This is a legacy version of the WELL Building Standard. Please check the latest version here.

Light at night

Light at night


To provide sleeping spaces free from light intrusion and provide low-light wayfinding options.


Light is the primary zeitgeber, the signal by which the body aligns its internal clock with the external environment. Therefore light at night is a potential hazard as it can disrupt circadian rhythm. It blurs the distinction between day and night, and affects the timing of the sleep-wake cycle. However, complete darkness increases the sensitivity of the eyes, so any lights encountered during activities at night have an amplified disruptive effect.

Part 1
Window Light Elimination

All bedroom windows employ one of the following:
Blackout shades with 0% transmittance and no light gaps on the perimeter.
Operable outdoor shutters with 0% transmittance.

Part 2
Electric Light Elimination

In all bedrooms, the following requirement is met:
All electronics have an option to produce no light.

Part 3
Safe Nighttime Navigation Lighting

The following conditions are met:
Nightlights are installed to provide a safe path from all sleeping areas to the closest bathroom and within the bathroom.
Nightlights are located no higher off the ground than 36 cm [14 inches] to the center of the unit.
Nightlights are motion-activated with a manual off and manual on option.
Nightlights do not emit light at wavelengths below 550 nm.
Each nightlight does not produce more than 15 lumens.