Understanding BUG Rating
When dealing with dark sky ordinances, or just to protect the environment and night sky visibility, a crucial factor to consider is BUG Rating. The Illuminating Engineering Society (IES) and DarkSky developed BUG Ratings to classify outdoor light fixtures to minimize light pollution. BUG stands for Backlight, Uplight, and Glare. The BUG rating system was developed by the Illuminating Engineering Society (IES) and the International Dark Sky Association. To understand BUG Ratings and to know how they are used in an outdoor lighting project, we first need to know what a Lighting Zone is, and then what the BUG in BUG ratings stands for.
Lighting Zones (LZ) are classifications that determine how much light, as well as how much up-light, backlight, and glare are acceptable in a location. Each LZ has a list of acceptable BUG ratings. The luminaire classification system evaluates outdoor light fixtures based on their backlight, uplight, and glare emissions.
BUG Ratings report the backlight (B), up light (U), and Glare (G) for an outdoor light fixture. For an outdoor light fixture to be permitted or appropriate in a lighting zone, the BUG Rating must be below the specified parameters. The BUG rating is a comprehensive system for all outdoor lighting, replacing the original cutoff system that applied solely for street lighting. The bug system divides light emissions into subzones for assessment, providing a structured method for evaluating stray light.
Key Takeaways
-
-
The BUG rating system, developed by the Illuminating Engineering Society (IES) and the International Dark Sky Association (IDA), is a vital tool for evaluating outdoor light fixtures based on their backlight, uplight, and glare emissions, helping to minimize light pollution and improve lighting quality.
-
Understanding and adhering to lighting zones and BUG rating thresholds ensures that outdoor lighting projects comply with local regulations, reduce unwanted light trespass, and protect the night sky and the surrounding environment.
-
Incorporating BUG ratings into lighting design promotes energy efficiency, visual comfort, and environmental sustainability, making it essential for lighting professionals and property owners aiming for responsible and effective outdoor lighting solutions.
-
Introduction to Light Pollution
Light pollution is an increasingly pressing issue that affects communities, ecosystems, and our ability to enjoy the night sky. Defined as excessive or misdirected artificial light at night, light pollution disrupts natural cycles, impacts wildlife, and obscures our view of stars and celestial events. The International Dark Sky Association (IDA) has been instrumental in raising awareness about these problems and advocating for responsible lighting practices worldwide. One of the most effective tools in this effort is the BUG rating system, which evaluates outdoor light fixtures based on their backlight, uplight, and glare (BUG) emissions. By understanding how light fixtures contribute to stray light, glare, and unwanted backlight, we can make informed choices that help limit light pollution. Opting for outdoor lighting with a low BUG rating ensures that light is directed only where it’s needed, reducing the amount of light escaping into the environment and preserving the natural beauty of the night sky for everyone.
What are Lighting Zones and Why Do Lighting Zones Matter?
A Lighting Zone is usually specified by regulation, and if not regulated, may be determined by preference. LZs define the purpose or function of a location using letters and numbers of LZ-0 through LZ-4. Each LZ has a listed maximum backlight, up light, and glare rating. To determine if a light fixture is qualified to be in a given LZ, determine the LZ number. Then check if the light fixture’s BUG rating is less than the maximum allowable backlight, up light, and glare for the LZ. Backlight ratings are used in standard tables to ensure compliance with lighting boundaries and glare control, helping to minimize light pollution from outdoor luminaires. Remember that BUG may only be one part of the regulations for the LZ. Light trespass requirements are also a key consideration in exterior lighting regulations.
List and Description of the 5 Lighting Zones
- Lighting Zone 0 should be applied to areas in which permanent lighting is not expected, and when used, it is limited in the amount of lighting and the period of operation. LZ-0 typically includes undeveloped areas of open space, wilderness parks, and preserves, areas near astronomical observatories, or any other area where the protection of a dark environment is critical. A special review should be required for any permanent lighting in this zone. Some rural communities may choose to adopt LZ-0 for residential areas.
