What is circadian lighting?

Circadian lighting is lighting that supports our day/night cycles, broadly called circadian rhythms. In short, our bodies take cues from the light around us to wake up and go to sleep. Our bodies also use these cues to figure out when to activate various systems, processes, and cycles that are necessary for daily living.

How does circadian optimization improve quality of life?

Quality of light translates to quality of life. Have you felt exhausted and not known why, even if you've been eating and exercising well? Started gaining weight for reasons you don't understand? Wondered if your senses were dull, memory slow, reflexes out of step?

What if while you were driving your car to work on your regular commute, all the lights are flickering and stuck on yellow in all 4 directions at the intersection? For every intersection in the city? That's what it's like for a person's body to lack 490nm blue light signals; they still get to work, because no one would sit at the light forever, but there's delay, uncertainty, and dysfunction.

Circadian rhythms support the core of some of our bodies' most basic processes, and light is the key to those signaling mechanisms. Our eyes literally act as sensors for non-visual cues, and respond only to certain bands of light that normally come from waking up with the sun and seeking shelter with fire or darkness at night. Some of these processes include hormone regulation, ATP production, body temperature regulation, protein synthesis, digestion, and basic decision making. We're discovering more about these mechanisms every year, so this list is far from comprehensive.

For those who work off-hour or asynchronous shifts, circadian-optimized lighting can work for you, in an even more powerful way - it gives you back control of your day/night cycle, and makes those brutal 2nd or 3rd shifts more bearable, or at least as bearable as they would be if they happened during normal hours. Same for "clopening", when you have to close the shop then get right back up to do it again in the morning. App based lighting controls let you set your schedule according to your life while - slowly, gently, please - training your body. If you love this idea but aren't sure what the best way to recalibrate would be, send us an email and we'll help you figure it out.

Some studies are evaluating the degree to which out-of-phase circadian rhythms can become risk factors for major clinical depression, breast cancer, thyroid dysfunction, and heart attack - there's definitely a significant effect, we're just not sure how big an effect to call it. Here at Kirala Design, we suspect the answer is going to be an uncomfortable one.

With so many of us spending the vast majority of our time under electric light and minimal direct daylight, we've been starved of the light that supports our daily needs, and it's harming us in a very real way. (See bottom of blog for a small bibliography.) Those who get plenty of direct sunlight exposure at eye level - from being outside, right next to a window, or directly under a skylight - are probably already getting what they need.

Ultimately, we know the solution. And it boils down to including a spectrum of blue light at a wavelength of 490 nanometers (nm), with sufficient intensity and duration. After that, the main barriers are education and implementation.

What wavelengths of light spectra do we need?

490nm blue, 660nm red, and a mix of violets.

While practitioners and researchers are still learning about these processes, we've been studying them for years, and it's clear that we need a specific wavelength of blue light at 490 nanometers to signal our bodies to start the day. Incandescent sources typically contain 490nm, but to get what you need would cost too much energy and produce an uncomfortable amount of heat. The vast majority of LED and fluorescent light sources produced for the last 20 years have blue spectra in the 400-450nm range. However, being off by 10nm or even 5nm is enough to miss the light window that our bodies seek. 

It's worth mentioning that 490nm is not the only component that we need for well-supported circadian rhythms, and that everyone's body has different needs day-to-day. Near-infrared light in the 660-690nm range is also important, as are several wavelengths in the violet spectrum. Incidentally, 660nm is the wavelength that best penetrates human skin at high intensity, allowing us to see our veins; you can see this for yourself by turning your phone flashlight on and covering it with your little finger; kind of cool, right? See bibliography articles on the biological process for further reading.

How much of this 490nm blue light do we need?

Equivalent Melanopic Lux, or EML , is a vertical measurement taken at eye level of light brightness. Specifically, it measures light intensity in a given area.

Good: 150 EML

Better: 200 EML

Best: 275 EML

Simply put, if your lamps have these light levels and wavelengths, you reap the benefits.

The BIOS Skyview lamp, available in our shop, provides 200 EML all on its own when placed within 3ft of your eye at eye level. At 4ft, you're still getting 135 EML, so you'll definitely want to get some sun or supplement with other sources. Even so, what would really be best for most bodies is 275 EML, and for that we'll need to add more layers of light from other light sources, ideally from daylight or other circadian-optimized light. 

How long do we need to spend under this type of light?

Ideally, all our light would be optimized, and we wouldn't have to think about it.

