Circadian Correct Lighting: The Time is Now

The role lighting plays in supporting optimal human health and well-being

Posted in News on February 09, 2015

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There is a lot of information available on how to design lighting to optimize visual comfort, task performance and energy savings. What is less known is how to apply recent discoveries in the medical field about the role lighting plays in supporting optimal human health and well-being. This knowledge is based on research done a decade ago by scientists, including Dr. George Brainard from Thomas Jefferson University, which revealed that the human eye possesses a set of non-vision photoreceptors that helps regulate circadian rhythm and production of important neurochemicals, impacting everything from sleep and mood to the health of the human immune system.   


While researchers continue to develop a deeper understanding on the link between light and health, it is clear that architects and lighting designers need to consider properly timed exposure and avoidance of specific wavelengths of light. They also need to be more sensitive to the effect of differing light levels as a normal part of the lighting design process. Fortunately, even as research continues to reveal more nuances, it is not difficult to gain a foundational understanding of basic circadian lighting design principles. These principles are intuitive, and are patterned after the natural day/night cycle that humans evolved with until electric light sources started to be used less than 150 years ago: Expose normal populations to high levels of blue-rich light near 460 nanometers in the morning through early-afternoon, and eliminate these shorter wavelengths and reduce light levels in the late-afternoon. After 10:00 p.m. it is ideal to have total darkness - or if this is not practical - very low levels of warmer, red-rich light. Even an incandescent lamp can disrupt the circadian cycle if it is too bright.


Before circadian lighting was discovered, lay people and lighting professionals alike intuitively followed its general premises. Working in a brightly illuminated, cooler color temperature office during the day is associated with efficiency and productivity. Retreating to a dimmed, red-rich incandescent lighting environment at night – such as one found in a restaurant or home – is connected to feeling more relaxed and calm. And who doesn’t want an office window with a view and exposure to natural daylight? While IES standards and metrics that support circadian lighting may be years away, even without this specific data, lighting professionals already directionally and instinctively know what to do.


Considerations for Manufacturers

As more information on the connection between human health and lighting is discovered, there are several things that LED, luminaire and controls manufacturers can do to make it easier for lighting professionals to implement more effective circadian-correct lighting and promote widespread adoption. 


The first consideration is to commercialize solid state light engines which can be directed to contain the proper circadian action spectrum when used during the day, and to remove these shorter wavelengths at night. Just because a lamp is a cool 4100K, or even a cooler 6500K, does not mean it has the optimal amount of energy in the circadian-stimulating spectra. In fact, even lamps marketed as “full spectrum” generally do not have circadian-optimized spectra.   


A circadian-optimized light source can elicit the same response as a non-optimized source using as little as half the amount of light. This can help overcome objections of circadian lighting not being energy efficient, a concern that is magnified in facilities that house the elderly who require substantially more light to elicit a circadian response due to the clouding and yellowing that occurs to the lens of the human eye at an advanced age.


Figure 1 below, adopted from a chart published by the Lighting Research Center (1), compares the spectral content of full spectrum fluorescent and incandescent lamps to daylight. It is clear from the illustration that these artificial light sources contain far less circadian blue than daylight does.


Figure 1: Lighting Answers: Full-Spectrum Light Sources (adapted from Mark Rea et al.)


Because the spectra and amount of light needed to support optimal health and well-being changes depending on the time of day or night, tunable white luminaires that can be field-commissioned to dynamically change spectra and light levels throughout the day are critical to enable effective circadian lighting. The first tunable white luminaires in North America have just recently become commercially available and hold great promise for circadian lighting design, as is evidenced in the application pictured in figure 2.


The conference room pictured in figure 2 is equipped with tunable white LED luminaires that are controlled by pre-sets on a conventional 0-10 volt dimming system. This system allows occupants to select from several scenes including cool and bright shown at the far left, warm and bright shown in the middle, and warm and dim at the far right. This provides the flexibility to optimize lighting to support circadian health, as well as accommodate various room uses including audio/visual presentations, after hour social gatherings, and more.


Figure 2: Tunable white luminaires in a conference room application at Juno Lighting Group’s Des Plaines, Illinois, headquarters show the possibilities of circadian lighting.


While tunable white luminaires represent great progress, their spectra, as previously mentioned, need to be optimized to more effectively stimulate or prevent a circadian response. In addition, the industry needs to standardize on a tunable white controls protocol and develop control systems that are simple to commission and use. 


