LEED Protocol: Energy and Environmental Efficiency of Buildings
Analysis of LEED Categories and Regulations to Reduce Light Pollution through Lighting Design
LEED (Leadership in Energy and Environmental Design) is the leading international environmental certification system for buildings, developed by the U.S. Green Building Council (USGBC). It applies to a wide range of projects, from new buildings to renovations, from interiors to existing buildings and neighborhoods (via BD+C, ID+C, O+M, ND, Homes). Each system assesses the environmental impact of the project through a modular structure of credit categories, including Sustainable Sites, Energy & Atmosphere, Indoor Environmental Quality, and others. Each category contains mandatory prerequisites and optional credits with points, which contribute to the final level of certification (Certified, Silver, Gold, Platinum).
As far as Lighting Designers are concerned, the key credit is "Light Pollution Reduction", located in the Sustainable Sites (SS) category. It requires limiting uplight emission and dispersion beyond site boundaries (trespass), according to parameters defined by IES TM-15 and the Model Lighting Ordinance (MLO). Lighting Designers must adopt luminaires that comply with the BUG rating system and adhere to the limits defined by the light zone of the site (LZ0–LZ4). Compliance with local regulations, such as UNI 10819 and Italian regional laws, is compatible with LEED certification, but it is necessary to align calculation methodologies and technical criteria. Although LEED is based on American standards, it can also be applied in Europe, provided that the design is well adapted and there is alignment with local regulations.
Analyzing the LEED rating systems (BD+C, ID+C, O+M, ND, Homes), it is highlighted that each of them is designed to meet the specific needs of different types of projects, providing a framework of requirements and credits adapted to the relevant application context. Below is a descriptive list of the main LEED rating systems available:
- LEED BD+C (Building Design & Construction) – Applies to new buildings or major renovations, providing a framework for the sustainable design and construction of the entire building. It includes various subcategories for specific types (New Construction, Core & Shell, Schools, Retail, Hospitality, Data Centers, Warehouses, Healthcare, etc.), but in general concerns the building as a whole, including envelope and systems.
- LEED ID+C (Interior Design & Construction) – Addressed to Interior Design projects and complete fit-outs of commercial interior spaces. It is typically applied in interior renovations or fittings of indoor real estate units (e.g. offices in existing buildings, retail stores in shopping malls, restaurants, etc.), focusing on the sustainability aspects of interior spaces without structural interventions on the entire building.
- LEED O+M (Operations & Maintenance) – Dedicated to existing buildings under management, with the aim of improving their operational performance. It applies to buildings that have already been operational for at least one year, affected by minor retrofit or management optimization interventions, with a focus on maintenance, operating procedures and plant improvements without extensive reconstruction. It includes adaptations for school, retail, hotel buildings, data centers, warehouses, etc.
- LEED ND (Neighborhood Development) – Designed for urban and neighbourhood development projects. It assesses the sustainability of entire urban areas (neighbourhoods, subdivisions) in terms of site choice, urban plan, transport, green infrastructure and connections with the context. It can be applied both in the planning phase (projects not yet built or under construction) and to projects already built, certifying entire neighbourhoods or territorial developments.
LEED for Homes – Specific for the residential sector. It applies to single-family and multi-family dwellings (buildings up to 3-5 storeys, beyond which BD+C is used) and residential complexes, with criteria adapted to the needs of the dwellings. It includes assessments on domestic energy efficiency, indoor quality in homes and communities. (It should be remembered that there is also LEED for Cities and Communities for even larger scales, and LEED Zero and Recertification pathways for zero-emission buildings and for recertifying existing buildings, but such schemes are beyond the main focus on BD+C, ID+C, O+M, ND and Homes).
