Introduced by the U.S. Green Building Council (USGBC) in 1998, LEED (Leadership in Energy and Environmental Design) is one of the world's most widely adopted green building certification systems. It provides a framework for creating healthy, efficient and environmentally responsible buildings.

Purpose of the Daylight Credit

The LEED Daylight Credit is designed to:

• Reduce reliance on artificial lighting
• Enhance occupant comfort and wellbeing
• Support productivity and mood through access to natural daylight

These objectives align with LEED's wider mission of promoting healthy, high-performance buildings.

Projects must demonstrate adequate daylight levels within regularly occupied areas. LEED provides three routes to compliance:

1. Dynamic Simulation (Spatial Daylight Autonomy - sDA 300/50)

This approach uses annual daylight modelling to evaluate daylight availability over time.

Requirements include:

• Minimum 40% sDA across at least 55% of regularly occupied floor area to achieve one point
• Higher performance thresholds can achieve additional points
• Provides a comprehensive assessment of daylight performance throughout the year

2. Illuminance Modelling

This simulation-based approach analyses daylight levels under specified sky conditions.

Requirements include:

• Daylight levels between 300 and 3,000 lux across at least 55% of regularly occupied space
• Glare-controlled spaces may be assessed against modified criteria where appropriate

3. On-Site Measurement

Actual daylight readings can be taken within completed buildings.

Requirements include:

• Illuminance levels between 300 and 3,000 lux
• Measurements taken under defined clear-sky conditions during occupied hours

Embodied Carbon Reduction

LEED v5 also places greater emphasis on embodied carbon and lifecycle thinking.

Projects can achieve credits through:

• Option 1: Whole Building Life Cycle Assessment (LCA): A comprehensive assessment of environmental impacts across the building lifecycle.
• Option 2: Low-Carbon Procurement: Selection of lower-carbon construction materials to reduce overall embodied carbon.
• Option 3: Environmental Product Declarations (EPDs): Use of products supported by verified EPDs, promoting transparency and environmental accountability.

This approach encourages design teams to consider the environmental impact of building materials, including daylighting systems, from manufacture through to end-of-life.

A Brief Look at BREEAM

The Building Research Establishment Environmental Assessment Method (BREEAM) provides a framework for assessing and improving the sustainability performance of buildings.

Within BREEAM, daylighting is addressed through the Health and Wellbeing category, helping project teams create comfortable, productive indoor environments.

Daylight Assessment in BREEAM

BREEAM generally evaluates daylight performance using daylight factor calculations, focusing on:

• Static illuminance levels under overcast sky conditions
• Minimum daylight factor thresholds
• Visual comfort and glare control
• Daylight uniformity
• Window design and external views

While BREEAM's methodology is often considered more prescriptive than LEED's dynamic performance-based approach, both systems share a common objective: creating high-quality indoor environments through effective use of natural daylight.

LEED vs BREEAM: Different Approaches, Shared Goals

Although LEED and BREEAM use different methodologies, both recognise daylighting as an important contributor to:

• Occupant health and wellbeing
• Energy efficiency
• Sustainability performance
• Environmental responsibility
• High-performing building design

For architects, specifiers and building owners, daylighting remains a key strategy for achieving certification objectives while creating more sustainable and enjoyable places to live, learn and work.