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Calcimator

Daylighting Factor Calculator

Calculate the Average Daylight Factor for a room based on window area, glass transmittance, room geometry, and surface reflectance.

Inputs

Results

Daylight Factor (%)

1.06

Window-to-Floor Ratio (%)10%
Estimated Daylight Autonomy (%)21%
Daylight Uniformity (%)81%
Lighting Savings (kWh/yr)106
Total Surface Area (sq ft)1,230
RatingMarginal — supplemental lighting recommended
How to Use This Calculator
  1. Enter Room Width and Depth in feet and the Ceiling Height in feet.
  2. Enter Net Glazing Area in sq ft (total glass area excluding frames).
  3. Enter Glass Transmittance (visible light transmittance from the window spec) and Average Surface Reflectance.
  4. Enter Sky Angle Factor reflecting how much of the sky dome the window sees (0.5 unobstructed).
  5. Review Daylight Factor percentage, Daylight Autonomy, and Lighting Savings in kWh/year.

How the result changes with Net Glazing Area (sq ft)

Net Glazing Area (sq ft)Daylight Factor (%)
50017.62
1,75061.65
3,250114.5
4,500158.54

What each input means

Room Width (ft)
Interior width of the room in feet (parallel to the window wall).
Room Depth (ft)
Distance from window wall to back wall in feet.
Ceiling Height (ft)
Floor-to-ceiling height in feet.
Net Glazing Area (sq ft)
Total net glass area (excluding frames). Multiple windows can be summed.
Glass Transmittance (0-1)
Visible light transmittance of the glass. Clear single pane ~0.85, double low-E ~0.55-0.70.
Avg Surface Reflectance (0-1)
Area-weighted average reflectance of all room surfaces. White walls ~0.7-0.8, medium colors ~0.4-0.5.
Sky Angle Factor (0-1)
Fraction of sky dome visible from window center. Unobstructed = 0.5, tall adjacent buildings = 0.1-0.3.

What each result means

Daylight Factor (%)
Average DF — ratio of indoor to outdoor illuminance on an overcast day.
Window-to-Floor Ratio (%)
Glazing area as a percentage of floor area.
Estimated Daylight Autonomy (%)
Approximate percentage of occupied hours with sufficient daylight (≥300 lux).
Daylight Uniformity (%)
Estimated uniformity based on daylight penetration depth vs. room depth.
Lighting Savings (kWh/yr)
Estimated annual lighting energy savings from daylight harvesting.
Total Surface Area (sq ft)
Sum of all interior surfaces used in the DF calculation.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Room Width (ft) = 15, Room Depth (ft) = 20, Ceiling Height (ft) = 9, Net Glazing Area (sq ft) = 30 = 7 input(s) provided
  2. Calculate Daylight Factor
    Daylight Factor
    1.06 = 1.06
  3. Calculate Window-to-Floor Ratio
    Window-to-Floor Ratio
    10 = 10%
  4. Calculate Estimated Daylight Autonomy
    Estimated Daylight Autonomy
    21 = 21%

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

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