Circadian lighting design

Circadian lighting design

Intent: 

To support circadian health by setting a minimum threshold for daytime light intensity.

BACKGROUND

Light is one of the main drivers of the circadian system, which starts in the brain and regulates physiological rhythms throughout the body’s tissues and organs, affecting hormone levels and the sleep-wake cycle. Circadian rhythms are kept in sync by various cues, including light which the body responds to in a way facilitated by intrinsically photosensitive retinal ganglion cells (ipRGCs): the eyes’ non-image- forming photoreceptors. Through ipRGCs, lights of high frequency and intensity promote alertness, while the lack of this stimulus signals the body to reduce energy expenditure and prepare for rest. The biological effects of light on humans can be measured in Equivalent Melanopic Lux (EML), a proposed alternate metric that is weighted to the ipRGCs instead of to the cones, which is the case with traditional lux. During Performance Verification, EML is measured on the vertical plane at eye level of the occupant. Tables L1 and L2 in Appendix C show how to calculate the EML of individual lamps and larger spaces.

Part 1
Melanopic Light Intensity for Work Areas

Light models or light calculations demonstrate that at least one of the following requirements is met:
a.
At 75% or more of workstations, at least 200 equivalent melanopic lux is present, measured on the vertical plane facing forward, 1.2 m [4 ft] above finished floor (to simulate the view of the occupant). This light level may incorporate daylight, and is present for at least the hours between 9:00 AM and 1:00 PM for every day of the year.
b.174
For all workstations, electric lights (which may include task lighting) provide maintained illuminance on the vertical plane facing forward (to simulate the view of the occupant) of 150 equivalent melanopic lux or greater.

Part 2
Melanopic Light Intensity in Living Environments

In all bedrooms, bathrooms, and rooms with windows, one or more fixtures provide the following:
a.
200 or more equivalent melanopic lux as measured facing the wall in the center of the room 1.2 m [4 ft] above the finished floor. The lights may be dimmed in the presence of daylight, but are able to independently achieve these levels.
b.
Lights provide not more than 50 equivalent melanopic lux (to the extent allowable by code) as measured 0.76 m [30 inches] above the finished floor.

Part 3
Melanopic Light Intensity in Breakrooms

Workplaces where employees spend most of their time in spaces with light levels limited by work type (such as restaurant servers or hospital ward workers) have break rooms which meet the following requirement:
a.
Lights provide a maintained average of at least 250 equivalent melanopic lux as measured on the vertical plane facing forward at surfaces 1.2 m [4 ft] above finished floor. The lights may be dimmed in the presence of daylight, but are able to independently achieve these levels.

Part 4
Melanopic Light Intensity in Learning Areas

At least one of the following requirements is met:
a.
Early education, elementary, middle and high schools, and adult education for students primarily under 25 years of age: Light models (which may incorporate daylight) show that at least 125 equivalent melanopic lux is present at 75% or more of desks, on the vertical plane facing forward 1.2 m [4 ft] above finished floor (to simulate the view of the occupant). This light level is present for at least 4 hours per day for every day of the year.
b.139
Ambient lights provide maintained illuminance on the vertical plane of equivalent melanopic lux greater than or equal to the lux recommendations in the Vertical (Ev) Targets in Table 3 of IES-ANSI RP-3-13, following the age group category most appropriate for the population serviced by the school. For example, art studios in elementary school, middle school, or high school are provided with 150 equivalent melanopic lux from the electric lights.