Can color-mixed technology improve lighting quality and energy efficiency?
By Michael Royer and Holly Ratafia
LEDs have transformed the architectural lighting market, yet there remains potential for improving energy efficiency and maximizing benefit to building occupants. Continued progress of color-mixed LED systems can contribute to both goals with anticipated benefits for luminous efficacy, application efficacy, human health, plant growth and general satisfaction. These benefits can be achieved because unlike static, broadband white light emitters that are ubiquitous today, color-mixed systems offer spectral flexibility. The prospect of widespread implementation of tunable lighting by the 2030s is exciting but will require overcoming several challenges and greater responsibility from the specifier. Now is the time to begin planning and developing effective strategies for deploying color-mixed systems. Here we examine the pros, cons and development path for this technology.
Not all color-mixed systems provide equal spectral flexibility. With only two variable components (typically called primaries), only a single path of chromaticity values lying between those two primaries can be realized. This is sometimes called white tuning. With three primaries, the chromaticity can be varied to anywhere within the triangular gamut (Figure 1) created by those three primaries (typically, a range of white and colored light), but there still may be limited ability to tune other spectral qualities. With four or more primaries, spectral quantities such as color rendition or melanopic:photopic ratio can be varied while holding chromaticity constant (i.e., creating metamers), allowing for greater flexibility in color appearance and spectral design for a variety of benefits.
THE POTENTIAL BENEFITS of color-mixed systems are noteworthy. Other than with two-primary products, tunable systems can produce a wide range of chromaticity values. This has the potential to facilitate better chromaticity consistency between different products, provided sufficient control capability and careful commissioning. Nevertheless, there may still be unintended mismatch arising from variations in the retinal response functions of individuals. In other words, lights with the same calculated chromaticity, but different spectral power distributions (SPDs), will likely not match in appearance for all observers. Tunable systems also have the potential to better maintain chromaticity over time, provided they employ some mechanism for predicting or detecting spectral changes and can apply the needed corrections. These features have the potential to simplify specification and extend the usable life of luminaires.
Many tunable systems are described as providing circadian-supportive lighting, but there is relatively little field research of this effect with tunable lighting. In particular, changing only CCT throughout the day may not have substantive physiological benefits and cannot provide the same degree of modulation for non-visual stimulation as changing intensity. Nonetheless, modulating the spectrum to vary melanopic content, chromaticity or both has no known disadvantages and may provide wellbeing benefits through physiological or psychological pathways.
Entertainment lighting has widely used mixtures of chromaticities of light. Tunable systems are the obvious choice for implementation of colored light in architectural spaces, with successful realization requiring not only careful selection of colors, but also consideration of contrast, adaptation, pattern and scale. Varying the spectral distribution can be used to set dynamic moods, provide dramatic accents, or offer seamless and responsive wayfinding cues. Some color-mixed systems allow for tailoring the\ appearance of the object(s) being illuminated. Besides this aesthetic benefit, other visual benefits could include enhanced visual performance and brightness perception.
BUT THERE ARE SOME CHALLENGES ahead. The potential benefits of color-mixed systems are dependent on improvements in color science, materials science and technology, as well as updates to codes and standards—for both measurement and specification. Advances in efficacy will come from new research into individual emitter materials, as well as from increasing knowledge of the quantity and type of primaries needed to achieve specific goals, which must be better quantified. The energy use improvements and cost reductions will be a key driver of increasing market share, regardless of tunability benefits.
Because color-mixed products produce a range of chromaticity and other qualities, characterizing their performance is quite complicated. New test methods, data presentation protocols and metrics will be needed to enable helpful product comparisons and specifications. The IES has work underway to provide helpful predictive advice. In the meantime, mock-ups are an invaluable, if time-intensive, tool.
TO MAXIMIZE THEIR POTENTIAL, most color-mixed lighting systems require more complex control systems and commissioning than conventional lighting systems, especially if multiple product types are installed in one space. Both the protocols used (e.g., DMX, DALI, proprietary) and the user interfaces may vary substantially. Like color-mixed systems, not all control systems provide equal performance. Deciding on a system requires the designer to weigh the benefits according to occupant needs, such as ease of use, flexibility and system complexity. Because effective design is dependent on equipment interoperability, specifiers should carefully test the performance and interoperability (if applicable) of lighting control systems.
Energy codes typically consider products based on maximum potential power draw, but tunable systems—designed for spectral flexibility rarely operate at maximum power and may constrain meeting lighting power density requirements. While achieving suitable code changes is a slow process, fortunately some product technology solutions for reducing power density are already available. For example, an alternative could be to limit the maximum power draw of the system to significantly less than the power draw of all primaries operating at maximum.
In summary, spectral flexibility may enhance both the emotional and physiological impact of architectural spaces, but it requires careful implementation and integration with interior surface selection, daylighting and building occupants. As increasing numbers of tunable systems are installed, demonstrations of exemplary systems and verification that they provide the intended benefits will be needed. Eventually, tunability is expected to become the bonus feature that comes with the most efficacious lighting products. In the meantime, carefully addressing current limitations will help ensure rapid development of this technology with commensurate benefits in quality and energy savings.