Human-centric lighting (HCL) and circadian lighting are two terms that often get thrown around interchangeably with one another. And at first blush, they do seem very similar. One uses color-tunable lighting to achieve better health outcomes and the other also uses color-tunable lighting to achieve better health outcomes.

But pan out a bit and things start to change. While human-centric lighting does describe an actual concept among lighting practitioners, the term got hijacked at one point for marketing purposes. If a bulb was capable of changing color or mimicking sunlight, it usually got the term human-centric lighting slapped onto it, and this is an assessment that others within the lighting industry, like David Warfel of Light Can Help You, seem to agree with for the most part.

I get why marketing scooped it up. Compared to ‘circadian lighting,’ the term ‘human-centric lighting’ is so much poppier and gets its point across without much explanation. Getting down to brass tacks, it’s also technically correct to call circadian lighting human-centric lighting. The problem is that not only does it make things unnecessarily confusing, it also drastically limits what is possible when it comes to HCL systems.

So, what is the difference between human centric lighting and circadian lighting? In this article, I’m going to go over what each term means, how they differ, and why its important for professionals to understand and explain the difference to their clients.

What is Circadian Lighting?

Circadian lighting is lighting that is used to directly impact our circadian rhythm. Our circadian rhythm is, put simply, the natural internal clock that governs our sleep/wake cycle. We’ve known about this for a while, but it wasn’t until roughly 2002 that we became aware of the exact systems that help govern this clock: namely, a photosensitive cell in the back of our eye that processes both visual and non-visual stimuli for the brain.

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We have an entire article going into the specifics of circadian lighting, how it is implemented today, and the research behind it. All you need to know here is that, because of this discovery, people suddenly realized how important light is when trying to regulate this clock. And ever since then, architects, designers, and researchers have been constantly working to better understand how our circadian rhythms are impacted by artificial light.

What is Human Centric Lighting?

Human-centric lighting, by comparison, is a much fresher concept. Still working on the discovery of the photopigment, human-centric lighting is, as described by lighting researcher Peter Boyce, “lighting devoted to enhancing human performance, comfort, health and wellbeing, individually or in some combination.”

Since the discovery of that photopigment back in 2002, researchers have begun to ascertain that it is responsible for far more than just regulating the circadian clock. As it turns out, the little photopigment is actually tapped in to some parts of the brain responsible for regulating mood. It also affects our endocrine system, adrenal system and our metabolic functions.

As a result of this greater understanding, researchers have come to realize that there is a lot that can be done with light that doesn’t have to tie into circadian cycles. Thus, human-centric lighting was coined to represent beneficial uses of light impacting both visual and non-visual experiences.

Circadian Lighting vs. Human Centric Lighting

You may already be asking yourself: “Wait, does that mean circadian lighting counts as human-centric lighting?” And the answer is yes. Because circadian lighting works to create a better health outcome using lighting, it falls under the umbrella of human-centric lighting. However, and this the part that people often get tripped up on, that does not mean HCL directly describes circadian lighting.

Think of it like squares and rectangles. All squares are rectangles, but not all rectangles are squares. All circadian lighting is human centric lighting, but not all human centric lighting is circadian lighting.

Circadian lighting is a single strategy among dozens, and not all those other strategies focus on recreating daylight effects. Not every single strategy has to focus on impacting the body’s circadian rhythm.

At its simplest, HCL strategies can focus on eliminating glare and flicker from lights, as these have been found to negatively affect occupant health. Growing more complex, human-centric lighting can also work to reverse the effects of seasonal affective disorder (SAD), lower stress levels, ease depression or be deployed to help increase cooperability and participation in schools.

Meanwhile, circadian lighting is exclusively tied to impacting the circadian cycle. When you think of automated color-tunable lighting that is focused on recreating the sun cycle for a better night’s sleep, that’s circadian lighting. It’s still good for you, but we shouldn’t limit ourselves thinking that’s all human-centric lighting is.

Why is it Important to Know the Difference?

Think of your role as an integrator. If a client views human-centric lighting as being nothing more than circadian lighting, they might never know how lighting can help them work better from home, have more energy during exercise or even help them de-stress after a long day.

I think at its core, human-centric lighting still follows a lot of circadian principles. At the end of the day, human-centric lighting may be focused more broadly on human experiences, but those experiences have a natural trigger, and if that trigger is sunlight, isn’t all human-centric lighting striving to simulate more natural lighting conditions?

There’s an old saying that “You don’t know what you don’t know.” After all this talking, it’s easy to write off circadian lighting vs. human-centric lighting as a matter of semantics. I won’t disagree with you on that one, it totally is. But it’s also, in a way, a matter of potential. It’s a missed opportunity to consider both concepts so simply.

Even if both strive to achieve more naturalistic lighting within a space, there’s a limit to circadian lighting, what it can do, and how it affects people. To perpetuate that misconception—that human-centric lighting and circadian lighting are one in the same—is to really hamstring what lighting can do.  

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