The Secrets of Lighting Design and Circadian Rhythm

During a 24-hour day, exposure to light and darkness in your environment plays a major role in regulating your sleep/wake cycles, body temperature, blood pressure, hormone release – essentially all the moving cogs and pieces of your body clock. In a world of electric light, television, smart phones and built environments, here’s a guide for understanding your circadian rhythm while optimizing your lighting to better emulate the natural environment.

Light & Circadian Rhythm

At the core of circadian rhythm is your relationship with light, which acts as the maestro of many meticulously orchestrated biological processes. To better align your circadian rhythm, understanding lighting design specific to each system is critical.

But before we get into the specifics of electric light and applications in the built environment (below), let’s unpack some key facts about human circadian rhythm in the provided infographic. Incredibly complex and extensively studied, this is just the tip of the iceberg – but it does serve as a primer for understanding the basics of this critical field of study for builders, lighting experts, architects, and designers to name a few.

In Review: The Basics of Circadian Rhythm

To better align your circadian rhythm to natural 24-hour cycles caused by the rotation of the earth, it all starts with knowing the key components – including light itself, melanopsin, the suprachiasmatic nucleus, and melatonin.

The Maestro

At the core of circadian rhythm is light, which acts as the maestro of many meticulously orchestrated biological processes. The pineal gland is stopped from producing melatonin when light-induced activation of the SCN occurs, creating alertness.

The Messenger

A photopigment receptor protein found in retinal ganglion cells in the eye, melanopsin acts as a messenger, sending signals to the suprachiasmatic nucleus when exposed to light.

The Pacemaker

Explained in greater detail below, the suprachiasmatic nucleus (SCN) of the hypothalamus houses the circadian pacemaker, which receives light/dark signals from the eye’s retinal ganglion cells.

The Sandman

Darkness promotes production of melatonin in the pineal gland, causing sleepiness. While melatonin plays many roles, its secretion (or lack thereof) is critical to sleep-wake cycles.
Human-Centric Lighting

For lighting professionals, this term is not new – but it’s changing each year. Human-Centric Lighting (HCL) draws a line between light and wellbeing with a foot planted firmly in verified science. Beyond the health benefits that HCL could yield, it has opened up market opportunities for designers, lighting companies, and of course, consumers. Adding light color temperature to the mix, many smart technologies are becoming more integrated in homes to adjust light intensity and temperature to better suite natural cycles at appropriate times of day.

Biologically Effective Lighting

At its core, biologically effective lighting helps to improve cognitive performance. As LEDs Magazine points out, a link has even been found between high-CCT lighting and enhanced alertness. A 2015 article points to several studies with eye-opening insights that are hard to ignore:

A 200 person office implemented HCL luminaries. While annual electric costs rose from approximately $7,790 to $10,000, productivity rose 1.15%, which is equivalent to two additional output hours each month. A 1% decrease in sick days was also reported.

When HCL was installed, a school with 1,000 students and 80 teachers increased annual energy costs from approximately $8,900 to $12,240. However, a 15% improvement in cognitive performance was noted in some students while 5.3% of students suffering from ADHD benefited from a 10% reduction in education and healthcare costs.

Emotionally Effective Lighting

Published in Proceeding of the National Academy of Sciences of the United States of America (PNAS), “Spectral quality of light modulates emotional brain responses in humans” touches on the value of emotionally effective lighting in view of seasonal affective disorder:

Light therapy is the treatment of choice for seasonal affective disorder (SAD) and is a promising treatment for other major affective disorders, suggesting that light can modulate mood in the long term.– PNAS

Tying back to key components of circadian rhythm, “a polymorphism in the melanopsin gene has recently been associated with SAD,” according to the report. Blue-enriched light is equally effective as (visually brighter) white light as an effective treatment of SAD.

Circadian Light Systems
In recent years, the understanding of the physiological mechanism of circadian entrainment has grown significantly. It is rooted in the non-visual physiological responses to light. The visual system is most sensitive to green wavelengths while the non-visual (circadian) system is most sensitive to blue wavelengths.-US Green Building Council (

Since most of us work in buildings, perhaps tucked far away from a window, electric lighting combined with color shifting components are one proposed solution for lack of access to natural light for still supporting circadian entrainment.

Adding to the mix, Ed Clark and Marty Brennan wrote a piece in METROPOLIS outlining “6 Principles for Designing Spaces That Support Circadian Health“. Without paraphrasing all six of their points – and encouraging you to give their piece a read yourself – here are two points they made about light specifically in view of circadian rhythm: