NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 57 Notes: A growing number of organizations review and certify lighting products as “wildlife friendly” or more generally as “night sky friendly.” Examples include the IDA’s Fixture Seal of Approval program, the Florida Fish and Wildlife Conservation Commission’s Certified Wildlife Lighting program, and the DesignLights Consortium’s LUNA requirements that establish criteria for outdoor lighting at night. 5.4.5 Use Luminaires with an IES TM-15-20 BUG Rating System Uplight (U0) Rating Use luminaires with a BUG (U0) rating (formerly referred to as full-cutoff luminaires) for all permanent lighting, except as required to meet the minimum safety requirements (e.g., collision markers required by the FAA, other emergency lighting triggered by alarms). These luminaires do not emit light above the horizontal, thus substantially reducing skyglow and potentially light trespass. Additional side shielding further reduces skyglow and light trespass. BUG is an acronym for backlight, uplight, and glare. The BUG rating system replaces the “cutoff” system. The BUG rating system is a tool to quantitatively evaluate the light output of an outdoor luminaire and, in particular, light escaping in unwanted directions. The system is based on a sphere around a hypothetical pole-mounted light source in the center of the sphere (see Figure 4 in Section 5.1.2). The sphere is divided into three sections: backlight (yellow in Figure 4), uplight (blue in Figure 4), and glare (or forward light) (green in Figure 4). The three sections are further divided into zones in which the lumen distribution is rated to determine the light pollution effect of the luminaire. The BUG rating system is particularly helpful for selecting luminaires where directional lighting is a concern. For example, it is usually desirable to have very low backlight (B) ratings for lights along the edges of illuminated areas (to avoid light trespass into adjacent dark areas), while higher backlight ratings are appropriate for lights in the middle of a parking lot. Notes: Luminaires with a BUG U0 rating can still cause substantial light trespass and glare. To reduce these effects, use luminaires with low BUG ratings for backlight (B) and glare (G). Ensure the luminaire is mounted properly and not tilted, as a tilted luminaire may cast light above 90 degrees and thus no longer achieve a U0 rating. 5.4.6 Retrofit Existing Poorly Shielded Lights with Luminaires with a BUG U0 Rating It is recommended to replace existing unshielded or partially shielded luminaires with luminaires with a BUG U0 rating and low B and G (G0 preferred, G1 maximum) ratings to reduce skyglow, light trespass, and glare (Table 2). Photometrically test retrofitted lights to ensure the BUG rating of each specific luminaire type. 5.4.7 Where Necessary, Install Customized Shielding Install customized shielding where necessary so luminaires do not emit light above the contour of the land surface and cause light trespass. This is particularly important for lights installed on hilltop or sloped locations (especially on poles) that may emit light toward lower elevations, even if they have fully shielded luminaires installed horizontally. Where needed, this practice reduces light trespass and potential for glare. Additional side shielding further reduces skyglow and light trespass. Notes: Use only original equipment manufacturer-approved shields. Modifications not approved by the manufacturer may void the product warranty, cause damage to the luminaire, or present a hazard. For example, improperly installed “homemade” shields on lights may compromise the thermal mitigation of luminaires, creating a fire hazard.
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