Average Design Daylight Factor – A ratio of the internal daylight level of a space to the external daylight level, per unit floor area of the perimeter zone. It is calculated at design stage and is measured as a percentage.
Diffuse Transmittance/ Visual Light Transmittance – Coefficient of daylighting that can be transmitted through a glazing material, which includes the effects of dirt (denoted by Maintenance Factor). The higher the diffuse transmittance, the more daylight will pass through. This is affected by several factors; the number of glass panes in the assembly, coatings and the glazing type (clear or bronzed etc). Tinted glass can reflect a lot of light so that only 10% may pass through. Clear glass may allow 90% light through.
Maintenance Factor –Adjustment for percentage loss of daylighting through dirt on the glazing, compared to clean glazing in Rural/Suburban/Urban environments.
Reflectance – Area weighted average reflectance of internal surfaces (ceiling/floor/walls/windows) depending on their color (light/medium/dark).
Surrounding Features – Buildings, structures, or other obstructions that will reduce the angle of sky and therefore, the amount of daylighting internally.
