Daylight Factor Calculator
Calculate your daylight factor with our free online tool. Get accurate results instantly. No signup required.
What Daylight Factor Calculator does
The Daylight Factor Calculator determines the ratio of indoor to outdoor illuminance, expressed as a percentage, to assess natural light penetration in architectural design. Users input two lux measurements—indoor and outdoor—to receive a daylight factor value and a practical quality rating. This metric helps evaluate how much available outdoor daylight reaches an interior space, serving as a quick check for room access, occupant comfort, and the potential need for supplemental electric lighting. The tool is designed for immediate use without registration, providing instant results for specified inputs.
How to use the Number Convert Daylight Factor Calculator
- 1
Enter the indoor illuminance measurement in lux
- 2
Enter the simultaneous outdoor illuminance measurement in lux
- 3
Click the calculate button to process the inputs
- 4
View the resulting daylight factor percentage and quality rating
- 5
Use the rating to assess if supplemental lighting may be needed for the space
Best for
Architects, interior designers, and students evaluating early-stage room daylight access and occupant comfort without complex software.
Limitations
- Requires accurate simultaneous indoor and outdoor lux measurements
- Results are estimates dependent on assumed sky conditions and measurement timing
- No unit conversion support; both inputs must be in lux
Daylight Factor Calculator FAQ
- Can I use this tool if I only have approximate outdoor light levels?
- The calculator requires both indoor and outdoor lux values measured at the same time or under the same assumed sky condition for accurate results; using estimated or mismatched values will affect the daylight factor percentage.
- What is considered a good daylight factor for a occupied space?
- A daylight factor around 2% or higher is commonly treated as a useful baseline for many occupied spaces, though the appropriate target depends on room type, task, glazing, obstructions, and local design standards.
- Do I need to convert my measurements to lux before using the tool?
- Yes, both the indoor and outdoor illuminance inputs must be in lux before calculating the ratio; the tool does not support unit conversion.
- How does the tool rate the quality of the daylight factor result?
- The tool provides a practical quality rating alongside the daylight factor percentage to help users quickly assess whether the space may need supplemental electric lighting based on the calculated ratio.