P. L. Light Systems: Maximize Yields with Smart Lighting Strategies. Using Metrics For a More Efficient Grow

Jillian Whitehead

Helpful Tools, Lighting Strategies, Return on Investment | July 29, 2020

There is a strong relationship between lighting and yield, as we know that with every 1% increase in light, there is a 1% increase in growth and yield.   Measuring yield in your greenhouse is an important way to measure efficiencies and profitability, so you can better assess how your inputs affect overall yield and plant growth.  

In this article, we are going to overview the relationship between lighting and yield and examine ways to calculate yield and manage your lighting system to be the most efficient and profitable for your growing operation. 

Growing in a controlled environment allows you to manipulate and optimize your environment to achieve the highest yields, as it allows you to not be controlled by the seasons. Using technology, such as lighting, environmental controls and automation software to better manage your environment, are ways to increase your efficiency. Heating, cooling, ventilation and CO2 enrichment are also important environmental considerations that will have an impact on the health and productivity of your crop, and should be considered as part of your overall evaluation of yield and productivity.   

Your Environment 

First off, having good production planning and process management will allow you to manage your environment easilyregardless of whether you’re growing in a fully controlled (indoor) or greenhouse environment. 

Working in a fully controlled environment such as a warehouse, can make it easier to manage climate controls compared to a traditional greenhouse, because you rely less on outside environmental parameters such as sunlight and outdoor weather conditions.  However, you must have your environmental controls dialed in, so you’re not wasting energy or space. When working in a warehouse, where artificial light is your only light source for plant growth, optimizing your environment is key to being profitable. 

In a greenhouse setting, where luminaires are used for supplemental lighting when light levels are low, to extend day length, or to reach desired DLI, making the right choices when it comes to selecting a luminaire is important for assessing overall ROIIn general, lighting operation costs are lower in a greenhouse because unlike warehouses, they do not need to be on all year since the sun provides the majority of the light.  The addition of supplemental lighting in a greenhouse, will improve photosynthesis, yield, product quality and enable earlier or year-round production. We highly recommend using a PAR (photosynthetic active radiation) sensor in a greenhouse setting to ensure your crop is getting a consistent level of light.  

Deciding what lighting is best your application is an important part of getting the best return on your investment

What Lighting Should I Use? 

There are several kinds of horticultural lighting used by growers (HID and/or LED luminaires), however determining what will get you the greatest return will depend on your application and overall goals.   

While spectrum influences morphology, it is light intensity that influences over yields on crops.  When deciding what lighting system to go with to maximize yields, spectrum is not necessarily as important as light intensity.  Although, having the appropriate spectrum for specific stages of growth will help to optimize overall efficiencies and target specific goals you may have 

So whendeciding between HID or LED lighting in terms of yield and profitability, it is more important to look at all the aspects within your growing operation and then decide if the ROI makes sense.  For instance, if you already have HID lighting, and want to go LED, installing a hybrid LED-HPS system might make the most sense instead of converting the entire operation over to LED, as it will help decrease overall costs since you can probably keep the existing infrastructure.   

Other considerations should include your regional climate.  If you are growing in a northern climate, that relies on HPS lamps to help heat the greenhouse in the winter, then an HID system would likely make the most sense so you can increase savings on heating.  If you are growing in closelytiered vertical operation in the desert, then LED luminaires would likely make the most sense for you because of their lack of radiant heat.  Again it will depend on your individual application, as no two facilities are the same. 

Another important consideration is how crop growthuniformity and productivity are influenced by the distribution of light and amount of light delivered to the crop canopy. If you have spaced benches, LED lighting might make more sense because of the directional distribution of light.  If you are growing with close benches, and little to no walkways, a HID or hybrid application might make more sense.  This is because LED and HID lighting are different in the way they direct light into the crop, and LEDs will require more lights in a grow space then HIDs to achieve the same uniformity – so this should also be taken into consideration. 

Many times, if light plans are not done correctly by a professional company, there can be areas of low and high intensity because uniformity was not properly calculated.  This will make for greater inefficiencies in your operation, as it will affect many areas including water management, pest/disease management, and some plants may grow slower and faster making it harder to manage the environment and ultimately your yield will suffer. Working with a professional lighting company such as P.L. Light Systems will help you achieve the greatest efficiencies in your facility. 

Maximize your efficiency with the right luminaire. Using Asymmetrical reflectors will help increase your light distribution on to the plants and avoid light being distributed where it’s not needed like onto walkways and walls.

Crop Type 

The type of crop you grow will also influence your lighting choice.  The top of the crop canopy will naturally receive more light than the bottom and directing light down into a tall crop can be difficult with the wrong luminaire.  For tall crops like tomatoes or cannabis, it’s important to think about how the light source is directing light into the crop – having a reflector will naturally increase the amount of light penetrating deep into the foliage.  Lighting which lacks reflectors, such as with LEDs, will require more luminaires to achieve high uniformity and even light distribution into the crop.  So choosing the correct lighting system is imperative for optimizing your environment and ensuring you have a good return on investment with a palatable back period.  


