When a grower uses supplemental lighting in their greenhouses, the goal is to help their plants — annuals, perennials, produce and others — grow as healthily and as efficiently as possible. With the right amount of supplemental light, a grower can expand their growing season, growing 24/7 or, in some cases, speed up production time.

There, however, is a catch: Using supplemental lighting is not as simple as buying fixtures on the internet, installing them in the greenhouse and then reaping the rewards a few weeks later. With lighting, growers need to be mindful of how much photosynethically active radiation (PAR) is actually being provided by the fixtures. To do that, they need to measure their light, most commonly with a quantum light meter and/or light sensors.

“You're not going to be able to calculate your daily light integral (DLI) [with a handheld quantum light meter], but it's a good way of going into your greenhouse and seeing what the light intensity is when it's bright outside or what the light intensity is when it's cloudy,” says Dr. Roberto Lopez, an assistant professor and extension specialist at Michigan State University specializing in controlled environment specialty crop production. “Obviously, it's going to vary from day-to-day and from one season to the other. But at least it's going to give you kind of a snapshot of what your light levels are and whether you should be using supplemental lighting or whether you should be using your shade curtains.”

Light measurement options

Light meters are not a new technology — although Lopez says they have become more widely used by greenhouse growers over the past few years — and there are a number of options available to purchase, ranging in cost from a few hundred dollars to over $1,000. In Lopez’s opinion, there is one type of light meter growers should invest in because it measures the wavelengths of light that are utilized for photosynthesis.

“Having a light meter is important, but having a quantum meter is even more important,” he says. “A quantum meter is basically measuring the light that a plant perceives in the PAR range (400 to 700 nm) and that’s what we're most concerned with. If you have a foot candle meter, it is basically just measuring the light that we can see as humans and that's not what we are concerned with in this particular situation.”

Additionally, Lopez says that you need to do your homework and ensure the light meter you purchase is calibrated with the type of lights you are using in order to give you the most accurate readings possible. For example: If a grower has LED fixtures, but the meter is not calibrated for use with LEDs, their readings are going to be incorrect. The cost is higher for quantum sensors, but if growers want accurate readings, the extra cost is necessary, Lopez says.

There are also other ways to measure light in the greenhouse. One option is light sensors that can be paired with light meters to measure exact wavelengths and light intensity. According to Dave Johnson, a senior product manager at Li-Cor, there is also software growers can purchase to track different light measurements over time and give their readings context over months and years.

“Ultimately, in a greenhouse, you are trying to grow your plants most effectively, most efficiently as far as energy is concerned, as far as water is concerned,” Johnson says. “And so what you’re looking at, potentially, is figuring out that best way to do that with the light sources in your greenhouse.”

Best practices

Although Lopez says the cost of a light meter can be intimidating for some growers, he says it is a must for growers who have invested in supplemental lighting. It can also help inform future decisions about whether or not to add more lighting.

“Sometimes it may be under [what you expect],” Lopez says. “Sometimes it may be over. Over isn't necessarily a bad thing, but being able to go in at night when those lights are on and take your own measurements is quite important. Being able to determine what light intensity your fixtures are putting out, then you can use that to calculate your supplemental DLI and determine whether that light intensity is sufficient or if you’ll need to add more lights.”

Johnson says that having the ability to properly measure light is important for smaller greenhouse operations even though they may only have a few light fixtures in the greenhouse.

“I think it’s still important [for smaller growers],” he says. “The main thing driving growth is light. If you don't know what your light level is or don't have some kind of control on your light, you’re kind of at a disadvantage.”

Once a light meter is purchased, both Lopez and Johnson say the key is to actually use it. Lopez recommends taking measurements “as often as you can” — several times a week at minimum, especially if the greenhouse is not fitted with an automated environmental control system that manages the lights — and recording the readings. From there, a grower can determine if the lights are aiding plant growth or wasting energy, and what the next step should be.

“Use it,” Lopez says. “Don’t just have it on your desk.”

Abbottsford, British Columbia-based Van Belle Nursery uses technology to its advantage, implementing overhead irrigation, as well as drip irrigation when needed, and collecting water from rain, plants and irrigation. In its Colour-Retail Ready Division, Pablo Costa also controls the operation’s LED lights with sensors.