Key differences: LEED rating systems share a common structure based on prerequisites and credits, but are distinguished by scope and some specific criteria. For example, LEED BD+C assesses the entire construction process and overall building performance, while LEED ID+C focuses solely on interior space fit-out, with criteria focused on interior materials, air quality during construction, and other specific aspects. LEED O+M applies to existing buildings and focuses on management, maintenance, resource consumption, and continuous improvement plans, rather than design choices during construction. LEED ND introduces urban planning criteria, such as location choice, sustainable infrastructure design, public transport, open spaces and walkability, which are not relevant in protocols for individual buildings. LEED Homes is geared towards small dwellings, with in-situ verifications and specific criteria for residential comfort and efficiency, often requiring a provider or Green Rater for inspections. In summary, the choice of rating system depends on the scale and type of project: a new commercial building will follow BD+C, the renovation of an office on the 5th floor will follow ID+C, a program to improve the efficiency of an existing building will follow O+M, an eco-neighborhood will follow ND, while a detached house or apartment building will follow Homes.
To fully understand the crucial role of lighting design in LEED certification, it is important to know that although LEED covers multiple aspects of sustainability, some categories are directly related to lighting. The categories that will follow, such as Sustainable Sites (SS), Energy & Atmosphere (EA) and Indoor Environmental Quality (IEQ), are particularly relevant for lighting designers, as they cover key aspects related to lighting design and its environmental, energy and occupant well-being impacts. The LEED system is divided into thematic areas, each of which contains Prerequisites (mandatory) and Optional Credits (which give points). Prerequisites must be met in order to obtain LEED certification, while Optional Credits allow you to accumulate points to obtain a higher level of certification (Certified, Silver, Gold, Platinum). The categories we will list below are specifically focused on lighting, but it is important to remember that LEED also includes other areas that deal with aspects such as Water Efficiency and Materials & Resources, etc. In detail:
- Sustainable Sites (SS) – Includes the Light Pollution Reduction credit, which is crucial for the lighting designer, as it promotes the use of lighting solutions that reduce the effect of light scattering towards the night sky, preventing light pollution and protecting the surrounding environment. This is a key point in many urban applications and in natural or sensitive environments.
- Energy & Atmosphere (EA) – The Optimised energy performance is a key element, particularly with regard to the energy efficiency of lighting solutions. Improving energy performance, using Renewable energy and the Advanced energy consumption monitoring (Advanced Energy Metering) are areas that directly impact the choice of lighting technologies, such as high-efficiency LEDs and intelligent control systems to reduce consumption.
- Indoor Environmental Quality (IEQ) – In this category, the Interior Lighting (control and quality of interior lighting) and Daylight (natural lighting) credit is directly pertinent to the lighting designer. The aim is to ensure lighting that supports occupants' well-being and productivity by optimising light intensity and quality, visual comfort and contrast, in line with guidelines such as ASHRAE 90.1 and LEED v4.
In addition to these main categories, there are cross-cutting categories: Innovation (IN) – This can be an opportunity for the lighting designer to earn credits for innovative solutions in lighting design, such as the adoption of advanced technologies, eco-friendly designs, or strategies that go beyond standard practices. This can include the integration of circadian lighting systems or solutions that maximize lighting efficiency. Regional Priority (RP) – Recognizes specific credits for solutions that address local challenges. For example, in urban areas with high levels of light pollution, a project could earn credits for implementing low-impact lighting solutions and intelligent light management systems.
Credit structure and scores: In each category, the Prerequisites are mandatory requirements without points (they must be met in order to obtain certification, under penalty of exclusion) – for example the minimum reduction of energy consumption or the management of construction site waste. Credits, on the other hand, are optional: each credit is associated with a score based on environmental importance; the project accumulates points by obtaining as many credits as possible. The total points obtained determine the level of LEED certification achieved: Certified, Silver, Gold or Platinum. For example, in LEED v4 BD+C New Construction, 110 total points are available, and levels are awarded as Certified if at least 40 points are reached, Silver with 50+, Gold with 60+ and Platinum with 80+. The breakdown of points reflects the relative weight of the categories (energy and climate have the greatest weight, followed by transport, sites, water, materials, indoor quality, etc.), in line with the sustainability objectives of the protocol. It is important to note that rating systems for Interiors, O+M, ND and Homes have similar categories but with some differences or slightly different names; for example, LEED ND includes categories such as Smart Location & Linkage and Green Infrastructure instead of SS, while LEED Homes adopts criteria tailored to housing. However, the basic principles (division into thematic areas, use of prerequisites and points credits) remain common to all LEED systems.
