The Design Light Consortium (DLC) has devised some performance guidelines for horticultural and agricultural lighting. These guidelines set an efficiency baseline at the level of 12 percent more efficient than second most efficient type of grow lights on the market, high-pressure sodium. So, any grow lights that meet their standard of efficiency in terms of PPE (photosynthetic photon efficacy), expressed in μmol/J, must at least 12 percent more efficient than high-pressure sodium lights.
I spoke with Damon Bosetti, DLC’s technical manager about these guidelines. Damon headed up the horticultural lighting work of creating a consensus among industry experts for the standards.
“We’re depending on the research and standards communities to come up with plant- and facility-specific best practices for lighting applications. In the general lighting world, IES has Recommended Practices for tunnels, runways, offices, you name it. That’s what we need here!” Damon said.
DLC Interviewed 20 Different Grow Light Fixture Makers
According to Damon, DLC conducted interviews with 20 different grow light fixture makers including major brands and many small independent grow light makers that only make grow lights. They also consulted the American Society of Agricultural and Biological Engineers (ASABE), and Greenhouse Lighting and System Engineering (GLASE) at Cornell University.
He pointed out that the standards are all product specific and performance specific for general grow light applications.
Damon gave the analogy of someone attempting to build a house. “Where DLC comes in is in ensuring that there’s a trusted, third-party-verified database of certified product performance data to use when coming up with designs that meet these best practices. Someone building a house will go much more slowly if they need to measure and strength-test every single piece of lumber – that’s why we have a standard for defining the size and strength of 2x4s, 2x10s, etc. With standardized product data, assembling them into a high-functioning whole goes much more easily, “ Damon said.
He noted that the guidelines are meant for all types of LED grow lights These include the kind with just white light and those with multiple colors. Damon also sid that while the DLC wanted to include UV light as part of the standard, the only way to measure UV light accurately is to use extremely expensive equipment. UV light has so much energy, according to Damon, that much of it is absorbed in standard light measurement spheres. So, the standard does not prohibit the use of UV light, it simply does not refer to it until the test procedure can become more widely available (affordable) and standardized.
Since the DLC considers the total power usage of the fixture, the use of UV (or any emission that does not add to photosynthetic photon flux) does reduce the overall efficiency of the grow lights as measured by the test standards.
Experimentation Still Needed
On the other hand, much has yet to be learned through experimentation. The use of grow lights close up versus far away is an area that needs research to define what works and what doesn’t for particular plants.
IES guidelines for general lighting and measurements based on these guidelines such as light output require the light to be at least five times the maximum dimension of the source. So, at the very close ranges that verticle farms are beginning to use, accurate emission data (in both angle and spectrum) is much less known. Damon says that the IES is attempting to devise a measurement standard for closer emission.
So, while gardeners and growers do not have to start from zero in setting up their grow lights, they will still have much to learn about what works best for their particular plants, and what distance to position their lights from.
“We are depending on the research to come up with the floor plan x for growing plant y, “ he said.
In the future, Damon says that the DLC intends to further refine the distinction among grow lights of sole source versus those for greenhouses, and also those that are analogous to high bay lights, and perhaps other applications that emerge.