L03: Circadian Lighting Design

(3 points)

INTENT

Support circadian health through interventions using electric lighting. 

SUMMARY

This WELL feature requires projects to provide users with appropriate exposure to light for maintaining circadian health and aligning the circadian rhythm with the day-night cycle. 

ISSUE

Circadian rhythms are kept in sync by various cues, including light which the body responds to in a way that is facilitated by intrinsically photosensitive retinal ganglion cells (ipRGCs), the non-image- forming photoreceptors of the eyes. Humans have evolved to base their circadian rhythms around the natural light-dark patterns associated with daytime and night-time.  Being indoors for extended periods of time often does not provide humans with opportunities for the required amount of exposure to daylight, considering typical indoor electric light levels compared to the amount of light the human body expects to receive outdoors. This impacts the functioning of the circadian system and quality of sleep. Disruption of circadian rhythm has been linked with obesity, diabetes, depression and metabolic disorders. Exposure to light at night has been associated with negative health effects, such as breast cancer, circadian phase disruption and sleep disorders. The circadian response of humans to light is dependent on the light that enters the eye and on factors such as spectral properties of the light, brightness levels, duration and timing of exposure. The circadian system is more sensitive to shorter wavelengths of light, and the sensitivity peaks at 480 nm.

SOLUTIONS

Since ipRGCs are located in the retina of the eye, the light levels entering the eye of the occupant must be considered. While developing lighting design for circadian impact, the light levels must be achieved on the vertical plane, at the eye level of the occupant to simulate the light entering the eye of the user. It is also important to consider the duration of exposure to light as well as the timing of exposure. Stimulating the circadian system at night through exposure to bright light can negatively impact sleep quality.

IMPACT

Indoor light levels can have a larger impact on people than seasonal changes in daylight hours. Supporting the circadian health of users through electric lighting interventions can help maintain a healthy circadian system and improve sleep quality, mood and cognitive functions.

REQUIREMENTS

Part 1

Lighting for the Circadian System (Max: 3 points)

Verified by Performance Test

For All Spaces

Electric lighting is used to achieve light levels shown in the table below as measured on the vertical plane at eye level of the occupant. The light levels are achieved at least between the hours of 9 a.m. and 1 p.m. and may be lowered after 8 p.m. at night:

1. The project meets the following requirements in regularly occupied spaces:

   Option 1		Option 2	Points
   At least 150 EML [136 melanopic equivalent daylight D65]	OR	The project achieves at least 120 EML [109 melanopic equivalent daylight D65] with electric light and at least 2 points in Feature L05: Enhanced Daylight Access.	1
   At least 240 EML [218 melanopic equivalent daylight D65]	OR	The project achieves at least 180 EML [163 melanopic equivalent daylight D65] with electric light and at least 2 points in Feature L05: Enhanced Daylight Access.	3

Note: For workstations, the light levels may be achieved at 45 cm [18 in] above the work plane. 

For spaces without workstations, light levels may be achieved at a height of 140 cm [55 in]. See the Performance Verification Guidebook for more details. Projects pursuing WELL Core or that have spaces that do not have furniture installed prior to Performance Verification may submit an annotated architectural plan indicating furniture layout for documentation review.

Note that light levels are achieved on the vertical plane at eye level to simulate the light entering the eye of the occupant. 

Appendix L1 shows how to calculate the EML of individual light sources.

© International WELL Building Institute