Indoor lighting and its effect on circadian rhythm

By Jille Kuipers

Perhaps you have sat in a meeting room with no windows for a prolonged period. How did it make you feel? For many of us we lose a sense of time, and feel tired and when we get outside the meeting room for a walk outside the building during a lunchbreak we just notice how dark it was inside or how bright it was outside.

Natural daylight offers non-visual benefits

Natural daylight helps us to see well, and feel well and also regulates our 24 hours cycle, which is known as the circadian rhythm. Daylight helps the body to understand what time of the day it is and guides us through the day from early morning to late afternoon and sunset. Whilst we often think that natural lighting is static, it is incredibly dynamic, changing in its intensity, direction, color, spectrum and much more.

 
Indoor lighting however often remains the same. It is primarily made to support the visual function of the human eye. Lighting products are very much focused on lumen output, which is the amount of light that the human eye perceives as bright and helps us to see. In higher-end spaces there is more attention to the quality of light, adding better color rendering fixtures, low glare options and more eye comfort considerations in lighting planning and design. 

 
When the first artificial light sources arrived they were incandescent, these light sources contain a majority of red in their light spectrum, this is compatible with the afternoon sun spectrum and does not stimulate the circadian rhythm. Sitting under incandescent lighting all day long would be equivalent to a whole day with sunset lighting and it would make our body yearn for more bright light around noon time. Fluorescent lighting promised energy savings and lots of visual light output. However, their lighting spectrum has spikes at different wavelengths and does not stimulate the circadian cycle. LEDs offered even more energy saving and their spectrum can be adjusted. However general LEDs have a lower circadian lighting component compared to natural daylight in the morning and noon time, and a much higher component in the late evening/ night. Hence you might have experienced the blue light from your phone that affects your sleep late at night. The current general lighting spectrums and the intensity of light deprive our body of signals like when it is time to slow down, get ready for sleep, or when to wake up, be more concentrated and alert.

Light is a timekeeper for the human body

The receptor in the human eye that regulars the circadian rhythm is most sensitive to light around 480nm which is in the blue range. The light that stimulates the circadian rhythm will make us feel awake, active and alert and stimulates the production of cortisol (also known as the stress hormone). it also suppresses the production of melatonin (also known as the sleep hormone) which makes us feel sleepy and relaxed. 
 
Exposure to unwanted blue light at the end of the day disrupts our circadian rhythm, it makes it harder to fall asleep even though we are tired and in need of rest. In the mornings the lower levels of blue light make it harder to feel energetic and productive at work. Poor sleep quality and suboptimal circadian cycle can affect our daily performance, for example, it can indirectly affect our ability to think, our mood, our appetite and so forth. In healthcare settings and care homes, it can affect the healing process as good sleep supports the recovery process. 

Making Circadian Lighting work for people

However, this problem can be fixed. There are several strategies to support the circadian rhythm in buildings such as workspaces. For example you may look at the office design, where are the workspaces and meeting rooms that people use most frequently? Where are people in the morning and noon time? how can you maximize the natural daylight in everyone's workspace? Access to daylight might also be beneficial in offering access to quality views. Quality views enhance the workplace and create synergies with circadian lighting as well as energy efficiency. Building standards such as LEED, WELL standard and others all have to some degree requirements around daylight, quality views and circadian rhythms. More daylight also enables possibilities to grow more plants indoor, for example green walls as an aesthetic feature in the office as well as enhancing biophilic design. Studies have shown that it can enhance the well-being of people in the space. 

Maximise daylight

An open-plan office might help to maximize the influx of natural daylight into the workspace. This has to be balanced with glare, noise and thermal design considerations. Looking at the building orientation and simulating daylight can help to determine where daylight can be harvested. 

Use human-centric lighting with wellbeing specifications

When selecting artificial lighting, consider LED lights that include human centric specifications and are energy efficient. A common misconception is that Correlated Color Temperature (CCT) includes the right corresponding circadian light. This is untrue. The CCT is primarily an indicator of what the color temperature is of white artificial light. i.e. how yellowish, white or blueish the light appears to the human eye. Tunable white refers to switching between these CCTs during the day. It will enhance the experience but does not impact the circadian cycle too much. However in general we can say that the warmer light (e.g. 2200K till 3000K) has a lower Melanopic lux content, and therefore stimulate the circadian rhythm less. This kind of light would be suitable in the afternoon and late evening. Whereas light with 5000 to 6500K would have a slightly higher Melanopic lux content and therefore stimulate the circadian rhythm more. Human centric lighting with wellbeing specifications will be able to show you data regarding circadian effective light and also help you to achieve a lighting design that can satisfy circadian requirements in building standards. 

