Daylight factor

Daylight factor study colour plot

Daylight factor (DF) is a metric used in architecture and building design to quantify the amount of daylight available in an indoor space. It is expressed as a percentage and represents the ratio of the indoor illuminance at a specific point to the outdoor illuminance under overcast sky conditions. The daylight factor is a crucial parameter in daylighting design, as it helps in assessing the natural light levels within a building, which can impact both the visual comfort and energy efficiency of the space.

Calculation

The daylight factor is calculated using the formula:

DF = (Ei / Eo) * 100

where:

• Ei = Indoor illuminance at a specific point
• Eo = Outdoor illuminance under overcast sky conditions

The daylight factor can be further broken down into three components:

• Sky component (SC): The direct light received from the sky.
• Externally reflected component (ERC): The light reflected from external surfaces.
• Internally reflected component (IRC): The light reflected from internal surfaces.

Importance in Building Design

A higher daylight factor indicates a greater amount of natural light entering the space, which can reduce the need for artificial lighting and improve occupant well-being. Proper daylighting design can lead to:

• Enhanced visual comfort
• Reduced energy consumption
• Improved mood and productivity of occupants

Recommended Values

The recommended daylight factor values vary depending on the type of space and its intended use. For example:

• Residential spaces: 1-3%
• Offices: 2-5%
• Classrooms: 3-5%

Factors Affecting Daylight Factor

Several factors influence the daylight factor in a building, including:

• Window size and placement
• Type of glazing
• Reflectance of interior surfaces
• Presence of obstructions (e.g., neighboring buildings, trees)

Measurement and Simulation

Daylight factor can be measured using a lux meter or simulated using various software tools such as Radiance and DIALux. These tools help in predicting the daylight performance of a building during the design phase.

Related Concepts

• Daylighting
• Illuminance
• Luminous efficacy
• Building energy efficiency
• Visual comfort

See Also

• Daylighting
• Illuminance
• Luminous efficacy
• Building energy efficiency
• Visual comfort