Costa, operations manager for the nursery’s Colour-Retail Ready Division, grows hydrangeas under LED lights in one, one-acre zone — out of 10 acres of total greenhouse space that is covered with double poly. He also performs trials with the LEDs on various annuals, perennials and succulents. “Definitely, in our location, we need supplemental light to have crops for early spring,” he says. “It’s essential to produce that crop and have early flowering.” If Van Belle Nursery didn’t use LEDs, Costa says, it could lose that early spring crop.

From January through around May, Costa runs the Philips Lighting-brand LEDs during the early morning and at night. This is to extend the amount of light the plants receive throughout a given day — or the daily light integral (DLI) — which, in the dead of winter, is sometimes only about eight hours of natural sun. This equals about two moles of light per day in January, Costa says, but hydrangeas need at least 12 moles per day. “[We use LEDs for] basically the DLI light program and also the hours,” Costa says. “I like to have at least 12 hours of light continuously, plus the light intensity.”

How LEDs help Van Belle Nursery

Van Belle Nursery needed supplemental lighting to achieve optimal development for early spring, and it implemented LEDs three years ago, in part, because of energy costs, Costa says. Although the initial investment is higher for LEDs than for high-pressure sodium (HPS) lights, LEDs are lower maintenance, last longer and do not give off the same amount of heat as HPS lights, Costa says.

Because the light intensity is low in Abbottsford, LED lighting aids in the production of most plants, Costa says. Van Belle Nursery works together with Dr. Abhay Thosar, senior plant specialist at Philips Lighting, to select the best light spectrum for each species of plant, Costa says. “What I noticed that is [by] using these purple lights — some colors, like red on the leaves or red on the flowers — [are] getting more intense,” he says.

In Costa’s experience, LED lighting often speeds up plant development and growth, and the plants develop more than they do under only natural light. He points out that light, along with water and fertilizer, are integral for plant growth. “It’s part of the triangle that the plants need,” he says. “If you have more and you are more under the requirements that the plants need, you are going to have better performance.”

Plants with red hues that Costa grows under LEDs, including many of the hydrangeas and annuals such as coleus, have stronger colors than those that he grows without LEDs, he says. “Also, the green color of the leaves is greener, so at some point, you need less spraying of micronutrients than we usually do, especially for the hydrangeas,” he says. “When you have [plants] under the lights, the color of the leaves is a little bit greener than the other ones, which are paler.”

With the added light, the plants also stretch less and are more compact, Costa says. “At the end, we use less PGRs, and we have the flowering on time,” he says.

Getting into a rhythm with LEDs

“I think we were one of the pioneers using LED lights for ornamental plants,” Costa says. Van Belle Nursery plans to continue performing research on the effects of LEDs on retail-ready plants, he says, and it is exploring the benefits of LEDs in young plant production.

In his three years of experience working with LEDs, Costa says he has become more accustomed to controlling the lights and taking measurements. “You have to look very closely to measure how your light intensity [is] outside, how your light intensity [is] inside — I change the poly on the greenhouse — so it’s continuous learning,” Costa says, adding that he needs to make preventative rather than reactive decisions.

Looking to the future, Costa says he sees Van Belle Nursery continuing to advance through the addition of LEDs. “I think it’s going to help that the price is going down in the investment, because it is a very high investment that you have to [make] right now,” he says. Costa predicts that the prices will probably still go down in the future, resulting in a faster ROI. “Now, it’s taking roughly five years to return the investment,” he says. “If [initial costs are] going to go lower than that, definitely, it’s going to help.”

When we conducted our first State of Lighting Report research back in 2016, we were interested in establishing a baseline for how and why ornamental and produce growers were — or weren’t — utilizing lighting in their operations. This year, we were able to compare the results of the 2016 report with our new results, which was an exciting prospect.

Overall, the demographics and numbers of respondents were similar in both reports, as were the approximate percentage of growers using some type of lighting, whether it was high-pressure sodium (HPS), light-emitting diodes (LED), or some other type — 37%. The three most popular reasons these growers use lighting in their operation were day length extension, supplemental lighting during low-light periods and propagation. Jessica Marlowe, propagation tech at North Carolina-based Hoffman Nursery, says that she’s noticed an increase in the use and research of lighting, especially for extending day length. “I worked in retail early in my career, and it used to be that you were limited to growing crops like poinsettias if you didn’t have the lights,” Marlowe says. “Shorter day length was a big limited factor.”

