Daylighting

Daylighting is the practice of using natural light to illuminate interior spaces. It combines building design, glazing, and light-control strategies to provide useful illumination while managing heat and glare.

Daylight factor: The ratio of indoor illuminance at a point to simultaneous outdoor illuminance under a standard overcast sky. It measures how effectively a design brings diffuse daylight into an interior.
Daylight autonomy: The percentage of occupied time that a location meets a specified illuminance threshold using daylight alone. It estimates how often a space can meet lighting needs without electric lights.
Illuminance: The luminous flux incident on a surface per unit area, measured in lux. Daylighting is commonly assessed by the illuminance it delivers to work surfaces.
Electric lighting: Illumination produced by electrically powered light sources. It supplies controllable light when daylight is insufficient or unavailable.
Lighting energy use: The electrical energy consumed by lighting systems in buildings or other settings. Reducing this demand is a direct potential benefit of replacing electric light with daylight.
Visible transmittance: The fraction of visible light that passes through a glazing material. It helps determine how much daylight reaches the room through windows.
Daylight harvesting: The use of sensors and controls to reduce electric lighting when daylight is available. It turns available daylight into lower electric-lighting demand.
Luminance: The amount of light emitted or reflected from a surface in a given direction per unit area. Brightness contrasts between windows and interiors strongly affect visual comfort.
Tubular daylighting device: A roof-mounted daylight collector connected to an interior diffuser by a reflective tube. It brings daylight into rooms where conventional windows or skylights are impractical.
Building energy simulation: Computer modeling of a building's energy use under specified weather, occupancy, and operating conditions. Integrated simulations reveal how daylight, lighting controls, and cooling loads interact.

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