So, you’ve decided to take the plunge and upgrade your grow room to LEDs. Simply unplug the HPS lights and install the LED lights. Better yields and lower electric bills – you are going to be a hero. Well, you might be a hero if you take into account how the switch to LEDs impacts your leaf surface temperature and the corresponding vapor pressure deficit (VPD).

It is well-established in plant biology that leaf surface temperature must be kept within a specific window to optimize primary metabolism (photosynthesis), as well as production of secondary metabolites. The relationship between leaf surface temperature and photosynthesis is shown in the figure below. The figure consists of data from a variety of plant species.

But leaf temperature is only part of the story. The critical factor is the interplay between leaf temperature and the relative humidity in the grow room. Those two factors (temperature and humidity) determine the vapor pressure deficit (VPD), which, in turn, determines transpiration efficacy and ultimately photosynthetic rates. An example of the relationship between temperature, humidity and VPD is illustrated in the chart below. To optimize production yield, the VPD must remain in the “sweet spot” identified in the green boxes.

High pressure sodium (HPS) lighting, has long been the workhorse in many indoor grow facilities. HPS emits in a broad portion of the electromagnetic spectrum that includes infrared (IR) energy – otherwise known as heat. IR energy from HPS heats the canopy and increases the leaf surface temperature. LED grow lights typically have only a small fraction of their emission in the IR portion of the spectrum, so they do not increase leaf surface temperature like HPS. In fact, it is typical to see a 5°-10° decrease in leaf surface temperature by changing the lighting from HPS to LED. If no other action is taken, the decrease in leaf temperature may throw the VPD out of its sweet spot – thereby decreasing transpiration and photosynthesis. This will most certainly not make you a hero in the grow room.  

So how do you ensure you are still in the proper VPD range after installing LED lights? Follow the steps below:

1. Understand your baseline. Measure the leaf surface temperature and relative humidity while you’re still using HPS. Although humidity is easily measured, measuring leaf surface temperature requires specialized equipment such as a forward-looking infrared camera. Here’s one IR camera that will do the job: tequipment.net/fliri7.html. Don’t assume the leaf surface temperature is the same as the ambient air; this is rarely the case. Once you’ve taken the measurements, the VPD can be determined.
2. Repeat step #1 after switching to LED.
3. Determine if your VPD is still in the optimal range. If it isn’t, you should:
   1. Increase the ambient air temperature to raise the leaf temperature to the target temperature that satisfies the VPD requirement.
   2. Modify the relative humidity in the room to bring the VPD into the ideal range. 

One reason LED grow lights are so efficient is that they don’t produce excess heat in the light beam like older technologies (including HPS). However, to fully achieve all the benefits of LED technology, growers must understand how the lower heat content will affect their plants and take the proper steps to achieve optimal production.

In 2009, the Department of Energy (DOE) created the LED Lighting Facts program to help manufacturers, utilities, and consumers in the early days of LED lighting, when products entered the market with little or no verified information on product performance. The voluntary DOE LED Lighting Facts effort paved the way for the mandatory Federal Trade Commission (FTC) label required for most commercial and residential lighting products (including incandescent, compact fluorescent, and LED light bulbs), which was introduced in 2010. This initiative had a significant impact in advancing the adoption of LED technology in general lighting.

Lighting Facts Label for Commercial & Residential Lighting

Today we are seeing a similar effort for grow lights.  Development of a lighting facts label for horticulture is being spearheaded by university researchers that believe there is a need for clarity and consistency in communicating to growers the performance metrics for horticultural lighting products. The objective is to create a label that is easy to read and understand and would aid in the comparison of products from different manufacturers. Researchers have proposed a horticulture lighting facts label that they hope will one day become an industry standard. Information reported on the label is intended to come from measurements taken at certified independent test labs.

Proposed Lighting Facts Label for Horticulture

Key information listed on the label:

• Light Output

Output within the photosynthetic active radiation (PAR) spectrum of 400-700nm is listed at the fixture’s nominal input power, which is also on the label.

• Spectral Power Distribution & Intensity

Many growers have a preference for the spectral composition of the light they need to optimize crop yield and health. The label provides a graph of the normalized photon flux vs. wavelength. It also quantitatively breaks down the light into its spectral components of red, green, blue, UV, far red and infrared. These spectral buckets are reported in units of intensity (umols/m²/sec) with the fixture mounted 2-feet (61cm) over the canopy.

• Uniformity

The proposed label displays a graph of the intensity of the light as a function of distance from the center of light (also at the 2-foot mounting height). This information provides insight into the uniformity of intensity on the canopy from a single fixture.

• Efficiency

Understanding how efficiently a grow light converts electrical input power to light output obviously has a major impact on the operating costs of a grow operation. The proposed label displays PAR efficiency in umols/joule.

• Color Quality

Although terms such as lumens and color rendering index (CRI) are not important to plants, they can be important to people working in a controlled growing environment. Of particular import, the proposed label lists the light fixture’s CRI, which indicates how accurately humans can see colors reflected from objects they are viewing. There are many grow lights on the market that consist primarily of blue and red LEDs, and it can be very difficult for people to determine plant health under those lights. The closer the CRI is to 100, the more accurately the plant’s colors (and health) can be determined by workers.

