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Daylight and Sunlight Analysis Explained

Daylight affects how a space feels and how much energy it uses. Analysis turns that into something you can test.

Daylight and sunlight affect wellbeing, energy use and planning decisions. Analysis helps Architects design spaces with good daylight and assess impacts on neighbouring buildings.

Daylight vs sunlight

• Daylight: diffuse light from the sky
• Sunlight: direct light from the sun

They're assessed in different ways.

Common metrics

• Daylight factor: the ratio of indoor to outdoor illuminance under an overcast sky
• Vertical sky component (VSC): how much sky is visible from a window
• No-sky line: the area of a room that can't see the sky
• Climate-based metrics: such as spatial daylight autonomy, using weather data
• Sunlight hours: how much direct sunlight a window or space receives

UK guidance

In the UK, the BRE guide "Site layout planning for daylight and sunlight" (BR 209) is widely used in planning assessments of neighbour impacts. BS EN 17037 sets out a European approach to daylight in buildings, and the BRE guide's latest edition refers to it for new spaces. Local planning authorities decide how guidance is applied.

Other regions

In the US, certification systems such as LEED include daylight credits using climate-based metrics. In the UAE, green building regulations may include daylight-related requirements. Check the applicable rules.

Neighbour impacts

Planning applications in the UK often need daylight and sunlight assessments for neighbours, checking changes in VSC and sunlight.

Modelling inputs

• Accurate geometry, including surrounding buildings
• Window sizes and positions
• Glazing light transmittance
• Surface reflectances
• Location and orientation

Tools

Tools range from simple plugins to specialist software. Choose tools appropriate to the assessment.

Balancing daylight and heat

More glazing improves daylight but may increase overheating or heat loss. Balance daylight with thermal performance.

Early design

Early checks help set window sizes and layouts before detailed assessment.

Specialist assessments

Formal assessments, especially for planning, are often done by specialist consultants.

Common mistakes

• Leaving out neighbouring buildings or trees
• Using unrealistic surface reflectances
• Ignoring frame and glazing bar sizes
• Mixing up metrics from different guidance

Checking inputs avoids misleading results.

1. 01Daylight vs sunlight
2. 02Common metrics
3. 03UK guidance
4. 04Other regions
5. 05Neighbour impacts
6. 06Modelling inputs

Reporting

Daylight and sunlight analysis supports healthier, better-lit buildings and smoother planning.

If your team needs extra production capacity for work like this, take a look at our Architectural production services, or tell us about your project.