Climate Based Daylight Modelling is a relatively new way of assessing the quantity and quality of natural daylight and sunlight a room within a building will receive.

The method is gaining popularity as the preferred way to carry out daylight analysis on new developments thanks in part to the Priority Schools Building Programme (PSBP). The PSBP is a new schools specification guideline favoured by many Local Authority’s throughout the country such as Essex County Council.

The PSBP has a very different approach to daylight design compared with previous building programmes and school design guides. In the past, design for daylight within the learning environment has been a numerical process based on a static overcast sky. The ambition was to deliver a certain percentage of diffuse light into the space (daylight factors) and achieve a degree of uniformity. The PSBP uses Climate Based Daylight Modelling (CBDM) which takes account of the quality and quantity of sunlight and daylight.

Using CBDM in place of daylight factors provides far greater detail about light distribution and intensity which allows the building design to be adjusted to maximise the use of sunlight and daylight.

Actual annual weather data specific to the developments location is used to calculate lux levels and targets can be set which are relative to user needs.

For the PSBP two criteria have been established, Useful Daylight Illuminance (UDI) and Spatial Daylight Autonomy (DA).

UDI is defined as the annual occurrence of illuminances across the work-plane that is within a range considered “useful” by occupants – 100 to 3000 lux. This is subdivided:

  • UDI-s (below 100 lux) where the light would be considered insufficient without electric lighting.
  • UDI-a (100 to 3000 lux) where electric lighting is acceptable and electric lighting wouldn’t be needed for the majority of the day. Achieving a high UDI-a percentage signifies the space is predominantly daylit throughout and glare is controlled.
  • UDI-e (above 3000 lux) where the amount of light would be considered excessive and a source of glare and the blinds would be closed.

The PSBP sets a minimum target of 80% UDI-a for each learning space, sports hall and exam area.

DA is the amount of time a space can expect to reach a target illuminance level on the working plane. This criterion is aimed at delivering an energy efficient space.

The output specification sets a minimum target DA of 50% for each learning space, sports hall and exam area.

At Ecodraw we can produce visual results to quickly and easily show you where in your building you are receiving acceptable or excessive amounts of daylight, and where in the property you will require additional electric lighting.

As well as the visual results of the climate based daylight modelling we can also generate a table of the UDI values for each of the rooms and output the Spatial Daylight Autonomy for each.

Contact us today for more information on how Climate Based Daylight Modelling can improve the design of your building and help you to meet planning permission requirements.