nondaylight

Nondaylight is a term used in architecture and urban design to describe conditions in which natural daylight is largely absent from a space for extended periods due to obstructions such as tall buildings, narrow street canyons, or seasonal shading. It is a descriptive label rather than a standardized scientific metric, used to discuss daylight availability in dense urban contexts and to compare design outcomes.

Origin and usage: The term began appearing in design discourse in the 2010s and is not universally defined. It is often used to highlight a contrast with well-lit, daylight-rich environments, and to raise concerns about occupant comfort, energy use, and urban livability in areas with heavy shading.

Factors and measurement: Nondaylight results from geometry (building height, spacing, street orientation), surface reflectance, and atmospheric conditions. Assessments typically rely on daylight factor calculations, daylight autonomy, or illuminance simulations to estimate hours or percentages of daylight deficiency within a space or along a street canyon. The concept remains informal and context-dependent.

Applications and critique: In planning practice, reducing nondaylight informs designs that incorporate light wells, courtyards, podiums, step-backs, or glazing strategies to improve daylight penetration. Critics note that the term lacks standard definitions and may obscure quantitative analysis when used loosely. See also daylighting, urban canyon, and daylight autonomy as related concepts.