- Lighting Zone 1 pertains to areas that desire low ambient lighting levels. These typically include single and two-family residential communities, rural town centers, business parks, and other commercial or industrial/ storage areas, typically with limited nighttime activity. May also include the developed areas in parks and other natural settings.
- Lighting Zone 2 pertains to areas with moderate ambient lighting levels. These typically include multifamily residential uses, institutional residential uses, schools, churches, hospitals, hotels/motels, commercial and/or business areas with evening activities embedded in predominantly residential areas, neighborhood-serving recreational and playing fields, and/or mixed-use development with a predominance of residential uses. Can be used to accommodate a district of outdoor sales or industry in an area otherwise zoned LZ-1.
- Lighting Zone 3 pertains to areas with moderately high lighting levels. These typically include commercial corridors, high-intensity suburban commercial areas, town centers, mixed-use areas, industrial uses, and shipping and rail yards with high nighttime activity, high-use recreational and playing fields, regional shopping malls, car dealerships, gas stations, and other nighttime active exterior retail areas.
Access Fixtures Case Study - Lighting Project in Villa Palazzo Considering Light Trespass
- Lighting Zone 4 pertains to areas with very high ambient lighting levels. LZ-4 should only be used for special cases and is not appropriate for most cities. LZ-4 may be used for extremely unusual installations such as high-density entertainment districts and heavy industrial uses.
For certain applications and lighting zones, selecting the appropriate fixture type is essential to ensure proper light distribution and compliance with BUG rating requirements. Fixture types such as Type I, Type II, Type III, Type IV, and Type V are designed to address specific distribution patterns and application needs within each lighting zone. Choosing the correct type helps optimize performance and meet regulatory standards.
An Overview of BUG Rating
BUG ratings enable people to make an informed decision about how appropriate a light fixture is for various outdoor applications and locations. The overall rating for a fixture is determined by the highest subcategory rating among backlight, uplight, and glare, meaning the highest value in any of these categories sets the overall rating. Using light fixtures with lower BUG ratings reduces unnecessary light pollution and promotes a more sustainable approach to outdoor lighting.
When planning an outdoor lighting project, understanding BUG ratings can help ensure compliance with local regulations and minimize light pollution.
What is BUG Rating?
BUG Rating, also known as Backlight-Uplight-Glare Rating, is a system that evaluates and specifies the optical performance of outdoor light fixtures. Developed by the Illuminating Engineering Society (IES), the BUG rating assesses the impact of a luminaire’s backlight, uplight, and glare characteristics on its overall performance and efficiency.
BUG ratings focus on 3 main components:
- Backlight (B): This rating is related to the amount of light escaping from the luminaire in the rearward direction.
- Uplight (U): This rating deals with how much light is emitted in the upward direction from the luminaire, which may contribute to light pollution. Uplight is the light that shines upwards from a fixture towards the sky, contributing to light pollution, and the uplight rating (U rating) measures this component. The uplight rating, also referred to as the U rating, categorizes luminaires based on the amount of light emitted upward, with specific U ratings (U0 to U4) assigned according to lumen thresholds in various subzones.
- Glare (G): This rating considers the amount of visual discomfort caused by glare from the luminaire to an observer in different positions. Glare is the light that shines directly into people's eyes, making it difficult to see and creating safety risks.
The purpose of the BUG rating system is to ensure that lighting fixtures meet the requirements for proper illumination and energy efficiency while considering their environmental impact.
The BUG rating system is used to achieve the following objectives:
- Minimize light pollution by minimizing uplight and glare from exterior lighting systems.
- Evaluate and compare different luminaires before installation to ensure that you meet local, state, and possibly national lighting guidelines and regulations.
- Improve the overall efficiency and performance of your lighting systems by choosing luminaires that have better optical control and lower energy consumption.
Understanding and utilizing the BUG rating system is essential for making informed decisions about lighting projects. It ensures that the project meets the necessary guidelines and requirements for energy efficiency, visual comfort, and environmental sustainability.
