Lighting for Circadian Rhythms – A Desirable Trend?

Our circadian rhythm is the built-in clock that regulates the timing of our biological processes and daily behavior, making us alert during the day and sleepy at night. A variety of environmental signals help to regulate it, the most prominent one being the cycle of light and dark - specifically the path of the sun. Lilian Fu, head of the buildings lighting practice in San Francisco, shares her thoughts on lighting for circadian rhythms.

Understanding Circadian Rhythms

There’s much discussion about how the use of electric lighting in buildings can support the body’s circadian system. The exposure to daylight, the quality and quantity of electric lighting, and task-appropriate illumination levels are thought to help improve energy, mood and productivity.

The concept has been around for a long time, but the research and applicability to our commercial industry are somewhat in their infancy. We don’t actually know everything about the way light stimulates our circadian system  to truly replicate all the natural processes that follow night and day, nor do we know whether that would actually be desirable in all cases. Yet, light fixture manufacturers have powered onward, some more carefully than others.

In the early 2000’s, it was discovered that certain cells in our eyes, called ipRGCs (Intrinsically Photosensitive Retinal Ganglion Cells), can stimulate our circadian process in the presence of light. One of these ipRGC’s has a maximum sensitivity at a particular wavelength – 490nm to be exact. A lot of manufacturers jumped on the bandwagon and started advertising lighting for health, or circadian lighting, all focused on this one particular discovery. But in the past year we’ve discovered that it’s only the tip of the iceberg. There are actually five of these ipRGCs, but there is research on only one of them so far. This is all very exciting for the lighting industry, and the medical community is also very interested. But we’re still all trying to better understand it.

The Impact of Lighting on Wellbeing

Where lighting does play a role on human comfort and behaviour is in the realm of Well buildings. We have worked on a number of projects that aim to meet the Well Building Standard (WBS), which defines metrics that the lighting needs to meet. When it comes to the light section, WBS provides guidelines for illumination ‘that are aimed to minimise disruption to the body’s circadian system, enhance productivity, support good sleep quality and provide appropriate visual acuity where needed’.

There are certainly things we can provide in lighting design that can help people feel comfortable and give them a sense of wellbeing.  For a lighting designer, these are common sense measures that we have always taken.  They include providing layers of lighting with illumination that is both direct and indirect, techniques for illuminating vertical surfaces in the environment and lighting for visual interest, which is also very important.

Coblentz Patch Duffy & Bass LLP © Joe Fletcher

Optimising Buildings with Lighting

Based in San Francisco as we are, we have a lot of tech company clients, who show great interest in creating work environments that maximise staff performance. They demonstrate how the workplace today is changing to be more focused on individuals and their performance, providing them with options to achieve the optimum working environment. Lighting is a key part of that.

Lighting is particularly important when it comes to facilities such as healthcare, where people spend most of their time indoors. For these buildings, we focus on providing maximum daylight as well as ensuring that there is good architectural lighting quality. 

Circadian Rhythm is Different for Everyone

The point about Circadian Rhythms is that we are all individuals, and the start and stop to the day is different for each person. There is increasing emphasis on user-controlled systems, where building occupants can select the type of lighting to suit their own personal circumstances. Currently we have a project for the Hayward Fire Training Centre, where we have proposed the idea of a dynamic tunable white lighting system for the firefighters’ sleeping quarters. Because they can be working all hours of the day and night, they would have the personal option of changing the quality of the light as they see fit. So at night, or when they are resting, they can have a warm light to help them feel relaxed; and during the day, or if they are on night shift, a brighter light would make them feel more awake.

What we must remember when it comes to creating good lighting quality in buildings is that every scheme must also take into account the economic and the architectural considerations as well as the human factor. It has to be a balance.


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