"Light Pollution Reduction" credit: in LEED v4 and v4.1 it is part of the Sustainable Sites (SS) category and aims to reduce light pollution, improve access to the celestial vault and protect night visibility, reducing negative impacts on the environment and wildlife. This credit, which in LEED v4 BD+C New Buildings is worth 1 point, focuses on outdoor lighting, limiting the emission of light upwards and beyond the site boundary. In LEED v4/v4.1, the regulation excludes the requirements for indoor lighting at night, which were present in the previous LEED 2009 version. To obtain the credit, the project must comply with certain compliance criteria relating to uplighting and disturbance light beyond the boundary (light trespass) generated by the external luminaires. LEED offers two alternative methods for verifying compliance: one is a prescriptive method that is based on the BUG classification of luminaires, while the other is a photometric calculation method. Both methods require the assignment of a suitable Lighting Zone (LZ) to the project, which varies from LZ0 to LZ4 depending on the context. This classification, developed by IES and the International Dark Sky Association, affects the permissible illuminance limits for each parameter. In detail, LZ0 is intended for natural areas, such as astronomical parks and dark areas, with a maximum limit of 0.5 lux of illuminance, while LZ1 concerns rural areas with low luminance. In LZ2 (suburban areas) the limit rises to 1 lux, and in LZ3 and LZ4 (urban areas) the value is 2 lux and 6 lux respectively.
Method 1 – BUG Rating: Refers to a photometric system to classify luminaires according to three parameters: B (Backlight): Illumination emitted towards the rear boundaries; U (Uplight): Illumination emitted upwards, beyond the horizontal; G (Glare): Potential glare in frontal areas at different angles. For each parameter, the values vary from 0 (no emission) to 5 (very high emission). LEED sets maximum limits for each parameter based on the Lighting Zone and the position of the luminaire in relation to the lighting boundary. For example, in LZ0, U0 (zero uplight) is required, while in LZ4 a maximum of U4 is allowed, which is equivalent to a very limited emission. Method 2 requires a limited percentage of the total flux of each luminaire to be emitted above the horizon, with limits ranging from 0% in LZ0-LZ1 up to 6% in LZ4. For the light trespass, the BUG method sets maximum values for B (backlight) and G (glare), depending on the distance of the luminaire from the site boundary. For example, a street light very close to the boundary (<0.5 times its height) must have B0 in LZ0-1, or B1–B2 in LZ3-4. In addition, for Glare (G), in LZ0-1, G0 is required for luminaires installed near the boundary. In summary, the designer must select luminaires with the appropriate BUG rating (e.g. full cut-off optics with very low B and U to illuminate parking lots near borders), so that the light emitted outside the site is negligible. Lighting design plays a key role in this process: it is essential to choose certified, shielded luminaires with optimised photometric curves, often provided by manufacturers in the technical data sheets according to TM-15, and to orient the luminaires correctly to comply with the limits imposed by the BUG system.
Method 2 – Illuminance Calculations: As an alternative to (or in addition to) the BUG rating, the designer can perform lighting calculations to verify that the vertical illuminance along the site boundary does not exceed certain lux values. These limits are established according to the Lighting Zone and range from 0.5 lux in LZ0-LZ1 to 6 lux in LZ4. Calculations shall be made in vertical planes around the perimeter of the site, with measurement points at intervals of up to 1.5 m, up to a height of 10 m or at the height of the highest projector. The designer shall use photometric software to simulate night-time lighting and ensure that the light spill across the boundary remains within the established limits.
