Step 1 — Climate

For Concept mode, set your latitude and longitude (or leave at default). For Standard and Advanced, load an EPW weather file from EnergyPlus for your location. Set the North Angle to orient the model correctly — 0° = model Y-axis points North.

Step 2 — Geometry

Define the room dimensions (Length × Width × Height) in the Geometry tab. Set the workplane height (typically 2.5 ft / 0.76 m for US desks) and grid resolution. Finer grids (0.5 ft) are more accurate but slower; 2 ft is a good default.

Step 3 — Apertures

Add windows with wall assignment (N/S/E/W), horizontal offset from the wall corner, sill and head heights, width, and visible transmittance (Tvis). Add skylights with position, size, and well depth. Shading devices (overhangs, fins, light shelves) can be attached per window.

Step 4 — Materials

Set surface reflectances for ceiling, walls, floor, window reveals, and light shelves. These strongly affect the internally-reflected component of DF and illuminance. Typical values: ceiling 0.80, walls 0.55, floor 0.25.

Step 5 — Run Analysis

Click Run Analysis. Results appear in the right panel and the spatial grid auto-selects the DF map. Switch metrics using the chips in the colour legend (fc, DF%, sDA, ASE, UDI, UGR, eDGP).

Step 6 — Export

Use the Export view tab to download CSV files for workplane illuminance, sDA/ASE/UDI compliance grids, or project JSON for later reload.

3D View

Shows the room in perspective with wall thickness, windows with reveal depth, shading devices, and the workplane heatmap projected onto the floor plane. Drag to orbit; scroll to zoom. Use the corner buttons to reset the camera, toggle wireframe, or toggle the heatmap overlay.

Plan View

Top-down orthographic view of the workplane grid. Best for reading spatial distributions of sDA, ASE, UDI, and glare maps. Min/max values are printed in the lower corners.

Section View

Vertical cut through the room showing the section geometry with wall thickness, windows, shelves, and workplane line. Below the section drawing, an illuminance (or DF) profile chart plots values along the cut at the current section position.

• N–S section: cut plane parallel to the Y-axis at a fixed X position. The profile chart shows values from south wall (Y=0) to north wall.
• E–W section: cut plane parallel to the X-axis at a fixed Y position. The profile chart shows values from west (X=0) to east.

Drag the Position slider in the section overlay to move the cut plane.

Time Navigator

The slider below the Section view scrubs through all 8,760 hours of the year. This updates the sun arc in the 3D view and the section illuminance drawing in real time (Standard/Advanced only).

Daylight Factor (DF%) All modes

The ratio of interior illuminance to simultaneous unobstructed exterior horizontal illuminance under a CIE Standard Overcast Sky, expressed as a percentage. DF is independent of orientation and time of year. Target: ≥2% for offices, ≥5% for living spaces.

Illuminance (fc) All modes

Instantaneous horizontal illuminance at workplane height in footcandles. In Concept mode this is derived from DF (DF% × 500 lux outdoor ÷ 10.764). In Standard/Advanced it is the climate-weighted annual mean.

sDA — Spatial Daylight Autonomy S A

Percentage of the floor area that receives at least 300 lux for at least 50% of occupied hours per year. LEED v4 credit requires sDA ≥ 55% (Option 2) or ≥75% (Option 1, no ASE penalty).

ASE — Annual Sunlight Exposure S A

Percentage of the floor area that receives more than 1,000 lux of direct sunlight for more than 250 occupied hours per year. ASE measures glare and overheating risk. LEED v4 requires ASE ≤ 10%.

UDI — Useful Daylight Illuminance All modes

Fraction of occupied hours when illuminance falls within a useful range (typically 100–3,000 lux). Values split into: Below (too dim), Useful (target zone), and Excessive (potential glare).

UGR — Unified Glare Rating A

Perceptual glare index based on window luminance, solid angle, and background luminance. Scale: 5 (imperceptible) to 38 (intolerable). Target: UGR ≤ 19 for office tasks (EN 12464-1).

eDGP — Enhanced Simplified DGP A

Annual fraction of occupied hours when daylight glare probability exceeds the perturbed threshold (DGP > 0.35). Target: ≤5% perturbed hours for imperceptible glare conditions.

Design Strategies

• Window-to-Wall Ratio (WWR): A south-facing WWR of 30–40% typically achieves sDA ≥ 55% without excessive ASE in temperate climates. Higher WWR increases glare risk.
• Light shelves: Redirect high-angle light deeper into the room, improving DF uniformity. Optimal interior depth is 1.5–2× the shelf height above the workplane.
• Overhangs: Reduce ASE on south windows without significantly reducing sDA. Projection factor = depth ÷ (head height – sill height) of 0.5–0.7 is typical for US latitudes.
• Ceiling reflectance: The single most impactful material property for DF. Raising ceiling reflectance from 0.5 to 0.8 can increase average DF by 15–25%.
• Room depth: The useful daylit zone typically extends 2–2.5× the window head height from the façade. Rooms deeper than this will have low sDA near the back.

Keyboard Shortcuts

Sky Model Concept

Uses the CIE Standard General Overcast Sky (Type 1) — a diffuse, isotropic overcast dome with luminance proportional to (1 + 2 sinγ)/3, where γ is the solar altitude. The standard reference illuminance is 10,000 lux (929 fc) on an unobstructed horizontal plane.

