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  • Writer's pictureBrittany Lynch

Light and Health


Circadian Sun Cycles

Hello, my name is Brittany! I’m a lighting designer (not doctor, researcher, or scientist). And as a lighting designer, I find the topic of light and health fascinating.


The research linking the two has been ongoing for decades, but the real kickstart came when the WELL building standard adopted circadian lighting as a prerequisite and when the Circadian Stimulus (CS) metric became a UL design guideline. Now more than a buzzword, the lighting design community has metrics backed by research to apply to projects. Woohoo!


How Light Effects Our Circadian Rhythms (and Why It Is Important!)

But first, let me deliver a diluted summary of the research linking light and the human circadian rhythm so we are all on the same page. There are three known groups of photoreceptors in the eye. We have rods and cones, which form images. Then, we have non-image photoreceptors called intrinsically photoreceptive retinal ganglion cells (ipRGCs).


The ipRGCs convert neural signals received from the retina to the suprachiasmatic nuclei (SCN). The SCN is the part of the brain that controls our internal daily clock. In a nutshell, the ipRGCs tell the body if it is day or night. This is because these cells are most sensitive to blue light, which exists in abundance under the sunny sky.


Fast forward to the age of being indoors, research indicates that our ipRGCs aren’t receiving enough “signal” to make us properly entrained to the daily cycle. Side effects of this are feeling sluggish during the day when we should be awake (never mind your huge lunch and/or lack of daily physical activity). On the flip side, ipRGCs interpret blue light from screens as daytime, causing you feel awake at night (not because you are addicted to Netflix and/or social media past 9pm).


A diagram of the photoreceptors



But I’m a lighting designer! I can help! My whole job is to create luminous indoor environments. By using the power of science and research, I can manipulate light to help others entrain their circadian rhythm. I can do this by providing the right amount of spectrum, timing, duration, intensity, and distribution of light in the design of a space.


At first it seems simple.


  1. Choose a metric (there are at least 7).

  2. Design the layout.

  3. Complete the equation associated with the metric to determine the circadian response.


And voila! According to the research, you will not only be providing an impactful design, but people using the space will be more awake at work and will be able to get to bed on time at night!


A diagram of a person working at a desk with notes indicating Equivalent Melanopic Lux

There is always a "But..."

As I was happily involved with the light and health discussion, I started to pay attention to presentations put on by the IES, DOE, and other organizations involved in light and health research. Heck, I even did a presentation or two on how to calculate these metrics! But I soon became a victim of the Dunning Kruger effect. For those who don’t know about the Dunning Kruger effect it goes a little like this: the less you know, the more you think you know. The more you know, the more you realize you don’t know.


I realized that there is a lot I don’t know – I cannot determine if designing to a certain light and health metric will produce the correct phase shift/entrainment for each individual in a space.


For example, the equivalent melanopic lux (EML) metric, the one used in the WELL building standard, is based upon the intensity of light and spectrum measured at the eye. The metric identifies a range that should produce melatonin suppression, which should make one feel more awake. But this study is based on one person. What if the COVID vaccine trials were studied on one person? Would you expect to have the exact same experience as that one person? Of course not. Current research shows that some test subjects suppressed melatonin at much lower levels than the recommend EML range, and some needed more light above the recommended range.


Here’s another fun fact, just because your body suppresses melatonin production, doesn’t mean your body will shift its circadian rhythm. The research is still inconclusive. Yet several of the metrics, including EML and CS, assume that when the body suppresses melatonin production it shifts the circadian clock. So even if I could find that magic individual level of light at the eye that suppresses melatonin, it doesn’t automatically mean that the person would shift their clock and feel more awake during the day.



A graph illustrating the Dunning-Kruger Effect

Light and Health: The Only Guaranteed Solution

The practice of lighting design is not ready to administer a dose of blue light with guaranteed results. After diving further into the research, I am not convinced that applying one of the lighting metrics to a 9-5 environment will affect the human circadian cycle. As a caveat, health benefits of melatonin suppression are shown for shift workers and/or those involved in high stress environments.


I do look forward to more studies and peer reviewed research on the subject. Wouldn’t it be awesome if there was a reminder, similar to your fitbit, that told you it was time to suppress melatonin? Or, maybe each person gets a luminaire with an individually controlled spectrum, where you could tweak the blue light content. Those do exist.


For the time being, the vetted solution according to evolution is to GO OUTSIDE. Get outdoors, at least once a day, without sunglasses, and let your body do its thing. Let those ipRGCs soak up the blue light from the sun. Biology knows best. Instead of taking the time and expense to create a lighting design that cannot conclusively provide circadian entrainment, let’s save ourselves some time and money and get a little bit of sunlight.

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