DesignBuilder Radiance is ideal for calculating daylighting credits for certification schemes such as LEED, BREEAM and Green Star. In these cases there is often pressure to provide highest possible illuminance reports and, because some settings can cause illuminance values to be lower than expected, this section provides advice on the most appropriate settings to use.
Many of the LEED, BREEAM and Green Star daylighting credit calculations revolve around a "% of floor area having daylight illuminance over a threshold" report for each zone and for the whole building. The table below describes how to get the most accurate results from these calculations.
| Setting | Recommended Setting | Advice |
| Detail template | 5-Accurate | You should use the most detailed setting you can afford to wait for. The 1-Fast setting is not intended for project output and should be avoided for all credit calculations as it tends to lead to severe underestimates of illuminance levels. The accuracy increases as the level of detail in the calculation increases up to and including the 5-Accurate setting. The 6-High quality setting is also not recommended for these sort of calculations as it does not add much in terms of accuracy but takes a lot longer than the 5-Accurate setting. |
| Ambient Bounces | 3-8 |
The 5 built in templates are ideal for “simple daylight scenes that have shallow spaces with relatively large window openings”. However in deep plan models or models with small windows or greater external/internal complexity of the model you may want to increase the number of bounces from the default set by the Detail template. Models which have complex exterior geometry may require up to 8 bounces to ensure that the light reflection from exterior building surfaces is correctly treated. Likewise to obtain the correct impact of variations in the floor reflectance you will need to use 5 or more bounces. Tip: If you aren't sure, try experimenting with different values for this setting to test sensitivity and learn impact on results. |
| Grid size |
Max: 0.2m Min: 0.05m |
Of course, the finer the overall grid the more accurate the results. Perhaps less obvious however is that using lower values for Minimum grid size can lead to more accurate and higher zone average illuminance results. This is because the small grid cells generated with the low minimum grid size can fill in around the edges of the working plane where often the highest levels of daylight are to be found. |
| Margin | 0 | Use a zero margin if you need the entire working plane to be included in the results. This will often lead to higher % areas over daylight thresholds because the edges of the working plane are usually closest to where many of the windows are located. |