Why does energy efficiency matter when selecting LED grow lights?

Why does energy efficiency matter when selecting LED grow lights?

Why does energy efficiency matter when selecting LED grow lights? 150 150 Stein

Learn the 3 things to consider when choosing energy efficient lighting in your greenhouse or vertical farm.

Before we get started, let’s set some ground rules for this article.  

  1. I want to believe that everyone wants to do what’s right for the planet as long as they think their business can afford it, so we will not focus on energy efficiency and its impact on sustainability.
  2. In this article I will not post the name of suppliers or the price of the lights.  The price of the light will definitely impact people’s decisions and will vary widely based on the volume of lights being purchased and the supplier providing it.
  3. This article is not about light quality or light spectrum.  To look for information on spectrum please link to this article: Why I Still Believe in Red/Blue LED Grow Lights
  4. This article is written with commercial greenhouse produce growers in mind, but we do include a model which shows high output led grow lights running for long hours per day which could imply a greenhouse cannabis crop.
  5. We are fully aware that when you change the amount of energy going into the light as well as the type of electric light (HPS vs LED) one is using, it will have an impact on the climate in the growing/production area.  Factors like heat and relative humidity would need to be taken into consideration if one was taking a holistic approach to energy savings on the farm.

There is a growing amount of discussion around the environmental sustainability of a greenhouse or a vertical farm.  Much of this discussion is being driven by two or three big energy hogs inside these production facilities.  This includes the grow lights and climate management equipment like heaters and cooling units. 

We all know that LED grow lights are more efficient than the older HPS lights that growers have used for decades, but do we know just exactly how to measure that?  And do we understand how that will have a direct impact on not only energy savings but the operational cost at the farm?  For those growing in a greenhouse, understanding these numbers during dark winter months can have a huge impact on electricity bills.

3 FOCUS POINTS

  1.  Start by understanding the amount of light you need.  Urban Ag News recommends going to websites like Suntracker or the ESRI DLI maps site.  These websites allow anyone to determine the historical DLI monthly averages for their individual locations.  For this example I am going to use the area where my grandparents farm is located in southwestern Michigan.  As one can see this is an area of the United States that has very dark winters.
  2. Work with a trusted advisor or extension specialist to determine the amount of hours your crop needs to grow consistently year round.  Remember not all crops have the same light requirements and some crops have very specific photoperiods which can determine the amount of hours one can light their crops.  Use all of this information to see when you will need supplemental light and how much light you will need to supplement with.  

For this example I am going to use 1 acre of greenhouse tomatoes in a glass greenhouse located in southwestern Michigan.

Month Outside Light Levels Light Loss due to Greenhouse Structure Estimated Light Levels Inside the Greenhouse Target Light Level (DLI) Required Supplemental Light Levels μmol/m2/s Need Installed Supplemental Light Levels – Top μmol/m2/s Hours of Supplemental Light – Top Average Monthly Light Levels with Supplemental Light Amount of Lights in the Greenhouse – HPS
Jan 8.62 25.00% 6.465 25 18.535 Light 250 18 22.665 400
Feb 12.8 25.00% 9.6 25 15.4 Light 250 18 25.8 400
March 24.6 25.00% 18.45 25 6.55 Light 250 8 25.65 400
April 32.5 25.00% 24.375 25 0.625 Light 250 4 27.975 400
May 38.44 25.00% 28.83 25 -3.83 Shade 250 0 28.83 400
June 43.19 25.00% 32.3925 25 -7.3925 Shade 250 0 32.3925 400
July 45.52 25.00% 34.14 25 -9.14 Shade 250 0 34.14 400
August 36.39 25.00% 27.2925 25 -2.2925 Shade 250 0 27.2925 400
September 29 25.00% 21.75 25 3.25 Light 250 4 25.35 400
October 17.9 25.00% 13.425 25 11.575 Light 250 14 26.025 400
November 11.62 25.00% 8.715 25 16.285 Light 250 18 24.915 400
December 6.97 25.00% 5.2275 25 19.7725 Light 250 18 21.4275 400
  1. Now let’s calculate how much it’s going to cost you to run the grow lights for the estimated hours you and your advisor determined were needed per year to get the desired yields.  
    • To provide a baseline, we started with traditional 1000w HPS lights which are highlighted in yellow.
    • Then we chose six different LED grow light fixtures.  Because the light spectrum has an impact on how efficiently the lights run, we chose three broad spectrum fixtures and three that are red and blue only.
    • Since HPS is the baseline, the final column labeled “savings” shows how much the total savings per year one would achieve when replacing traditional HPS with the latest LED grow light technology.
    •  We made a few important assumptions in this example.  First, the cost per kwh is around the USA national average of $0.09/kwh.  Second, the same amount of grow lights would be used even though there would be some relative differences in umols/m2/s measurements for two of the samples.  We decided not to change them because that would have an impact on uniformity (the even spread of the light over one’s entire crop) and associated capital cost not addressed in this article.
Specifications
Products Spectrum umols/s w umols/j cost per kwh hours per year to kwh cost per year No. of Fixtures Annual operating Cost
Baseline – 1000w DE HPS “FULL” 1800 1080 1.7 0.09 3082 3328.56 $299.57 400 $119,828.16
Specifications
Products Spectrum umols/s w umols/j cost per kwh hours per year to kwh cost per year No. of Fixtures Total Savings/Year
A White and Red 1900 613 3.1 0.09 3082 1889.266 $170.03 400 -$51,814.58
B Red and Blue 1900 528 3.6 0.09 3082 1627.296 $146.46 400 -$61,245.50
C White and Red 1800 520 3.5 0.09 3082 1602.64 $144.24 400 -$62,133.12
D Red and Blue 1900 520 3.7 0.09 3082 1602.64 $144.24 400 -$62,133.12
E White and Red 1680 620 2.7 0.09 3082 1910.84 $171.98 400 -$51,037.92
D Red and Blue 2330 620 3.8 0.09 3082 1910.84 $171.98 400 -$51,037.92

Running these simple calculations will show you why you need to look at energy efficient lighting and in general the importance of researching energy efficient equipment in general.  What these calculations do not show is the quality of some fixtures over others.  Buyers must always be aware of the value of warranties, ease of returns, durability and quality of product plus accuracy of your vendor to create detailed information on the best way to use and install fixtures.  We understand that this topic is intimidating for most, but this is a major purchase for your farm.  Make sure to take the time to learn the math and do your homework before purchasing.

Diving into these calculations will also highlight how much energy will be required to grow a wide variety of crops consistently with uniformed yields year round in climates with low light.  Hopefully in articles to come we can discuss what this means for our environment and how we might develop additional ways to lower that ecological footprint.

For help in calculating the energy efficiency of grow lights you are considering, please email us and we will connect you with professionals capable of helping you make an informed decision.


Chris Higgins is the founder of Urban Ag News, as well as General Manager and co-Owner of Hort Americas, LLC a wholesale supply company focused on all aspects of the horticultural industries. With over 20 years of commercial horticulture industry experience, Chris is dedicated to the horticulture and niche agriculture industries and is inspired by the current opportunities for continued innovation in the field of controlled environment agriculture. Message him here.

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