Bonneville County, ID Outdoor Lighting: Billboard Lighting (2026)

Section 152.30(D)(4)-(5) sets the nighttime brightness ceiling for LED and tri-vision billboard faces in unincorporated Bonneville County. Before the county issues a sign permit, the applicant must document that the billboard is equipped with a photocell dimmer that automatically reduces brightness as ambient light falls, and that dimmer must run at all times the sign operates.

The illumination limit is measured against the sign's own baseline: an inspector uses an illuminance meter accurate to two decimal places, first reading the sign turned off and then reading it displaying a solid white image, or a solid message on a single-color sign. The difference between those two foot-candle readings cannot exceed 0.3 foot-candles, and the reading must be taken one-half hour after sunset, perpendicular to the sign face, at a measurement distance keyed to the sign's square footage. The code's table sets that distance at 141 feet for a 200-square-foot billboard, rising to 259 feet for a 672-square-foot sign, with a formula (distance = sign area x 100) for any size not listed. This is the same 0.3 foot-candle standard, photocell mandate, and distance table that § 152.26 applies to on-premises electronic message center signs, so off-premises billboards and on-site electronic signs are held to an identical brightness ceiling. The Planning and Zoning Director reviews the pre-permit dimmer certification and can require the dimmer be protected from end-user tampering by password-protected software.