Professor and columnist Christopher J. Currey highlighted two significant changes that he’s seen in lighting over the years: “an increased awareness on the impact of light on horticultural crops” and “a refinement on the quality and value of lighting technologies.” That is to say, more growers understand the potential positive impact of adding light to their crops, and the available technology has advanced by leaps and bounds, whether it’s a higher efficiency, double-ended magnetic HPS or improved LEDs with variable spectrums and higher outputs. “I think the response to quantity of light is generally understood,” Currey says, but light quality and spectra are still being researched for potential benefits.

“[Over the past 20 years], I have seen a shift to far more efficient lighting systems, and I think we have moved away from the concept that more light is always better,” says Kyle Banas, nursery manager and head grower at Pizzo Native Plant Nursery in Illinois.

However, the biggest change that we noted was in the usage of LED lighting. In nearly every category, both ornamental and produce crops, from propagation through finishing, more growers are using LEDs. Duke Stockslager, owner of Stockslager’s Greenhouse & Garden Center near Dayton, Ohio, says that they have always used traditional, HPS or metal halide lighting in their operation, but that switching to LEDs has helped them to improve the quality and timing of their plants. It also was a key factor in their ability to become a rooting station for a well-known plant breeder, bringing in additional revenue.

For Lloyd Traven, the decision to incorporate LEDs into Peace Tree Farm’s Pennsylvania greenhouses has enabled them to grow and sell high-quality basil plants to a local grocery chain 52 weeks out of the year, and has improved their overall propagation quality. “We feel that [LED lighting] will revolutionize the way we grow here,” Traven says. “It certainly is revolutionizing the way we propagate.”

The evolution of lighting in horticulture has enabled growers to improve their operations in many ways, and the technological advances show no signs of stopping, especially with LEDs. As a researcher and supporter of the horticulture industry, Currey is looking forward to seeing the continued impact that lower fixture costs, updated technology and refined research have on growers’ operations and bottom lines, as well as to the quality of the plants, whether it’s more flavorful herbs, more compact plugs, or other benefits. “I’m most excited to see if LED lighting can add value to horticultural products to make our product more profitable and improve our industry,” he says.

Photo courtesy of Anthony van Hoven

Anthony van Hoven, president of Rapidan, Virginia grower Battlefield Farms, has been working in his family’s business for practically his entire life. As a child, he helped out in the greenhouse before attending Liberty University and returning to help run Battlefield alongside his father, Jerry.

Below, van Hoven explains why it’s important for Battlefield to be energy efficient, how he works to develop a healthy work culture and what he looks for at industry events.

Greenhouse Management: In December, [Battlefield Farms] obtained MPS-GAP certification. For a business of your size, why is getting that certification valuable? 

Anthony van Hoven: In 2010, we started with the MPS-ABC certification and worked our way up to the A+ ranking, which we have now. But we wanted to pursue it because it really helps you focus on the complete management of the things you do spend a lot of money on — the chemicals, the fertilizers, energy ... It’s a little bit of a different focus, but it’s the same principals. It helps me, with the team here, keep everyone focused on improving.

GM: Battlefield prides itself on having a strong organizational culture. What are the characteristics of that culture and how is it cultivated?

AvH: A hard-working, optimistic culture is what we want. Something that is very important to me is the general happiness of the employees and their attitude. With the right attitude, you can learn and do anything. And if you have that attitude and that kind of motivation inside, then the sky’s the limit for what you can attain and we try to cultivate that kind of attitude here. It’s not glass half-empty — it’s glass half-full and finding ways to improve what you’re doing. What I like to try and do is empower the managers, the supervisors, the line coordinators. They are doing something all day, every day and I’m not. If you have an idea of how you can make things better, I want to hear it. 

GM: When you go to an event like Cultivate, what are you looking to learn?

AvH: At an event like Cultivate, it’s not so much about what I’m trying to learn as far as new plants and new machinery or new chemicals or fertilizers. I stay very current with [that], so it’s not like I’m expecting to see something I haven’t seen. But at the same time, it’s a great chance, with the entire industry there, to talk to people face-to-face, go over any potential issues that there may be with certain suppliers. We’re planning for the next year, so it gives you a chance to talk to the people you work with instead of doing it on the phone or over email. You get a better feel for how the companies you work with are doing and what their challenges might be and how you can help.