What is circadian lighting? What is human-centric lighting? And when should we be using these different types of lighting?

First, let’s establish a baseline that we can call “normal lighting.” We’ve taken light, stripped its beauty, magic, and health benefits, and then pushed the freeze button to make sure it never changed. This is our current normal.  

Circadian lighting is not normal. I am going to define it as lighting that is fully synchronized with daylight. When the sun rises, circadian lighting turns on at a bright warm glow. When the sun hits the middle of the sky at noon, circadian lighting is at its brightest and bluest. As the sun moves lower on the horizon, circadian lighting begins to dim and warm towards sunset. And when the sun sets, and the sky is dark, circadian lighting is turned off and completely dark.  

In other words, circadian lighting is natural lighting, electrified and brought indoors, fully synchronized with what is happening outside. For a few years, I thought this was the ideal solution to lighting problems. Then I saw the results and was deeply unsatisfied but could not immediately put my finger on why I disliked circadian lighting so much. 

I know now why I disliked those early adoptions of circadian lighting, and the answer is somewhat complicated and at the same time simple: synchronization with daylight does not work well for our societal needs, and unified color temperatures are like living in a sepia-toned photograph from the late 1800s.  

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The Case for Using Human-Centric Lighting Over Circadian Lighting

Enter human-centric lighting (HCL). To me, HCL is a careful balance of our bodies’ biological need for natural light and our societal demands for increased productivity and extended play. HCL mimics, without strict adherence, the rise and fall of the sun and the passing of seasons, while giving us enough light to do what we need to do even after sunset. And it recognizes our desire — perhaps our need — for dynamic variety. 

If circadian lighting brightens when the sun rises, HCL brightens when we rise, effectively making sunrise happen on our schedule instead of the universe’s. Personally, I would love to wake with the sun and go to sleep with natural darkness, but there are good portions of the year where that would make for very short days and very long nights.  

If I lived with a circadian lighting system in a Wisconsin winter, I would wake up around 8 a.m., show up for work about 10 a.m. and clock out around 2 p.m. so I could eat dinner, finish my chores, and go back to bed around 5. My schedule would be a little bit different every day, depending on weather and the continual change of natural light, and that might make it hard to schedule meetings. Given that I am, in this scenario, working a four-hour day minus a lunch break, that’s going to make it tough to meet goals and deadlines. 

I would rather have HCL system that begins to glow around 5 a.m., gently wakes me without an alarm around 5:30, energizes me from 8 a.m. until 5 p.m., and then gradually dims to prepare me for sleep around 9.  

We need light to see what we are doing, and that can mean anything from shaving at 6:30 a.m. to reading a book at 9 p.m. Circadian lighting doesn’t care what light we need to for task, it simply cares about what the sun is (or is not) doing. This does not work very well for human lifestyles.  

Circadian lighting, at least the variety that carefully matches all color temperatures in a space and synchronizes them with sunlight, looks ugly to me. Unified color temperatures look bad because they are decidedly unnatural. Yes, our quest for “natural light” has taken us further from it by stripping out the dynamic variety present in real life.  

David Warfel is Chief Evangelist of Light at design firm Light Can Help You (lightcanhelpyou.com)

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