The impact of light on your day

The daily cycle should be defined based on the full 24-hour cycle. Good lighting during the day will enable you to get better sleep at night. The brightest light should be around noon time so that the body can calibrate the internal body clock. Brighter light in the morning or earlier light in the morning makes one sleep earlier the next day and makes waking up easier and earlier. In other words, more light in the morning turns the sleep window counter clockwise. Evening light makes one sleep later and more difficult. It turns the sleep window clockwise.

What is Melanopic lux? 

Earlier we wrote about lumen and Melanopic lux. Lumen is the light output from a light source that is visible for the average human eye. Melanopic lux is a term that is recently becoming popular.

The function of light as a zeitgeber/timekeeper has long been assumed, however how light could influence the circadian rhythm was only revealed in the early 00’s when a third photoreceptor was discovered in the human eye that could regulate the circadian rhythm in people. In 2017 the Nobel prize in Physiology or Medicine was awarded to scientists that researched the circadian rhythm. With a better understanding of the scientific principle, it becomes easier to educate ourselves and develop better products to improve the well-being of people. It is important to note that Melanopic lux is about the amount of light that is received by the human eye. This means it is measured at the vertical plane (instead of horizontal, as you would do with e.g. lux on the floor or lux on a work desk). The height at which melanopic lux is measured is often 1.20m or 4” and the requirement is about 200 to 300 EML. The 1.20m or 4” is because that is the assumed average height of the eye when someone is sitting at their desk. In North America EML or CS is often used. The 200 to 300 EML is retrieved from different building standards. Some standards also specify the duration. For example between 7 am to 4 pm (UL design Guideline 24480). In Europe MEDI is more common.

What are guidelines for circadian lighting in the workplace? 

Here are some guidelines
Well V2 Q2 2022
At least 150 EML to 275 EML @ 1.2m for 4 hrs (latest start at noon)

UL Design Guideline 24480 (2020)
>0.3 CS at 100% view positions, @ 43” between 7 AM – 4 PM

Singapore Greenmark HW1 (2021)
There is no specific requirement mentioned on the intensity, only guidance on the respective CCT. We expect that they would include requirements in the future.
7 am to 10 am 3500-4000K 
10 am to 2 pm 5000K-6500K  
2 pm to 5 pm 3500K-4000K 
5 pm onwards 2700 -3000K

Hong Kong Code of Practice for Energy Efficiency of Building Services Installation (2021)
No requirement for Circadian lighting. We expect that they would include requirements in the future.
 
There are other guidelines such as from the Good Light Group. They include other options based on the age group. This is because senior people in general require more light as their eyes age.

Good Light Group

Daytime ≥ 500 MEDI
Evening ≤ 10 MEDI
Night time ≤ 1MEDI

Whilst the guidelines vary, there is a clear trend of indicating EML or another equivalent that correspondents with the light that has an impact on the circadian rhythm. There are some thresholds during the day and night. And it is important to measure the amount of light on the eye-height level. CCT can vary and is an optimization to make the experience better, however, it is more important to get the right EML first, as a prerequisite, before changing CCTs. It would be suboptimal to start adjusting CCT without getting to an adequate level of EML in the first place. 

Ask for help with circadian lighting

Daylight harvesting, Quality of light, Good lighting design continue to remain relevant. And lighting expands its role from a pure functional/ visual role, with an emotional role and now a biological role.

The three roles of light: Visual, Emotional, Biological. image: LuxBalance

If you’re looking to specify circadian lighting or lighting fixtures feel free to ask LuxBalance for advice. LuxBalance endorses the lighting solutions from CircadianLux. A range of professional lighting with wellbeing specifications. 
 
If you’re a distributor or retailer, contact LuxBalance for professional projects or wholesale options.
 
If you’re a consumer, please check out the CircadianLux Sleepy or Energy.