Lighting Fundamentals – BUG Ratings

A BUG Rating stands for backlight, uplight, and glare. Backlight (B) is the light directed behind the fixture, uplight (U) is any light directed upward above the horizontal plane of the luminaire, and glare (G) is the amount of light emitted from the luminaire at high angles.

The backlight, uplight, and glare ratings are assigned a value between 0 and 5 (with lower of the scale being more desirable) depending on the maximum amount of light in these zones based on thresholds defined by the Illuminating Engineering Society (IES) and enforced by the International Dark-Sky Association (IDA).

A BUG Rating gives a simple way to quantify where the light goes in a light. In most cases, you want lower numbers as an indicator that light goes where it’s supposed to versus unintended areas. When you don’t control the light well, you get into situations where there may be consequences – such as in sensitive wildlife areas or residential neighborhoods.

So What BUG Rating Should I Look For?

The short answer is that the lower the value, the better the rating. The IES and Dark-Sky Association’s Model Lighting Ordinance has clear definitions outlined below for what recommended rating levels should be. Each area may also have their own requirements that can supersede these standards.

Below is the detailed information around BUG Ratings however the ratings in the zones defined by this system are intended to be just one of the metrics used to evaluate luminaire distribution and the potential for light pollution and obtrusive light.

Maximum Allowable BUG Ratings (Defined by the Model Lighting Ordinance)

• LZ0: No ambient lighting – Areas such as wilderness areas, parks and preserves, and undeveloped rural areas.
• LZ1: Low ambient lighting – Areas such as rural and low-density residential areas.
• LZ2: Moderate ambient lighting – Areas such as light commercial business districts and high density or mixed-use residential districts
• LZ3: Moderately high ambient lighting – Areas such as large cities’ business districts
• LZ4: High ambient lighting – Special case areas such as high-intensity business or industrial zone districts.

A detailed evaluation of the lighting should also consider the overall system design, including luminaire locations, utilization of light where it is needed, lighting quality, visual tasks, aesthetics, safety requirements, and security issues.

Our IPL series, SCL series, and SCL2 series luminaires are all intentionally designed for optimum light performance taking all aspects of good lighting design into account – one of these being keeping the BUG Rating as low as possible. All of our lights have a BUG Rating of 2 or less. In addition, all of our luminaires have an uplight rating of U0, in compliance with the International Dark-Sky Association (IDA) recommendations to reduce light pollution by only lighting the area needed.

We are here to help with any lighting project, and we can create lighting layouts and provide product recommendations that ensures your project is lit in the most efficient way keeping your BUG Rating the lowest level possible.