Determining your PPFD and DLI for your application: 

The target light level at the crop canopy should always be the starting point of a light plan, then all other factors that will affect the layout and performance of the luminaires should be considered to determine how to achieve the desired light level, with optimal uniformity and efficiency.  

Understanding how light is measured and the amount of light needed for your crop is the first step in optimizing your lighting system to get the most out of your crop.  We use two measurements to measure light: PPFD (photosynthetic photon flux density) and DLI (daily light integral). 

PPFD is a measurement of the amount of PAR (photosynthetically active radiation) that is distributed to, and arrives at, the crop canopy. PPFD is measured in micromoles per square meter per second (μmol/m2/s). It is important to note that PPFD is a ‘spot’ measurement on the crop canopy, it is important that the average PPFD at several ‘spots’ are taken under a defined height. 

Measuring your light levels with a light meter is recommended ensure you are hitting your DLI and maximizing your light output.

DLI refers to the cumulative amount of PAR light received in a 1 square meter (10.8 sq. ft.) area each day, or (mol/m2/d)Like measuring rainfall, DLI cannot be determined from an instantaneous reading. Just like a rain gauge is used to measure the total amount of rain that was received in an area during a 24-hour period, DLI measures the accumulation of PAR light over the course of a day. 

Knowing whether your crop requires medium, high or very high levels of light is important to determine your DLI and maximize your efficiencies and yields. A lower light crop like lettuce requires only 17 moles of light per day, but a high light crops like cannabis or tomatoes need at least 30 moles of light per day for proper growth and development, and to ensure the highest quality and yields.   For a crop like cannabis, some growers will even push the light levels to 40-45 moles per day, which helps them to increase yields. It is important to note that the higher the light intensity, the more you need to monitor other environmental parameters to ensure a balanced growing environment.   In addition, when it comes to cannabis there are many different strains that have been bred to respond differently to various temperatures, light intensity and other parameters.  If you can know your plant’s light requirements, this will help increase your success of growing at higher light intensities, since some will perform poorly under high light.   


How to Measure Yield 

Yield is the most important measurement of profitability. When growing in a controlled environment, understanding yield metrics is important to make sure you are getting the most out of your lighting – and to make sure you are being profitable.  As mentioned, the choice in supplemental lighting will depend on your type of facility, environment and crop.  Using supplemental lighting can allow for an increase in plant density, while still obtaining greater fruit production or yields. Crop growth, uniformity and productivity are influenced by the homogeneity of light distribution and amount of light delivered to the entire foliar canopy. 

The most common way to measure a crop like cannabis is in grams/kilograms per square footYield is seen as the most important way to measure potential profitability.   Measuring yield allows the grower to understand how well the space is being utilized, if grow conditions need to be adjusted, or if some varieties/strains produce better than others.  

To calculate this, you need to look at your cultivation space and area of plants.   

We will use cannabis as an example and measure yield in grams per square foot of growing space. 

If you have a 5000 square foot cultivation area that has 100 4×8 ft tables, your grow space would be about 3200 sq ft. 

If you reported a yield of 195000 grams from that space, you can now do your calculation. (Note: the final product weight should be reported dry and destemmed, as it should be in a condition which will qualify as a final product.) 


Total yield in Grams/Total cultivation area = grams per square foot 

195000/3200 = 60.94 grams per sq foot. 

As you can see, from that space you average about 61 grams.  To make this even more accurate, you should be measuring the yield in grams per square foot per year to get an overall average and better understanding of areas where you can improve.   

From this number you can now assess if you are reaching your goals, and if parameters should be adjusted.    You should also be asking yourself if the ROI makes sense, based off these yields. Are there areas to improve, such as increasing CO2, temperature, light levels, plant spacing, etc.?  

Grams per Light is another way to calculate yield, however, it is not the most telling of ways to determine if your space is efficient, since this measurement only tells us the yield under a single light. However, we also need to take into account the wattage of the lamp and the spacing of the lights to truly see how efficient it is.  Therefore, because it lacks specifics such as size of the space, and how many plants are “under” one light, it is not a recommended way of measuring yield or efficiency. 


Production Efficiency 

While crop yield is an important way to measure metrics for profitability, the amount of product a grower can produce, measured against the resources used to produce it, is a more holistic approach to measuring overall efficiency.  It’s important to maximize productivity per square foot the same way other types of industries do, without sacrificing efficiency.  The size and set up of your facility can account for overall efficiencies. With the use of environmental control systems, that can automatically control environmental parameters to have your facility running at its most efficient, will help streamline growing. Poor production management and planning will also lead to inefficiencies.    

There are numerous other factors that have an impact on a crop’s yield, including facility design, genetics, CO2, temperature and nutrientsEnsuring these are all in balance is important, because it can limit the efficiency in your operation. For example, if temperaturelight and CO2 levels are not balanced, your plant will not grow optimally, and you will have wasted energy.  Having an optimized environment will bring you the most success and will help you get the most out of your lighting a systemachieving the highest yields from your crop, without sacrificing plant health quality.