Why is lighting so complicated in controlled environment agriculture settings?

Light is the energetic powerhouse that drives photosynthetic activity in support of healthy plant growth. As such, the quantity (intensity), quality (color), and duration (exposure time) of light each play an important role in plant-growth activity and health. Light energy characteristics will either limit or enhance the rate and relative performance of plant development.


Light provides the sole source of energy for photosynthesis via plant pigment absorption, but the variances in its duration also serve as an external signal that triggers a transition to the next phase of plant growth, such as fruiting and flowering. The growth and development lifecycle for any given plant species is regulated by its unique requirements for light intensity, light duration (photoperiod), and light quality. While no single lighting technology offers optimal lighting characteristics for all plants or environmental conditions, controlled environment agriculture (CEA) facilities can realize significant benefits from lighting systems tailored to their specific applications and lighting needs.


Replicating Daylight


The faithful replication of the sun’s natural light is not a trivial task. In the 1930s a handful of very large lamps, rated at 75 to 100 kilowatts (kW) each, were developed by GE and Westinghouse in an attempt to replicate sunlight [Here is a fun article from the Smithsonian about Edison/Westinghouse Rivalry]. Despite their best efforts, to this day, there are no available man-made light sources capable of perfectly producing and sustaining sunlight’s energetic characteristics for identical plant photosynthetic activity. The closest approximation to a perfect solar-radiation profile is produced by a device known as a solar simulator.


Solar simulators typically resemble a large lighting luminaire (that is, an integrated lighting fixture), but the obvious similarities pretty much end there. Precisely manufactured and controlled, these hugely expensive devices are commonly used by solar industry researchers and manufacturers of solar photovoltaic (PV) cells and modules to test product performance under intensely controlled radiation and atmospheric conditions. Using a combination of light sources, including custom lamps and lasers, a better approximation of daylight can be produced. Despite its high level of technical sophistication, a solar simulator is still unable to entirely replicate sunlight’s temporal and spatial variations.


The Search for Standards


The measurement and reporting of light quantity, quality, and duration of availability provide indicators of healthy and productive plant development. Yet accurate light measurements are often overlooked, misunderstood, or insufficiently characterized for horticultural lighting applications. The continuous measurement of light energy availability, and to a lesser extent its quality, opens the door to the discovery of viable improvements toward optimal light delivery, a critical determinant of crop growth and health characteristics.


A wide and growing array of commercially available lighting equipment is now being designed, manufactured, and marketed directly for use in CEA applications. The reliable evaluation of performance for lighting-product performance is complicated by the diversity of technologies, the many variations in product design that “enhance” existing technology, and the wide variety of approaches to equipment and systems integration for commercial CEA applications. There are currently no established industry standards for the design, performance, integration, interoperability, and test requirements and conditions for horticultural lighting equipment. As a result, product specifications and performance details are often inconsistent from one manufacturer to the next, making the direct comparison of relative performance attributes like operational energy usage nearly impossible.


The serious need for equipment standardization— to enable more-reliable product evaluations and interoperability—is indicated by a large cloud of ambiguity hanging over the horticulture-lighting industry.







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