Daylighting – calculation procedures

For all spaces in the building where daylight provision is relevant (these are defined in the defintions for the relevant building areas), calculate the area weighted percentage improvement in daylight (Σ Ai Pi) / (Σ Ai ). Here Ai is the floor area of space i and Pi is the percentage increase in daylight in it. The Σ operator means to sum over all the relevant spaces.

In order to demonstrate compliance with criteria 4 and 5 for an improvement in existing daylighting, for each space, the percentage increase in daylight (Pi) is calculated in one of the following ways:

Where only the window area or glass transmission will increase:

  1. If window area has increased but all other aspects remain the same, Pi = ((increase in glass area)/(original glass area)) x100%.
  2. If glass transmission has increased but all other aspects remain the same, Pi = ((increase in glass transmission)/(original glass transmission)) x100%.

Where many aspects will change (e.g. room size, a combination of reflectance and window size etc.):

  1. Calculate the average daylight factor (ADF) in the space ‘before’ and ‘after’. Pi =( (ADF after – ADF before)/ ADF before) x100%.
  2. Calculate the average illuminance in the space that is exceeded for 2000 hours per year. Pi =( (Average illuminance after – Average illuminance before)/ Average illuminance before) x100%.
This will be amended in the next version of the manual.