Why are BREEAM Annual Daylighting Results Different from sDA and UDI?

In general, BREEAM annual daylighting results for HEA-01 Visual Comfort are not comparable to other apparently equivalent calculations such as sDA and UDI. This is because the acceptance criteria method used is different.

By default the sDA results map show sample points that maintain over 300 lux for more than 50% of the year, but these thresholds can be changed to values that may seem to correspond to what BREEAM requires. However, BREEAM works differently.

BREEAM states in HEA 01 Table 12 that "both criteria (average illuminance and minimum point illuminance) should be met". Specifically, both the “minimum daylight illuminance at the worst lit point” must be over the minimum illuminance threshold and also "Average daylight illuminance (averaged over entire space)" must be over the average illuminance threshold. See:

BRE Website BREEAM Technical Manual New Construction Hea 01 Visual comfort

The worst lit point, however, changes from hour to hour. That is to say, at any given hour, if one of the sample points is under the “minimum daylight illuminance at the worst lit point” threshold then that hour is flagged as a "fail".

Another way to think about this is for BREEAM, every cell must be over the lux threshold for at least the target number of hours.