Until then, as much as you can; sources vary, and we evolved to live under natural light from sunrise to sunset.

For breakpoints, what we've gathered is that...

...30 minutes during the start of your day is needed to trigger basic processes. Else, we tend to feel slow and operate like a laptop at low battery.

...3 hours seems to do the job while generally improving our mood, recovery, and outlook.

...12 hours looks like an advisable maximum; it keeps us alert during our waking hours, continually running and triggering important biological processes

...and 3-6 hours before sleep, we need to start eliminating all light - but especially blue light of all flavors - from our visual field.

There's a time and a place; all resource gathering must happen in moderation. The reason we would want to eliminate blue light before sleep is because biological processes need to eventually turn off, and pivot resources to other pathways which follow our night time rituals. A lot happens at night - we do so much more than just sleep, which is a mind-bendingly cool thing all on its own. We also rest our minds, recover from wear & tear or injury, make new neuron connections, grow our developing bodies, and process memories.

How did we miss something this big?

We - as an industry and global society - simply hadn't known any better yet. Our old light sources were deeply flawed, and the whole industry got so wildly excited when we discovered how to produce white light with LEDs that we forgot to really think about best practices. And we wouldn't have known how to address those issues at the time even if we had discovered them. The benefits of an immediate transition were so significant to life, health, and energy that rapid development felt necessary.

LED lights are better than old sources in almost every way: using 80% less energy than tungsten filament lamps, no toxic gases like kerosene, no deadly mercury like CFLs, dramatically reduced explosion risk compared to halogen, no start-up time like sodium, and produce a lot less heat than any of the others! They are also tiny, respond very well to different dimming systems, and can be produced very easily in large volume. For a time, they were more expensive and had bad color quality, but they're now equally priced over the lifetime of a product and have movie-grade color rendering.

The kicker is, producing LED white light requires a mix of powders called phosphors and rare earth materials, because white light is a prismatic mix of wavelengths and not a color itself. These materials act as filters changing the spectrum of light emitted from a source, and mixing them to appear as shades of white. From when you first started seeing LEDs in stores up until recently, the dominant blue component of white light was 450nm. While we thought this would be fine it turns out that 450nm blue light is not something out bodies respond to when it comes to circadian rhythms.

Only once we discovered and began to understand what are called intrinsically photosensitive retinal ganglion cells (ipRGCs) - which are non-visual light receptors in our eyes - did we learn what we'd been doing wrong for so long. Scientists found that these cells are triggered optimally by 490nm blue light, and that 450nm light just doesn't cut it. Even then, it took time for education and products to catch up. The discovery of this connection between ipRGCs, 490nm blue light, and circadian rhythms led to a Nobel Prize in 2017.

How do we know if the light and spectra are right?

Here's the punchline- a light source either emits useful 490nm light at a comfortable level, or it doesn't. There's no good industry standardized word to indicates this, yet - a waiting opportunity.

No combination of wavelengths gives the same effect as another wavelength when it comes to this - paint mixing metaphors serve poorly here. It's about triggering biosensors, not interpreting color.

Here are some examples of what certain kinds of lighting actually do:

HCL, or "Human centric lighting": While mildly accurate, we push back against this term at every opportunity. Humans are not the only lifeforms inhabiting the earth, and designing as if we are the only living creature that matter is a big part of how we got ourselves into a global climate crisis.

Tunable white lighting: Mixing doesn't count, so unless ALL of the sources have useful 490nm wavelengths, this type of lighting has no relevance to circadian optimization. Tunable white luminaires usually have the same cool/warm sources as the static white sources do, just paired together on the same platform.

Dynamic lighting: "Dynamic" simply means that the lighting can change. Contrasts to static lighting in that static is unchanging. How does it change? We don't know, this word tells us nothing more of use, and has no relevance to circadian related metrics.

Color changing lights: Again, mixing doesn't count, so unless the blue channel is fixed at 490nm, this type of lighting has no relevance to circadian optimization. Blue channels are usually 420-450nm.

RGBW lighting: Mixing still doesn't count, so unless the B or W have significant 490nm, this solution is unlikely to be effective. Royal Blue (for making pastel colors in RGB+RB sources) is typically 450nm.

We're working on models that are intuitively understandable to everyone at a glance. Until circadian optimized light sources replace the current standard, it's important to seek products that specifically mention 490nm as a product feature. 