Shop LED Bollard Lights with Optional Shielding to Prevent Light Trespass
Benefits of the BUG Rating System
The BUG rating system brings a host of benefits to outdoor lighting design and environmental stewardship. By providing a clear, standardized way to assess the backlight, uplight, and glare produced by light fixtures, the system empowers lighting professionals and property owners to select products that minimize light pollution and light trespass. Fixtures with low BUG ratings are specifically engineered to reduce wasted light, prevent glare, and keep light from spilling onto neighboring properties or into the sky. This not only enhances lighting quality and visual comfort for people using outdoor spaces, but also supports energy efficiency by ensuring that every lumen is put to good use. Municipalities and lighting designers rely on the BUG rating system to develop lighting plans that meet local safety requirements and regulations, while also protecting the environment and maintaining the integrity of the night sky. Ultimately, the BUG rating system is a key tool in achieving high-quality, sustainable outdoor lighting that benefits both people and the planet.
BUG Rating Components
We now know that BUG Ratings report the backlight (B), up light (U), and Glare (G) for an outdoor light fixture, but why are these measured and reported? Why is every BUG Rating component relevant? Glare is further divided into glare subzones, which are rated on a scale from 0 to 5 to assess overall light pollution and safety standards. Additionally, the lumens emitted in each zone are measured to determine the BUG ratings.
Backlight
Backlight is an important aspect of lighting design that influences the visual comfort in your environment. The BUG rating system divides backlight into subzones: backlight low (0-30 degrees), backlight mid (30-60 degrees), and backlight high (60-80 degrees) from the ground. Each subzone has a maximum lumen output, and the highest subzone rating determines the overall backlight rating. It occurs when light is emitted in the opposite direction of its intended purpose, causing unwanted brightness behind the luminaire. To control backlight, focus on selecting and positioning your luminaires wisely. Consider using fixtures with a low BUG rating for backlight to reduce the possibility of discomfort, light pollution, and trespass in your space.
Up Light
Uplight is the portion of light emitted upward from a luminaire, which can contribute to skyglow and affect both aesthetics and the environment. Uplight is divided into uplight low (UL, 90-100 degrees) and uplight high (UH, 100-180 degrees) subzones, each with its own lumen limits. The highest subzone rating determines the uplight rating. To manage uplight effectively, select fixtures with a low BUG rating. This will not only help maintain a dark sky and reduce the ecological impact but also enhance the visual appeal of your space. Utilizing fixtures with proper shielding and aiming them strategically can further minimize uplight.
BUG Ratings are a measurement of backlight (B), up light (U), and glare (G)
Glare
Glare can be a significant source of discomfort and distraction in a lit environment, as it reduces visibility and strains your eyes. Glare is assessed by measuring forward light in different subzones: forward light low (0-30°), forward light mid (30-60°), forward light high (60-80°), and forward light very high (80-90°). Forward light low and forward light mid are generally considered beneficial and are not included in glare calculations, while forward light high and very high are used to determine the glare rating. It occurs when excessive light is emitted directly into your field of view. To control glare, ensure that your luminaires have a low BUG rating for glare, and utilize appropriate shielding and optical control mechanisms. Implementing proper lighting design techniques can also assist in managing glare effectively without compromising the overall illumination of your space.
BUG Ratings Aren’t the Only Factor Used to Protect Against Light Pollution
While BUG Ratings report backlight, up light, and glare, BUG is not the only relevant factor when qualifying a light for dark sky compliance. Lumen output, Kelvin, Footcandles, and Max/Min Ratio are also important and taken into consideration.
Lumen Output
Lumen output is the total amount of light emitted by a light fixture (also referred to as lumens emitted). Excess light or unneeded light wastes energy and defeats dark sky initiatives. To limit the amount of light emitted in a given location, some communities limit the lumen output per acre.
Kelvin
Most ordinances that regulate lighting to promote dark skies and limit light pollution specify the Kelvin of the light fixture. The most frequent regulation is that the Kelvin must be 3000K or below. 2200K is preferred as it is more effective. Other objectives such as protecting wildlife, sea turtle hatchlings, or maintaining dark skies for observatories may specify narrow bandwidth of 590nm Amber.
Footcandles
Footcandles (fc) measure the amount of light on a surface. For outdoor lighting, this is usually the ground such as a walkway, driveway, or parking lot. Local regulations that protect dark skies are starting to limit the maximum footcandles on a site to 5fc.
