BUG ratings are one of the multiple ways in which lighting product performance is measured and quantified to serve specific technical purposes. BUG is an acronym for backlight (B), uplight (U) and glare (G). Light directed behind the fixture is considered to be backlight, whereas light directed up above the horizontal plane of the fixture is considered to be uplight. Glare measures the amount of light emitted from the luminaire at high angles to the sides. Essentially, BUG ratings are a straightforward way to quantify where the light in a light fixture actually goes.
These measurements are given a specific value between 0 and 5 depending on the maximum amount of light measured in each zone. Lower numbers in these areas are considered desirable, because it means the light is going where it is supposed to be, which is particularly important for sensitive areas such as residential neighborhoods. These values are measured using the thresholds defined by IES, or Illuminating Engineering Society. They are enforced by the IDA, or International Dark-Sky Association.
Ideal BUG Ratings
Ideally, all BUG ratings should be as close to zero as possible. Both IDA and IES outline recommended rating levels based on different zone or area requirements. These are general guidelines that may be superseded by individual area requirements depending on the situation. Listed below are the different zones as defined by the Model Lighting Ordinance.
- LZ0: No ambient lighting – This includes areas of undeveloped open land such as wilderness reserves, nature parks, areas near observatories or areas where protection and preservation of a dark environment is important.
- LZ1: Low ambient lighting – Includes areas such as rural and residential zoned single family homes. Also includes rural town centers, commercial districts and corporate business parks with limited after hours nighttime activity.
- LZ2: Moderate ambient lighting – Most common zone, which includes areas with moderate ambient lighting levels such as light commercial business districts, multi-family or mixed-use residential zones, hotels and neighborhood business districts, churches, hospitals, schools, etc.
- LZ3: Moderately high ambient lighting – Areas such as large cities’ business districts and commercial corridors such as car dealers, shopping malls, gas stations and town centers. Also includes mixed used industrial zones such as docks, rail yards and shipping centers with high nighttime activity.
- LZ4: High ambient lighting – Unusual situations with high intensity business or industrial zones. Also includes special cases such as high density entertainment districts and downtown areas.
It should be noted that overall system design should be considered when reviewing the detailed evaluation of lighting fixtures. This includes the location of luminates, as well as the utilization of light where it is needed, with lighting quality, aesthetics, security and safety issues taken into account.
Other Factors Affecting Lighting Pollution
In addition to BUG ratings, there are several other factors that affect lighting pollution:
Lumen Output: This is the measurement of the total light emitted by a fixture. Excessive light wastes energy and disrupts dark sky initiatives. Some communities limit lumen output per acre to reduce light pollution.
Kelvin Ratings: This indicates the color temperature of light. Regulations often cap this at 3000K, with 2200K preferred for greater effectiveness. Specific scenarios, such as protecting wildlife or preserving observatory skies, may require narrow-band amber light at 590nm.
Footcandles (fc): FC is a measurement of the light intensity on surfaces like walkways or parking lots. Many dark sky ordinances now limit outdoor lighting to a maximum of 5fc to curb unnecessary brightness.
Max/Min Ratios: This compares the brightest and dimmest points in a lit area. While a ratio of 10 is standard, a ratio of 5 is gaining popularity for enhancing visibility and reducing hotspots.