daylight factor

The amount of daylight received in an internal space can be analyzed by undertaking a Daylight factor calculation.

Calculating daylight factors requires complex repetition of calculations and thus is general undertaken by a proprietary computer software product such as Radiance.

A daylight factor is the ratio of internal light level to external light level and is defined as follows:

In order to assess the effect of a poor or good daylight factor, one might choose to compare the results for a given calculation against published design guidance.

The amount of daylight received into an indoor space or room is defined as a daylight factor, being the ratio between the measured internal and external light levels.

The redevelopment of central areas (1946) gave to the new planning authorities a fresh kit of tools, including use-classes, plot ratios, daylight factors, sight lines and parking standards.

In the UK this is likely to be CIBSE Lighting Guide 10 (LG10-1999) which broadly bands average daylight factors into the following categories:

The design day used for daylight factor calculations is based upon the Standard CIE overcast Sky for 21 September at 12:00pm, and where the Ground Ambient light level is 11921 Lux.

Daylight factors are used in architecture and building design in order to assess the internal natural lighting levels as perceived on the working plane or surface in question, in order to determine if they will be sufficient for the occupants of the space to carry out their normal duties.