, in the majority of cases it is a worthwhile investment as it returns the extra cost in a relative short time. In really good cases we find that, when purchasing, the selection of expensive light fixtures with higher luminous efficacy will be more cost effective. This allows us to purchase fewer light fixtures at the same wattage than from a lower efficacy competitor’s products. The choice between alternatives needs to be based on cost per square meter or µmol/m2/sec of the lighting array in the facility and not by unit price of light fixtures.
Three points about this:
At the end of all this, the results will be examined and the question asked: what do we look at in order to test and select the best array for our purpose. I feel we should look in two directions:
In a precision agricultural facility the lighting array is one of the most expensive systems to buy and operate. It is also the component in the growing system that has the biggest influence on the growth results. In order to purchase an array with maximum efficiency in all 4 levels of efficacy, you need to choose people who know what they are doing.
Look for a person who can lead the lighting field, someone you know will bring knowledge in light planning, understanding of photometry, spectrum effects and efficiency of electronic components. In the long run, this is worth a lot of money.
I like to end my articles with one last complication which leaves space for thought and discussion.
With the development of the LED and possibilities of precise design of spectrums, lighting today is more than an engine for photosynthesis. Lighting in precision agricultural facilities producing food and cannabis is a growing tool which can be altered to affect taste, scent and morphology, composition of active ingredients, treating pests, disease and more. When we add these features to our agricultural lighting array, to achieve other important effects, we directly affect its efficiency. This is necessary and worthwhile; however I always prefer to make changes from understanding and in depth thought of all the connotations, for making the correct choice for the specific growing facility.
In depth, precise reference to power consumption and the continuous process of improving the efficiency of the agronomic lighting array will directly affect the profitability of each gram which is produced in our growing facility, and no less important is the minimization of the facility's carbon footprint and, in the end, of all the precision agricultural facilities.
My wish is for all of us to get the maximum from every resource we invest in, work, agriculture and life in general.