Daylight Factor

Indoor Daylight

The foundational indoor daylighting metric

Daylight Factor (DF) is the ratio of indoor illuminance to simultaneous unobstructed outdoor illuminance under an overcast CIE sky. Calculated via Radiance ray-tracing, it is climate-independent and required by BREEAM and most national building regulations.

DL-Light computes DF on any horizontal, vertical, or inclined surface and automatically generates BREEAM-compliant reports. Results are displayed as false-colour maps directly on the SketchUp model.

Radiance ray-tracing for accurate results
Any surface orientation — floor, wall, ceiling
Automatic BREEAM report generation
Climate-independent calculation
Required by BREEAM, BRE guidelines, and EN 17037

Frequently asked questions

What is the Daylight Factor?

The Daylight Factor (DF) is the ratio of indoor illuminance to simultaneous outdoor unobstructed illuminance under a CIE overcast sky, expressed as a percentage. It is the foundational static daylighting metric used by BREEAM, EN 17037 Method 1, and most national building regulations.

What Daylight Factor value is considered good?

A 2% average DF is the traditional threshold for adequate daylighting. EN 17037 Method 1 uses target DF values that vary by latitude and target illuminance level (typically 1.8% to 3.5% for 300 lux at northern European latitudes).

Does DL-Light use Radiance to compute DF?

Yes. DL-Light computes Daylight Factor using Radiance ray-tracing, the validated reference engine for daylighting simulation. Results are validated against CIE 171:2006 test cases.

Going further

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

Daylight Factor

The foundational indoor daylighting metric

Frequently asked questions

Start using Daylight Factor today