Manufacturers also need to re-evaluate the design and form factor of luminaires in the context of circadian lighting. To stimulate a circadian response, it is most effective to have a luminaire, or the placement of light from a luminaire, simulate the appearance of the sky. Larger, broader illuminated surfaces that can comfortably deliver higher levels of circadian-stimulating wavelengths to enter the non-vision photoreceptors, which nature appears to have cleverly concentrated in the lower back section of the eye to more efficiently collect blue rich light from above, are needed. This stands in contrast to the more common request of lighting designers for the manufacturer to minimize fixture  luminance as exemplified by low brightness downlight reflectors with deep source regression. 


Implementing Circadian Lighting


While circadian lighting is important in all types of residential and commercial facilities, the first applications will likely be interiors that support special populations including night shift workers and patients in long-term care facilities and hospitals. These special populations stand to benefit the most from proper circadian lighting due to their inability to access daylight when their bodies need it or avoid exposure to blue rich artificial light sources in the evening when it can be harmful. Operators of these facilities will also see benefits – they will reduce operating costs and be able to substantiate (and market) a better quality of life and care.


 As architects, lighting designers and organizations start to implement circadian lighting in their projects, they should consider the following:


  1. By simply understanding the basic circadian lighting design principles, there are solutions that can be put into place today. I had the opportunity to speak about human centric lighting in 2014 at LIGHTFAIR International on a panel that included Joan Roberts, a photo biologist from Fordham University and Kimberly Mercier, a principal at Lighting Design Innovations. In her segment, Kim referenced a project that she and Joan collaborated on where a forty-cent piece of red theatrical gel was placed over fluorescent lamps to create night time lighting in hallways of a nursing home. Without any “new” technology or sophisticated controls, this simple design decision dramatically improved residents’ sleep patterns, daytime alertness and social engagement. Simple techniques like using a theatrical gel, specifying warm dimming or tunable white LED products where they already exist, or installing two circuits of warm and cool light sources that can be mixed are all options. It is also helpful to understand that the sub-optimized circadian spectra in available light sources can be compensated for by designs that allow higher illuminance to reach the eye than might ordinarily be required for just vision. While these solutions may not be optimal, they still can contribute toward creating environments that support circadian health.
  2. When speaking with luminaire, control and LED manufacturers, let them know that circadian lighting is important. Manufacturers need to hear more from the lighting design community that we should prioritize circadian lighting fixtures on our product development roadmaps, which are being pulled in many directions. It was interesting to note that at the 2012 Light + Building show in Germany that many European manufacturers were actively promoting tunable white circadian lighting solutions, yet at the 2014 show, references to human centric lighting in manufacturer’s booths were scarce. One of the reasons manufacturers have not developed more circadian lighting solutions may be because there are not enough project requests to drive development.

  3. There are many resources available online about circadian lighting, including from the Lighting Research Center. If you cannot find products or data to support your circadian lighting projects, know that there are manufacturers that are capable and willing to collaborate to provide information and develop solutions. These early collaborations will be important to move the entire industry forward by providing a base of applications to evaluate and share the results.



While still a new concept, circadian lighting is already finding its way into lighting design using existing LED, luminaire and control technologies. As manufacturers continue to develop improved circadian lighting solutions and the industry works towards adopting circadian lighting metrics, it will certainly become easier to implement more effective designs. Dr. Mark Rea, director of the Lighting Research Institute, offered encouragement during a recent conversation, saying there is already enough information available about the amount of circadian light and doses for various age groups to establish effective standards.


As someone on the manufacturing side of lighting, I encourage specifiers to give us the confidence that if we prioritize circadian lighting product development, meaningful specifications will follow. If we sustain a dialogue and collaborate, I am confident that circadian lighting solutions will become more commonplace over the next few years.   



  1. Adapted from Mark Rea et al. (2003) Lighting Answers: Full-Spectrum Light Sources. Troy, NY: Lighting Research Center, Rensselaer Polytechnic Institute.


About the Author: Scott Roos, vice president product design, Juno Lighting Group by Schneider Electric Scott Roos has 35 years of experience in the lighting industry encompassing product design, marketing, product management and lighting education. During the course of his career, he has worked on products that have earned numerous patents and awards including the Industrial Design Excellence Award and the LIGHTFAIR Technical Innovation Product award. Most recently Scott has been focusing on human centric lighting and spoke on the topic at LightFair 2014 in the seminar Human Centric Lighting:  From Theory to Practice.  Scott has a BFA in Industrial Design from the University of Illinois and an MBA from De Paul University.