Advancing the quality of light

HOW DIFFERENT LED SPECTRA RENDER COLOURS IN THE BUILT ENVIRONMENT
Light-emitting diodes (LEDs) are capable of offering many more advantages than energy savings, meaning their value is well beyond providing more lumens per watt (LPW) than other light sources. Particularly, the spectral content of LEDs can be optimized to provide a rendered lighting quality preferred by humans, likely resulting in enhanced productivity and well-being.

LEDs started to gain mass appeal in commercial applications in the early 2000s. At that time, lighting companies optimized the spectral content for maximum efficacy (i.e. energy savings) to assure the technology was competitive with fluorescents. The strategy was to turn down the red content, thereby increase the green content, a spectrum the eye is most sensitive to. This resulted in an acceptable light quality still widely used today—LEDs with a colour rendering index (CRI) of 80 is common. They also constitute a baseline for most light sources specified in commercial environments.

LEDs with 90 CRI are also widely available from most luminaire manufacturers, and they constitute a higher quality light source rendering better colours. These LEDs are often found in specialty spaces, including healthcare facilities where colour rendition is paramount, especially in critical applications. The spectrum of 90 CRI LEDs has a higher red content than their 80 CRI counterparts, resulting in a light quality deemed to be more pleasant and natural, or more similar to natural light sources such as the sun.

Independent research conducted by Pacific Northwest National Laboratories (PNNL) and Penn State University (PSU) in the United States, as well as Zhejiang University in China, have converged to identify a spectrum preferred by humans. Technological advances in LEDs have now made it possible to render that light quality.

As the efficacy of LEDs reaches a plateau, a shift from maximizing energy efficiency to concentrating on how spaces are affecting human well-being is changing the design process of commercial environments. Many studies have shown that when humans are comfortable in an environment, they tend to be more productive, further supporting the idea buildings should have a greater focus on light quality. Global building certifications, such as WELL, are also contributing to an increased awareness of the importance of balancing human health and well-being with efficiency and sustainability.

Using this information, specifiers can finally switch the conversation to focus on the users of a space and select light sources that will not only be functional, sustainable, and esthetically pleasing, but also enhance the experience of occupants.

 

Quality of light initiatives

Some examples of quality of light initiatives actively being discussed in the industry include:

  • circadian lighting – aims at improving sleep and mood by providing the right light spectrum for the time of day;
  • warm dimming – replicates the quality of a halogen light source when an LED luminaire is dimmed down (this is commonly used in restaurants and other hospitality spaces where a warm and intimate ambiance is desirable, but often results in a warmer light and a colour temperature inconsistent across the range);
  • colour tuning – often associated with circadian lighting but is a separate subset as it can also be used for preference without trying to align with and stimulate the human circadian cycle;
  • spectral tuning – specialty lighting used in retail environments (e.g. the light spectrum of LEDs is tuned to create a specific effect, such as having the meat displayed in a meat locker appear as red and as fresh as possible, or for the clothing in a retail store to pop more); and
  • human preference – providing a light quality humans prefer overall and that will, as a result, make them feel more comfortable and at ease in an environment.

Several recent studies that have converging conclusions support the human preference initiative and define a spectrum preferred by humans regardless of gender, age, or cultural background.

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