Daylight Factor Calculation

DF is computed using a simplified BRE/Littlefair split-flux method:

• Direct sky component (SC): The fraction of the sky dome directly visible from each grid point through each aperture, weighted by sky luminance distribution.
• Externally reflected component (ERC): Light reflected from the ground plane (ρ = 0.20) and external obstructions visible through the window.
• Internally reflected component (IRC): Diffuse inter-reflection from room surfaces, computed using the area-weighted mean reflectance formula: IRC = Awin × Tvis × ρ_avg / (Atotal × (1 − ρ_avg)).

An inter-reflection boost factor of 1 + ρ_avg × 0.85 is applied to account for multiple reflections. Results carry an estimated uncertainty of ±18% relative to Radiance reference calculations.

Illuminance Conversion

Concept-mode fc values are derived as: fc = (DF% / 100) × 500 lux / 10.764, where 500 lux is a representative overcast outdoor illuminance for early-stage sizing.

UDI Computation

In Concept mode, UDI is estimated from the window-to-wall ratio and room geometry using regression curves calibrated against parametric Radiance runs. The useful band is 100–3,000 lux (9.3–279 fc).

Sky Model Standard

Annual simulation using hourly EPW weather data. Each occupied hour generates a sky luminance distribution using the Perez all-weather sky model parameterised from direct normal irradiance (DNI) and diffuse horizontal irradiance (DHI) in the EPW file. Default occupancy: 08:00–18:00, all weekdays (2,600 h/yr).

sDA Calculation

For each grid point, the hourly illuminance is computed using daylight coefficients pre-calculated from the CIE sky patches. sDA is the fraction of points with illuminance ≥ 300 lux (≈28 fc) for ≥50% of occupied hours. Threshold and occupancy schedule are user-configurable in Advanced mode.

ASE Calculation

Direct sunlight illuminance is computed separately from the diffuse component using sun direction vectors. ASE counts hours where direct illuminance exceeds 1,000 lux (93 fc) at each grid point. The spatial map shows annual direct sun hours (0–250 h), anchored to the aggregate ASE% from the simulation.

DF in Standard Mode

DF is computed using the same split-flux method as Concept mode, but with the full geometric model (all windows, skylights, obstructions, shading devices) and refined material data. Uncertainty is reduced to ±8% relative to Radiance.

Occupied Hours

Simulation Engine Advanced

Advanced mode uses a 3-phase daylight coefficient (DC) matrix method equivalent to the Radiance/DIVA workflow: a view matrix (V) maps grid points to sky patches, a daylight matrix (D) maps sky patches to window apertures, and a transmission matrix (T) accounts for glazing. The combined VTD matrix is pre-computed once and convolved with the annual sky vector.

Glare Calculation — UGR

Unified Glare Rating is computed at each grid point using the CIE 117:1995 formula:

UGR = 8 log₁₀ [ (0.2 / Lb) × Σ(Ls² × ω / p²) ]

where Lb is background luminance, Ls is source luminance, ω is solid angle subtended, and p is Guth position index. Peak and P90 values are extracted from the spatial map.

Glare Calculation — eDGP

Enhanced Simplified Daylight Glare Probability (Wienold 2009):

eDGP = 5.87×10⁻⁵·Ev + 9.18×10⁻²·log₁₀(1 + ΣLs²·ω / Ev^1.87) + 0.16

The annual fraction of occupied hours above DGP = 0.35 is reported as the perturbed hours percentage. Glare categories follow Wienold & Christoffersen (2006): imperceptible (<0.35), perceptible (0.35–0.40), disturbing (0.40–0.45), intolerable (>0.45).

DF in Advanced Mode

The DC matrix method produces per-point DF values with the highest precision (±3% vs. Radiance reference). The annual climate sky is not used for DF — it uses the CIE overcast sky for strict comparability with Concept and Standard modes.

Variance Analysis

A second pass adds Monte Carlo variance analysis on surface reflectances (±5%) and Tvis (±3%) to produce confidence intervals for sDA and eDGP. Results represent the median estimate from 50 samples.

Known Limitations

• Rectangular rooms only: L-shaped, irregular, or multi-zone spaces are not supported. Complex geometry should be modelled in Radiance or EnergyPlus.
• Single-zone model: Adjacent rooms, corridors, and inter-zone daylight transfer are not modelled. Each room is treated as isolated with opaque boundaries.
• Far-field obstructions only: External obstructions are modelled as blocking objects at distance; self-shading between buildings is approximated by sky view factor reduction.
• No electric lighting: Results represent daylight-only conditions. Combined daylight + electric lighting analysis requires integration with a lighting energy tool.
• Flat terrain: Ground reflectance is uniform at ρ = 0.20. Sloped sites, water bodies, and snow are not modelled.
• Diffuse glazing excluded: Fritted, translucent, or prismatic glazing is modelled only by its effective Tvis. Angular-dependent transmission (BSDF) requires the full Radiance workflow.
• Thermal mass not considered: The model produces optical outputs only. Thermal performance, solar heat gain coefficient (SHGC), and U-value are not calculated.

Validation

The split-flux and DC matrix methods have been validated against Radiance 5.3 and DIVA 4.0 reference simulations for rectangular single-zone rooms with south-facing fenestration. Mean bias error (MBE) for average DF is <8% for Concept and <3% for Advanced. sDA and ASE deviations are within ±5 percentage points for typical WWR ranges (15–45%).