Max/Min Ratio
A Max/Min Ratio measures the maximum number of footcandles in an area divided by the minimum number of footcandles in an area. For general egress and parking, IESNA recommends a Max/Min Ratio of 10. Now, a Max/Min ratio of 5 is starting to gain traction. A lower Max/Min ratio increases visibility while reducing hot spots or areas with an overabundance of light.
Creating a Lighting Plan
BUG ratings are an important part of planning an outdoor lighting design and will play into different elements of design, but BUG Ratings are not the only consideration. These are some of the factors involved in creating a lighting plan. When undertaking an outdoor lighting project, considering BUG ratings along with other factors ensures a well-rounded and compliant design.
Lighting Quality and Aesthetics
When planning your outdoor lighting, prioritize lighting quality and aesthetics. The illumination levels need to be adequate. The fixtures selected need to complement the architectural design of the space. Consider the color temperature of the light emitted to achieve the desired ambiance. Naturally, pay attention to the BUG Rating of the light fixtures to minimize glare and light pollution.
Light Fixture Locations
Carefully analyze your location and the area that needs illumination to determine the most effective locations for your light fixtures. Consider the following factors when deciding on luminaire positions:
- The function of the space
- Task requirements and specific areas that need focused lighting
- Ambient lighting levels
- Potential obstructions or shadows
- Mounting height
- Proximity to property lines
Moving or adjusting luminaire locations as needed can improve the overall lighting plan and avoid unnecessary costs or rework.
Understanding BUG Ratings is a first step to superior lighting
Common Mistakes to Avoid
When planning outdoor lighting, it’s easy to make mistakes that inadvertently increase light pollution. One of the most common errors is choosing light fixtures with high backlight, uplight, and glare ratings, which can result in excessive stray light and glare that disrupts both neighbors and the environment. Another frequent oversight is neglecting to consider the specific lighting zone for the area. Different zones, such as residential or commercial, have unique requirements that must be met to avoid unwanted light trespass. Failing to account for the light distribution pattern of a luminaire can also lead to light spilling beyond property lines, causing unnecessary light pollution. Over-lighting is another pitfall, as using more light than necessary not only wastes energy but also increases the impact of backlight and glare. By being mindful of these issues and utilizing the BUG rating system to guide fixture selection and placement, you can create outdoor lighting that is both effective and environmentally responsible.
Case Studies and Examples
Real-world applications of the BUG rating system demonstrate its effectiveness in reducing light pollution and improving lighting quality. For example, a city that incorporated the BUG rating system into its outdoor lighting ordinance experienced a noticeable drop in light pollution complaints from residents, thanks to the use of fixtures with low backlight, uplight, and glare ratings. In another case, a commercial outdoor lighting project for a shopping center selected luminaires with low BUG ratings, resulting in lower energy costs and positive community feedback about reduced light trespass and improved nighttime visibility. Residential areas and parking lots have also benefited from BUG-rated lighting, with property owners reporting enhanced safety and comfort without the negative effects of excessive light. Astronomical observatories, which require minimal light pollution for optimal operation, have found that implementing BUG-compliant fixtures helps preserve the darkness needed for research and stargazing. These examples highlight how the BUG rating system can be successfully applied across a range of outdoor lighting projects to achieve both functional and environmental goals.
Read the Full Case Study on the Villa Palazzo Lighting Project
Future Developments and Research
The landscape of outdoor lighting and light pollution control is rapidly evolving, with ongoing research and innovation driving improvements in the BUG rating system and lighting technology. The Illuminating Engineering Society (IES) and the International Dark Sky Association (IDA) are actively collaborating to update the Model Lighting Ordinance (MLO), ensuring that the latest scientific findings and best practices are reflected in outdoor lighting standards. Advances in LED technology and the emergence of smart lighting systems capable of adjusting light output based on time of day or ambient conditions are expected to further limit light pollution and enhance energy efficiency. There is also a growing movement to integrate the BUG rating system with broader sustainability frameworks, such as LEED certification, to promote comprehensive environmental responsibility in lighting design. As research continues and new solutions are developed, the tools available to lighting professionals and communities will become even more effective at protecting the night sky and reducing the impact of artificial light on our world.
