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Median Daylight Factor

The median DF gives a robust representation of typical conditions in rooms with uneven daylight distribution — avoiding inflation by very bright areas.

Design quality
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Median Daylight Factor distribution map
Indoor Daylight

Robust DF for uneven spaces

The Median Daylight Factor is the median DF value across a room, rather than the mean. In rooms where a few very bright areas (near windows, rooflights) would inflate the average, the median provides a more representative picture of typical conditions.

Median DF is particularly used in Australian planning assessments and in contexts where regulatory thresholds are based on the distribution of DF rather than the average.

  • Median rather than mean — more robust in uneven spaces
  • Used in Australian planning assessments (SEPP65)
  • Useful for atria, deep floor plans, and top-lit spaces
  • Reduces bias from very bright perimeter zones
  • Part of the core DF module

Frequently asked questions

What is Median Daylight Factor?

Median Daylight Factor (Median DF) is the middle value of daylight factor measurements across a space. It represents typical daylighting performance, less affected by extreme values than average DF and useful for comparative assessment.

How does DL-Light compute it?

DL-Light calculates Daylight Factor at a grid of points across the analyzed surface using Radiance, then computes the median value. This provides a robust central measure of daylighting performance.

What thresholds or standards apply?

Median DF is used in BREEAM daylighting assessment as a reliable measure of overall space performance. Assessment criteria typically compare median DF against minimum targets, providing more stable results than average values.

Going further

Read the full DL-Light user-guide reference for Median Daylight Factor: Windows guide · macOS guide.

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