Daylight Modelling

All three measure natural light but in fundamentally different ways, and each serves a different compliance purpose.

Daylight Factor (DF) uses a standardised uniform overcast sky (10,000 lux) to measure the ratio of indoor illuminance to outdoor illuminance. Sun position, orientation, and climate play no part. It is a static threshold check used in ESD reports and planning submissions.

Spatial Daylight Autonomy (sDA) is a climate-based dynamic metric that models all sky conditions throughout the year - overcast, partly cloudy, and clear sky with direct sun. sDA does not exclude direct sunlight; it incorporates all light sources based on real local weather and sun angle data for your location. It measures what percentage of occupied floor area receives sufficient light (160 lux for at least 80% of annual occupied hours).

Sunlight Analysis measures only direct beam sunlight from the sun disc. It calculates how many hours a habitable room or open space receives direct sun on a specific date (typically winter solstice, 9am to 3pm). Diffuse sky light is not counted. Sunlight Analysis is used for Housing SEPP compliance in NSW and is a separate service to daylight modelling.

DF is a steady-state metric that measures the proportion of indoor illuminance to outdoor illuminance under a standardised overcast sky of 10,000 lux. It does not account for sun position, orientation, or local climate. sDA is a climate-based dynamic metric that models actual sun angles and local weather data, measuring what percentage of occupied floor area receives at least 160 lux for at least 80% of annual occupied hours. DF is used as a minimum threshold check in ESD reports and planning submissions. sDA is required for Green Star IEQ credits and reflects real-world daylight conditions more accurately.

A daylight modelling report is typically required when a project is pursuing Green Star certification with IEQ daylight credits, or when a council or planning authority requests evidence of daylight performance as part of an ESD planning report. It is also used proactively to assess and improve apartment layouts and glazing specifications before construction documentation is finalised.

We use IES VE for climate-based Spatial Daylight Autonomy (sDA) modelling and RadianceIES for Daylight Factor assessments. Both are industry-standard platforms accepted by GBCA for Green Star submissions and by planning authorities for ESD compliance reports.

Yes. Early engagement allows our team to identify underperforming spaces and recommend glazing sizes, reflectance values, orientation adjustments, and shading strategies that improve daylight outcomes before construction documentation is locked.

There is a direct trade-off between daylight performance and thermal performance. Increasing glazing area improves daylight but may increase heating and cooling loads and reduce NatHERS or Section J compliance. Ark Resources can model both simultaneously to find the optimal balance for each project.

A standard daylight modelling report takes 1 to 3 weeks depending on project complexity and the documentation available. Green Star sDA assessments may take 2 to 4 weeks. We provide accurate timelines at project briefing.