1. What is Daylight Factor?

Definition: Daylight Factor (DF) is the ratio of indoor illuminance to outdoor illuminance, expressed as a percentage.

Purpose: It measures how much natural daylight reaches a point inside a building compared to the light available outside.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( DF \) — Daylight Factor (%)
• \( E_i \) — Indoor illuminance (lux)
• \( E_o \) — Outdoor illuminance (lux)

Explanation: The ratio of indoor to outdoor light levels is multiplied by 100 to convert it to a percentage value.

3. Importance of Daylight Factor

Details: DF helps architects and designers evaluate and optimize natural lighting in buildings, which affects energy efficiency, occupant comfort, and visual performance.

4. Using the Calculator

Tips: Measure indoor illuminance at the point of interest and simultaneous outdoor illuminance under overcast sky conditions. Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a good daylight factor value?
A: Typically, 2-5% is considered adequate for most tasks, with 5% being excellent daylighting.

Q2: When should measurements be taken?
A: Under overcast sky conditions for consistent results, as direct sunlight causes large variations.

Q3: Where should indoor measurements be taken?
A: At the work plane (usually 0.75-0.85m above floor) in the area of interest.

Q4: How does daylight factor relate to building standards?
A: Many green building certifications (LEED, BREEAM) have daylight factor requirements.

Q5: Can I use this for skylight calculations?
A: Yes, but skylights typically produce higher DF values than vertical windows.