There’s been somewhat of a misconception developed over the years regarding circadian lighting (a.k.a. Human-Centric Lighting). It’s getting better than it used to be, but there’s still this idea among members of the smart home industry that all you need is controllable color temperature and light intensity, and you have a fully functional installation. If only. “True circadian lighting,” according to veteran lighting designer Alessio Urso, “Depends on so many external factors that are very difficult to control.”

Identifying What Influences Successful Circadian Entrainment

In our previous article talking about the subject, we mentioned the concept of circadian entrainment. For brevity’s sake, entrainment refers to the simulation of natural cues—in this case, lighting—to support our bodily clocks. The reason for that is that we used to spend 100% of our time outdoors, so all our sensory inputs came from the sun. Now, since we spend only 10% of our time outdoors, we can use circadian lighting to fill in that other 90%.

While manufacturers have made great strides in simplifying its implementation, however, there’s still a lot that a single light bulb can’t cover. In developing a proper installation, Urso points to a number of considerations that can influence entrainment in addition to lighting intensity and color temperature:

• Timing (when the transitions occur)
• Light history (how light presents itself in an individual’s context)
• Spatial distribution (how intense lighting distribution is and where it comes from)
• Spectrum (like color temperature, but more focused on non-visual wavelengths like ultraviolet)

Understanding the Nuances of Circadian-Effective Lighting

While some of these factors can be simple enough to implement, others may best be discussed with a lighting designer. Set timings to an automated schedule? Check. Make sure the lights have the proper CRI? Huh?

You can have five fixtures set to 5000K and they may all have a different effect on entrainment. This is due to their varying spectral output, better displayed by their color rendering index (CRI) score. CRIs above 95 come closer to natural daylight, which registers at 100. (Purists will defer to the newer TM-30-18 technical memorandum from the Illuminating Engineering Society for improved color-rendering assessments, particularly for LEDs.)

An effective scheme should also utilize both direct and indirect lighting, wall sconces, floor lamps, windows (i.e. shading control and photosensors) and more. This falls back to spatial distribution—or where the light is directed and how it disperses throughout the environment. Not only can it play a strong role in triggering circadian response, but it also provides tremendous visual comfort.

“Lighting coming from above the horizon is best in the morning,” Urso says, “but typical downlights are not effective because our brow bone blocks most of the light that needs to go into the eye.”

(Image from Journal of Biological Rhythms)

Anywhere from zero to 45 degrees above the horizon is the best spot for morning lighting. There, the light strikes photoreceptive cells in the retina that are responsible for the creation of melatonin, the body’s natural sleep aid.

It goes without saying, then, that effective evening scenes need the light to come from below the horizon, employing table lamps, step lights and other lower-level illumination wherever possible.

Can you remember the last building you stepped into, residential or otherwise, that employed these strategies?

At the End of the Artificial Day, It’s All About Teamwork

“For circadian lighting to be most effective, it has to be coordinated between the lighting designer, interior designer, architect, and controls specialist,” Urso says.

Integrators bring the technical expertise to help automate and control lighting, while designers bring the expertise behind the aesthetics and performance of the lighting itself. The architects find how these systems can fit into the physical building space, and the interior designer creates a comfortable, stylish and beautiful scene that plays to the transitions throughout the day.

With the amount of knowledge that goes into creating one of these systems, it’s hard to call circadian lighting, highly effective circadian lighting, a singular person’s job. So, if some of these professions are missing from your list of professional contacts and you’re interested in either learning more or perfecting your offering, it might be worthwhile to do a little outreach.