Daylight Factor Calculator

Daylight Factor Formula:

\[ DF = \frac{\text{Indoor Illuminance}}{\text{Outdoor Illuminance}} \times 100\% \]

Daylight Factor (DF):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Daylight Factor?

Daylight Factor (DF) is a metric used in architecture and building design to quantify the amount of natural light available indoors relative to the outdoor illuminance. It represents the percentage of outdoor light that reaches a specific point inside a building.

2. How Does the Calculator Work?

The calculator uses the Daylight Factor formula:

\[ DF = \frac{\text{Indoor Illuminance}}{\text{Outdoor Illuminance}} \times 100\% \]

Where:

\( DF \) — Daylight Factor (%)
\( Indoor Illuminance \) — Light level measured indoors (lux)
\( Outdoor Illuminance \) — Light level measured outdoors (lux)

Explanation: The formula calculates the ratio between indoor and outdoor illuminance, expressed as a percentage to indicate how much natural light penetrates the building interior.

3. Importance of Daylight Factor Calculation

Details: Daylight Factor is crucial for sustainable building design, energy efficiency, occupant comfort, and meeting building code requirements. It helps architects optimize window placement, room dimensions, and building orientation.

4. Using the Calculator

Tips: Enter both indoor and outdoor illuminance values in lux. Measurements should be taken simultaneously under overcast sky conditions for accurate results. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical Daylight Factor values?
A: 2-5% is considered good daylighting, below 2% indicates poor daylight, and above 5% suggests excellent natural lighting conditions.

Q2: When should illuminance measurements be taken?
A: Ideally under overcast sky conditions to eliminate direct sunlight effects, and measurements should be taken at the same time for both indoor and outdoor readings.

Q3: What factors affect Daylight Factor?
A: Window size and orientation, glass transmittance, room geometry, external obstructions, surface reflectances, and internal partitions.

Q4: Are there building standards for Daylight Factor?
A: Yes, many green building certifications (LEED, BREEAM) and building codes specify minimum Daylight Factor requirements for different room types.

Q5: Can Daylight Factor be used for artificial lighting design?
A: Yes, it helps determine when artificial lighting is needed and supports the design of daylight-responsive lighting control systems.