Spectral Power Distribution (SPD) charts and LM-79 reports provide the hard data needed to tell if enough 490nm light is present for sure, but reading them takes some familiarity with lighting. You can request this product-specific data from manufacturers or anyone who responsibly sells lighting. 

And, yes, while there are products out there that make circadian claims but still miss the mark, most of them do a good job. Feel free to send us an email asking to review a product if you're not sure! We'd love to help improve the quality of light in everyone's lives, at no cost to you and no commitments required.

Want to dig deeper?

If you're someone who'd like to learn more about circadian rhythms, we invite you to contact us for a 1 hour AIA-accredited presentation on the subject, the science behind it, and some of the ways in which light affects our lives. Our Principal Designer, Haven Skyy, is NCQLP Lighting Certified (LC), a BIOS Certified Circadian Wellness Auditor (CWA), and approved BIOS reseller. Wherever your knowledge level is, we'll meet you there and grow together. He's taught chemistry and algebra to kindergartners, and leads the Navigating Lighting Design Decisions class multiple times per year.

Research into the effects of circadian rhythms is ongoing and thriving.

Here are some that we've found interesting. We'll add to this page over time as we find more cool content!

Study: Light Affects Mood and Learning through Distinct Retina-Brain Pathways
Directly links visual system components with mood, learning, and some of the mechanisms behind them.

Study: Human responses to bright light of different durations
A study published in The Journal of Physiology showed strong evidence for a non-linear resetting to the human circadian response to light duration.

Meta-review: Circadian rhythms in exercise performance, with implications for hormonal and muscular adaptation
A 28-study meta-review looked at the role of circadian rhythms in practicing soccer, cycling, swimming, resistance training, and racquet sports. Analysis showed enhanced fitness, strength, power, and coordination across all measured sports when circadian rhythms were properly entrained.

We're slowly working on summarizing the below articles for you. Here are their standard citations, for now:

LeGates TA, Fernandez DC, Hattar S. Light as a central modulator of circadian rhythms, sleep and affect. Nat Rev Neurosci. 2014;15(7):443-454. doi:10.1038/nrn3743

Ostrin LA, Abbott KS, Queener HM. Attenuation of short wavelengths alters sleep and the ipRGC pupil response. Ophthalmic Physiol Opt. 2017;37(4):440-450. doi:10.1111/opo.12385

Challet E, Kalsbeek A. Circadian Rhythms and Metabolism.; 2017. doi:10.3389/978-2-88945-282-8

Plano SA, Casiraghi LP, García Moro P, Paladino N, Golombek DA, Chiesa JJ. Circadian and Metabolic Effects of Light: Implications in Weight Homeostasis and Health. Front Neurol. 2017;8:558. doi:10.3389/fneur.2017.00558

Boyce P, Barriball E. Circadian rhythms and depression. Aust Fam Physician. 2010;39(5):307-310. doi:10.1136/bmj.2.5961.3

Buxton OM, L’Hermite-Balériaux M, Turek FW, van Cauter E. Daytime naps in darkness phase shift the human circadian rhythms of melatonin and thyrotropin secretion. Am J Physiol Regul Integr Comp Physiol. 2000;278(2):R373-R382. doi:10.1152/ajpregu.2000.278.2.R373

Kent ST, McClure LA, Crosson WL, Arnett DK, Wadley VG, Sathiakumar N. Effect of sunlight exposure on cognitive function among depressed and non-depressed participants: a REGARDS cross-sectional study. Environ Heal. 2009;8(1):34. doi:10.1186/1476-069X-8-34

Phipps-Nelson J, Redman JR, Dijk D-J, Rajaratnam SMW. Daytime exposure to bright light, as compared to dim light, decreases sleepiness and improves psychomotor vigilance performance. Sleep. 2003;26(6):695-700. http://www.ncbi.nlm.nih.gov/pubmed/14572122

Phillips AJK, Clerx WM, O’Brien CS, et al. Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing. Sci Rep. 2017;7(1):3216. doi:10.1038/s41598-017-03171-4

Koo YS, Song JY, Joo EY, et al. Outdoor artificial light at night, obesity, and sleep health: Cross-sectional analysis in the KoGES study. Chronobiol Int. 2016;33(3):301-314. doi:10.3109/07420528.2016.1143480

Beauchemin K, Hays P. Dying in the dark- sunshine, gender and outcomes in myocardial infarction. J R Soc Med. 1998;91:352-354