Lighting Boundary: Defines the area where light is allowed to be emitted without contributing to light pollution. To comply with the Lighting Boundary, it is crucial that the lighting emitted does not exceed the limits defined by the BUG rating, which classifies luminaires according to three parameters: Backlight (B), Uplight (U), and Glare (G). When a project borders public roads or other public areas, the light boundary can be extended beyond the site limits, but it is essential that the lighting fixtures are oriented correctly to prevent light from escaping beyond the perimeter of the site. In particular, if a luminaire is mounted on a pole that has a height of 10 metres, the distance between the light boundary and the luminaire should be at least 20 metres and the backlight (light emitted towards the inside of the site) must be oriented inwards, respecting the limits imposed by the BUG rating. This approach, which follows the principles of good lighting design, reduces the dispersion of light to the outside and limits the phenomenon of light trespass. The light trespass occurs when the light emitted by a lighting system invades adjacent properties or unwanted outdoor spaces, causing annoyance or disturbance. To minimize this phenomenon, it is essential to design the orientation of the luminaires in such a way that the lighting remains within the boundaries of the site. The regulations relating to the Lighting Boundary establish specific vertical illuminance limits along the site boundary, defined by the Lighting Zone (LZ), which vary depending on the urban or natural context. For example, in LZ0 (natural areas), the maximum illuminance limit is 0.5 lux, while in LZ4 (urban areas), the limit can be up to 6 lux. These limits are crucial for reducing environmental impact and preserving the quality of the night sky. As for the uplight (the upward light emission), the regulations establish maximum percentages of light emitted above the horizontal, with values ranging from 0% in LZ0 up to 6% in LZ4. These limits are essential to prevent the "sky-glow" effect, which damages the visibility of the night sky and contributes to light pollution. Finally, the choice of luminaries plays a crucial role in complying with these regulations. It is essential to select luminaires with appropriate BUG ratings to contain light output in the appropriate directions. In LZ0, for example, the backlight (B) and uplight (U) must be minimized to prevent light from escaping beyond the site boundary. Correct orientation and the use of shielding technologies are crucial to ensure that lighting remains within the site, respecting the limits of light trespass and Lighting Boundary.
Illuminated signs: The credit imposes a limit on the luminance of indoor-lit outdoor signs (e.g., backlit bins). The luminance must not exceed 200 cd/m² of luminance at night (nits) and 2000 cd/m² during the day. This limit was introduced to avoid excessive glare and direct glow from signs at night.
Exemptions: Some types of outdoor lighting are excluded from the requirements, as long as they are controlled separately from the other lights on the site. These include safety lighting and traffic signalling (traffic lights, traffic signs), artistic or architectural lighting of facades and landscapes (only in LZ3 and LZ4, and in any case switched off from midnight to 6 am), lighting for theatrical purposes (film sets, shows), lighting required by law (such as some street lights), emergency lighting (emergency rooms, hospital helipads) and illumination of the national flag (in LZ2–4) and illuminated interior signs. These exceptions are provided for special situations where it is necessary to have light, or it is not possible to manage it as part of the normal system, without penalizing the LEED project.
LEED v4 vs LEED v4.1: In the LEED v4.1 version, the Light Pollution Reduction credit remains broadly similar, with slightly refined criteria. For example, LEED v4.1 BD+C allows you to follow a simplified illuminance criterion or also use equivalent certifications (such as IDA "Dark Sky Friendly" certification for luminaires) as proof of compliance. In addition, LEED v4.1 has also extended the credit to O+M (Operations & Maintenance) protocols for existing buildings, encouraging the upgrade of existing outdoor lighting systems to reduce light pollution. In general, however, the BUG rating and calculation-based approach remains the standard in both v4 and v4.1.