BUG Ratings, Professional Design Services, and Photometric Studies
BUG ratings, lighting zones, max/mins, and light trespass are a lot to deal with. There are alternatives to doing it yourself.
For any outdoor lighting project, consulting with professionals ensures that all aspects, including BUG ratings, are properly addressed.
BUG Ratings and Lighting Professionals
If you are undertaking a project that requires outdoor lighting it is essential that you have a basic understanding of BUG ratings, lighting zones, Kelvin, nanometers, and other aspects of lighting. In the end, if your project needs approval from a governing body you will need to involve a lighting professional. Lighting design includes aesthetics, energy use, and compliance with local regulations and codes. That can seem rather complicated because it is.
That is why Access Fixtures has lighting specialists and lighting engineers who do lighting design. Access Fixtures lighting specialists, with the assistance of a lighting engineer, work with architects, site engineers, property managers, and other clients to determine the best initial layout that looks great, meets functional requirements and meets local ordinances and codes. Then an Access Fixtures lighting engineer runs a photometric study to model the light emitted by the proposed lighting design. If modifications are required, modifications are made, as it is much easier to change a design than change an installation.
Results are delivered in multiple pdf formats and in a dwg file. That makes permitting and approvals faster and easier. If you are working on a lighting project that will require approvals and/or permits, take the next step. To learn more about photometric studies call an Access Fixtures lighting specialist at 800.468.9925, or contact an Access Fixtures lighting specialist via the link below.
BUG Rating Frequently Asked Questions (FAQs)
You have BUG Rating questions. We have BUG Rating answers. If your question isn't answered on this page or below, click the I have a Question link below and ask an Access Fixtures lighting specialist your question.
How are BUG ratings calculated?
BUG ratings are calculated using three components: backlight (B), uplight (U), and glare (G). Each component is evaluated separately, and then these values are combined to form the overall BUG rating. This system helps you to assess the impact of a luminaire on the surrounding environment, considering factors like light pollution and visual discomfort.
Does LEED Certification take into consideration BUG ratings?
BUG ratings are used as a tool to comply with the requirements for LEED (Leadership in Energy and Environmental Design) certification, related to exterior lighting. By adhering to specific BUG rating thresholds, you can ensure that your project promotes sustainable lighting practices and minimizes light pollution, contributing positively to your LEED score.
BUG rating method meaning?
The BUG rating method is a systematic approach for evaluating the performance of outdoor lighting fixtures. By assigning values to the components of backlight, uplight, and glare, the method offers a comprehensive understanding of how a fixture potentially impacts the environment. This allows you to make informed decisions when designing or retrofitting outdoor lighting systems.
What is DarkSky’s role in BUG ratings?
DarkSky, formerly known as the International Dark-Sky Association (IDA), plays a crucial role in advocating for responsible lighting practices to minimize light pollution. DarkSky does not directly administer the BUG rating system. They make recommendations including partnering with the Illuminating Engineering Society (IES) to create a model lighting ordinance that promotes dark sky best practices. DarkSky guidelines and recommendations use BUG ratings and promote light fixtures with minimal negative effects on the environment, night sky, and human health.
What is the impact of BUG ratings on lighting?
BUG ratings impact lighting by encouraging the use of fixtures that minimize negative environmental and visual effects. By adhering to recommended BUG rating values in a lighting zone, you can design lighting systems that effectively illuminate intended areas without excessive light pollution, glare, or stray light. This results in more efficient, sustainable, and comfortable outdoor lighting.
What is the relationship between BUG and the Model Lighting Ordinance?
The Model Lighting Ordinance (MLO) is a set of guidelines developed jointly by DarkSky and the Illuminating Engineering Society (IES) to help municipalities regulate outdoor lighting. The MLO relies on BUG rating system as one of the key criteria for evaluating the appropriateness of outdoor lighting fixtures. By incorporating BUG ratings into their requirements, MLO guidelines promote responsible lighting practices that minimize light pollution in local communities.