The proposed label is currently under review, and the team that created it is collecting feedback from industry stakeholders. Presently there is no requirement for approval of the label from the Department of Energy, so it is currently a voluntary standard. The hope is that once growers see the label on a few lighting products, they will demand its use from all lighting manufacturers. While benefits of the label to growers is clear, a major benefit to serious horticulture lighting manufacturers is as a weapon against low-quality products that overpromise, underdeliver and slow the adoption of new technologies.

LED lighting for controlled environment agriculture (CEA) continues to mature as new standards and regulations are implemented across the industry. And the emergence of the Design Lights Consortium (DLC) horticulture lighting program is an important step forward.

Design Lights Consortium is a non-profit organization with a mission of advancing the adoption of energy efficient lighting. The organization historically focused on general lighting applications such as retail lighting and street lighting. But very recently DLC started accepting submissions of LED grow lights for qualification testing and inclusion in its Horticulture Lighting Qualified Products List (QPL).

For growers, buying DLC listed products provides peace-of-mind that the lights meet rigorous performance, safety and reliability standards. Further, utilities are likely to begin mandating DLC listed lights in order to qualify for energy efficiency rebates.

A few of the critical performance and reliability requirements to achieve DLC listing include:

• Efficacy > 1.9 umol/J between 400-700nm
• Long-term performance: Q₉₀ > 36,000 hours photon flux maintenance
• Driver Lifetime: > 50,000 hours
• Warranty: > 5 years

A comprehensive overview of DLC horticulture lighting requirements is here: DLC Requirements

In addition to performance and reliability, DLC requires products to be certified by a relevant safety certification body in the United States or Canada. Underwriter’s Laboratories (UL), for example, has defined UL 8800 for the review and safety certification of horticulture lighting products.

Since the horticulture program is new for DLC, there are not currently any qualified lights on the horticulture QPL. However, Thrive Agritech is already in the process of having its LED grow light fixtures qualified by DLC, and anticipates having some of the first lights listed. To learn more about DLC, visit: www.designlights.org.

LED Lighting cut carbon dioxide emissions by 570 million tons in 2017

We all know that LEDs are efficient and can help save energy by displacing older, less efficient lighting technologies. But how much energy is really being saved? 162 coal-fired power plants worth of energy, according to IHS Markit.

The efficiency of LEDs is essentially what makes them environmentally friendly,” comments Jamie Fox, principal analyst, lighting & LEDs group. “Therefore, LED conversion is unlike other measures, which require people to reduce consumption or make lifestyle changes.”

We think Fox is 100% right. LED lighting has the opportunity to save massive amounts of energy, not because LEDs are efficient, but because they can be BETTER at providing light and happen to be efficient.

Growers select LED lighting because the technology has a better spectrum, can provide better uniformity and ultimately can help produce amazing plants with higher yield at a lower operational cost. The rest of the world benefits from reduced contribution to climate change and improved sustainability of our food and plant production industries.

Beyond this, not accounted for in the energy and CO2 savings estimates are the longer lifespan of LEDs. There are many pollutants created by producing, shipping and disposing of lighting products. By lasting 2-5x longer than conventional lighting, many of these pollutants are avoided. Even betters, LEDs don’t include heavy metals like mercury, making them more environmentally friendly at end-of-life.

We are proud to be part of an industry that is saving hundreds of millions of tons of CO2 from entering our atmosphere. We have a long way to go as a planet, but it is a great feeling to know that the path for our industry is Win-Win, saving energy and getting better light.

Weber Greenhouse installed supplemental LED lighting from Thrive Agritech to optimize basil production, especially in the low light periods of the year typical of upstate new york. The energy efficient full spectrum white lighting not only increases plant growth but also improves canopy consistency and plant morphology.

Increased basil sales result in a quick return on investment, especially considering the low operational costs of the Boost LED light bar. Installation was easy and economical, with each fixture connected end-to-end and mounted directly to the existing greenhouse truss system. Compared to other LED systems considered, ease of installation was a major benefit, especially considering each light row is operated and controlled with a single plug.

“Weber Greenhouse is a leader in advanced Controlled Environment Agriculture,” says Brian Bennett, CEO and Founder, Thrive Agritech. “We are thrilled to work with a company that represents the future of sustainable indoor plant production and support their efforts to achieve increased crop production while being environmentally sustainable.”

LED grow lighting has many advantages over high-pressure sodium, metal halide, and fluorescents – they use less energy, emit less heat, reduce water usage and have spectra that are optimized for plant growth.  Another great thing about LEDs is their reliability.  Instead of re-lamping every year, many LEDs have lifespans of 10 years or longer.  But as more growers transition to LED grow lighting, more questions and concerns arise.

For decades cannabis growers have been honing their grow “recipes” on their own and when the light technology “ingredient” changes so do the other variables like nutrient uptake, temperature, humidity requirements and so on.  Implementing LEDs into an already dialed in grow can be challenging so let’s look at the first step to make this a successful transition:

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