Guest post by Steve Mesh, LC
Because of recent trends in the lighting industry, it is now possible to “dial in” a desired color temperature in certain light fixtures at specific times of the day or night. One of the main trends making this possible is the mixture of different color LEDs in architectural fixtures. For example, a fixture may contain predominantly cool colored LEDs (e.g., 4000K). If the LED array is supplemented by red LEDs, then the color output of the fixture can be changed from “cool white” to “warm white” as long as the different color LEDs can be separately controlled. If a fixture contains an RGB LED matrix, then a much greater gamut (range) of color output can be achieved.
The second trend facilitating this ability to tune different colors is the availability of much more sophisticated control systems for architectural lighting. Achieving different colors of light used to be in the exclusive purview of the theatrical world. Digitization and individual fixture addressability are emblematic of the recent paradigm shift in architectural control systems. More and more systems now contain standard options allowing the user to manually change or even preset the color temperature of individual fixtures based on time of day, not just the light output.
The Lighting Research Center has recently proposed a new metric regarding circadian stimulus (“Designing with Circadian Stimulus”, LD+A, October 2016). Two of the main factors that affect the proposed metrics are 1) light level, and 2) spectral output of the light source. In the LD+A article, the authors explain that there are two major benefits to being able to tune the coloration – as well as the output – of specific fixtures. One is to provide appropriate “dosage” based on a fixture’s specific “CS” value (at a given light output and coloration) at any point during the day. Another benefit is that the output and coloration can be substantially changed to serve as an “alert.” That might entail at least a temporary radical shift in output or coloration to serve as a “message”, regardless of the impact on appropriate dosing for the body’s circadian rhythm.
Where might “tunable white” lighting be useful? A perfect application example is a submarine. While submerged, there may be no reference to daylight for weeks or months at a time. Varying the light levels and cycling the coloration from warm to cool to warm can emulate natural daylight to help regulate the biological clocks of the submariners.
Even when daylight is present (as it is in most spaces), varying light levels and color output can similarly mimic natural conditions. Some studies suggest that this has a positive affect on attentiveness and productivity. As such, office workers may benefit from the impact of tunable white lighting. Another application that may benefit is the classroom. In addition to the prospective benefit of increased attentiveness, studies have shown that the sleep cycles of school-aged children (especially teenagers) may be better regulated by the use of lighting that mimics and reinforces natural daylighting cycles of intensity and coloration (if necessary, we can probably find a reference to an LRC study about this). In order to achieve these benefits, it is essential to use fixtures that allow you to modify the output and coloration. Obviously, you must also deploy a control system that allows for setting (or preferably pre-setting) different light levels and color temperatures. Various manufacturers have recently introduced such fixtures and control systems. As the $6 Million Man once said, “We have the technology.”
Tunable white lighting systems may also be used for specific effect as opposed to helping to regulate the body’s circadian clock. For example, in a classroom, factory or office, a change in light level and coloration right before lunch can signal that it’s time to stop working (or learning) and get ready to leave. Upon returning from lunch, a substantially different light level and coloration may help to keep occupants “alert” (similar to the effect of having a cup of caffeinated coffee). Toward the end of the day, a change to lower light levels and warmer color temperatures can help to signal that the workday or school day is coming to a close.
Another application that might benefit from tunable white lighting is a retail space. Varying the light output and coloration during the day may help to stimulate sales by adding variety into the ambiance of the space. It might also be used as an “alert” function. For example, some change in light level and coloration might precede an announcement about specific sale items.
Restaurants and other hospitality spaces can also use tunable white lighting to change the ambiance based on the time of day. For example, a restaurant may dial in higher light levels and cooler colors of light for breakfast and lunch, but select lower levels of light and warmer coloration that may be more appropriate for dinner time.
Any change to light coloration (and light level) will have an impact on the physiological effects on the human body. Just remember that it will also have an effect on the visual environment – meaning the appearance of objects, finishes and people. If you have any questions about the impact of tunable white lighting, it may be a good idea to consult a lighting professional.