Evidence-based design has taught us a lot about the importance of lighting, particularly daylighting, in the healing process. Faster recovery times, less pain, and a general sense of well-being have been connected with patient access to daylight.

Anecdotally, most everyone feels more spring in their step on sunny days than on cloudy ones. There’s also a greater sense of safety during the day, and in well-lit places versus unlit ones at night. We fear what we can’t see. The contrast is even allegorical: Goodness is associated with light, while someone named The Prince of Darkness is surely evil.

Light is important to all people in how it assists in regulating our body clocks, affecting chemical processes in our brains, and supporting a healthy metabolism. What’s not to like about light?

Well, it turns out that darkness is just as important. We need it to be healthy, too! Only in darkness will certain critical body functions take place.

The optic nerves in our eyes sense light; this is true even if we don’t see it. Even absent visual receptors—for example, in people who are blind—when light is sensed, a signal is sent to the brain that it’s time to wake up. Cortisol levels rise, melatonin production drops, and our bodies prepare for action.

When this happens at night—when we’re supposed to be sleeping—we lose some of the restorative benefits of sleep. Research has shown that this can have deleterious effects on body fat levels, systemic inflammation, and insulin resistance. Melatonin, which is produced when it’s dark, lowers blood pressure, body temperature, and glucose levels.

Light at night disrupts our bodies’ normal cycles, and has a negative effect on our health. We should be sleeping in total darkness.

There’s no argument that sleep is essential to the recovery process. The Centers for Medicare & Medicaid Services seems to acknowledge this with a question on the HCAHPS survey, which asks patients how often the area around their room was quiet at night. Partly because of this question, architects are devising more ways to make patient rooms quieter.

Yet there is no question in the HCAHPS survey about whether your room was dark at night. Think about all of the sources of unwanted light at night that may be present in a patient room: displays on patient monitors and other medical devices; spill light from the corridor, and perhaps from outdoors; the night light; that annoying little blue light on the TV that you aim the remote at.

Can we as architects design ways to darken patient rooms at night? Successful patient outcomes may depend on it.

Joan Suchomel is president of the AIA Academy of Architecture for Health and is a principal at Eckenhoff Saunders Architects (Chicago). She can be reached at jsuchomel@esadesign.com. She would like to thank lighting designers Michael White and Giulio Pedota of Schuler Shook for their assistance with this blog.