Shedding Light on the Debate Between Dynamic Spectrum and Fixed White LEDs
The debate between dynamic spectrum and fixed white LEDs is intensifying. Professor James Eaves, in his February 24 Greenhouse Grower article "What Are the Trade-offs of Dynamic Spectrum LEDs in Horticulture," dissects the intricacies of this lighting innovation. As growers assess their options, numerous factors come into play. Let's take a moment to delve into who stands to gain the most from embracing dynamic LEDs, shedding light on the practical implications for commercial growers, research facilities, and specialized crop cultivators.
When growers opt for fixed-spectrum white LEDs, they're choosing a lighting solution that utilizes phosphors to generate white light. However, this method comes with inherent inefficiencies as phosphors waste energy in three ways. Firstly, they convert high-energy blue light into lower-energy wavelengths like green, yellow, orange, and red, leading to energy loss and reducing overall efficiency. Additionally, the converted light is emitted in all directions, including back toward the LED chips, resulting in some light being absorbed rather than efficiently reflected or re-emitted, further decreasing efficiency. Moreover, both blue light and down-converted light are scattered in various directions by the phosphor particles, causing reabsorption and additional energy loss, contributing to further inefficiencies in the lighting system.
Despite these inefficiencies, Eaves touts the benefits of phosphor-containing LEDs, such as their high Color Rendering Index (CRI) which improves visibility for human inspection and creates a comfortable work environment. Moreover, their fixed spectrum operation simplifies usage, requiring only dimming controls for brightness and Photosynthetic Photon Flux Density (PPFD) management, making them suitable for growers seeking ease of use. Eaves raises concerns about dynamic spectrum LEDs, noting their higher initial costs and potential ongoing software fees, as well as potential increased maintenance due to additional electronics.
While it's true that spectrum-tunable LEDs may have a higher initial cost and require more expertise to utilize effectively, dismissing them outright overlooks their potential long-term benefits. Yes, for growers with short-term horizons or limited resources, fixed-spectrum LEDs may suffice. However, for those aiming to maximize quality, productivity, and market competitiveness over the long term, spectrum-tunable lighting offers distinct advantages.
The ability to tailor light spectra to specific crops, growth stages, or environmental conditions can significantly enhance yield, quality, and resource efficiency. Furthermore, while spectrum-tunable systems may require a learning curve initially, the potential return on investment through optimized growth outcomes and resource savings can outweigh the initial challenges.
Growers equipped to leverage tunable lighting typically possess a commitment to research and development alongside a nuanced understanding of plant growth and lighting dynamics. These growers prioritize continual improvement strategies, utilizing trial rooms and experimentation to optimize growth conditions. Moreover, growers seeking to dominate their niche markets over the long term find value in spectrum-tunable LEDs, viewing them as essential tools for achieving superior crop quality and yield. These growers understand the nuanced relationship between light spectra and plant development, leveraging tunable lighting to unlock precise control over growth parameters and drive sustainable competitive advantage in their operations.
Following the advent of the adult-use market in California, a Sonoma County cannabis grower trialed narrow-band spectrum-tunable LED fixtures. Compared to HID lamps, these LEDs yielded remarkable blooming-phase results, boasting a 56% increase in yield per watt, 41.5% higher THC concentration, and 57% more terpenes. Encouraged by these findings, they transitioned to LEDs across their facilities, observing consistent improvements. Furthermore, utilizing different LED spectra in the vegging phase enhanced the rooting, stem thickness, and internodal spacing, surpassing outcomes achieved with previous lamps. This trial unequivocally demonstrated the superior performance of spectrum-tunable LEDs in comparison to other LED options.
Continual improvement and R&D practices extend beyond cannabis growers; they are embraced by all sectors seeking precision expression of crop characteristics. For instance, growers focusing on traits like sweetness and flavor in strawberries leverage precision in all facets of cultivation, including lighting strategies. As the controlled environment agriculture (CEA) industry progresses, opportunities for optimizing fruiting and flowering plants will expand further. With ongoing advancements in technology and understanding, growers across different crop sectors are poised to benefit from tailored lighting solutions that enhance crop quality and yield, reflecting a broader trend toward precision-driven agriculture.
For growers committed to long-term investment, tunable-spectrum narrowband LED lighting presents significant economic advantages. With a yield-efficiency advantage exceeding ten percent over other LED types and lower electricity costs, the savings over a five-year period can surpass three times the capital cost difference between high-quality lighting systems and run-of-the-mill lighting systems. Notably, these LED luminaires boast higher reliability and require less electronics compared to other options, enhancing operational efficiency, and reducing maintenance concerns. Moreover, the best operate at safer low-voltage DC, minimizing risks associated with high-voltage AC lines. Ultimately, for growers prioritizing sustainability, performance, and cost-effectiveness, tunable narrowband LEDs emerge as a compelling choice.
A tunable narrowband far-red spectral component offers three additional advantages. Firstly, these low-energy photons, combined with deep red photons, activate a low-energy metabolic pathway in what is known as the Emerson effect. This can lead to enhanced yields for certain cultivars grown under saturation light levels. Secondly, the ratio of far-red to red light significantly influences plants' shade-avoidance response. Adjusting this ratio allows growers to optimize plant growth, preventing excessive elongation or stunted development. Thirdly, tuning to a far-red-dominant spectrum at the end of each photoperiod accelerates the conversion of Pfr phytochrome to the Pr state. Normally, this conversion takes up to 90 minutes in dark conditions, but with tunable lighting, it can be achieved within minutes. This capability enables growers to induce sleep mode in plants faster, allowing for extended photoperiods without affecting blooming in short-day plants.
The best of narrowband tunable LED luminaires offer higher reliability and simpler electronics compared to other luminaires on the market. Unlike most luminaires, which operate at high AC voltages (220 to 480 VAC) and require various safety features such as surge protection and voltage regulation, tunable narrowband light bars operating on low-voltage DC have streamlined circuitry. They contain only current-limiting circuitry and no electrolytic capacitors, reducing the risk of component failure, especially at elevated operating temperatures. The power electronics are housed in remote power supplies similar to those used in server farms, ensuring cool operation, reliability, and easy replaceability. Moreover, the voltage provided to the luminaires is a safe low-voltage DC, minimizing safety concerns associated with high AC voltages.
In the ongoing debate between dynamic spectrum and fixed white LEDs, growers face critical decisions in their pursuit of the best lighting solutions. While fixed-spectrum LEDs provide simplicity, dynamic spectrum lighting offers the potential for customized crop management and sustainable efficiency improvements over time. The economic and technical advantages of spectrum-tunable LED luminaires make them an appealing option for growers aiming for sustainable, high-performance lighting solutions tailored to their unique requirements and goals.
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