Auxiliary Lamps, Underglow and Light Bars

Start with what the statute lets you add. RCW 46.37.180 permits four kinds of auxiliary lamp and caps each at two. Spot lamps must be "so aimed and used that no part of the high intensity portion of the beam will strike the windshield, or any windows, mirror, or occupant of another vehicle in use." Fog lamps go on the front "at a height of not less than twelve inches nor more than thirty inches above the level surface upon which the vehicle stands," and when the vehicle is unloaded no part of the high intensity portion of the light to the left of centre may project higher than four inches below the lamp centre at twenty-five feet ahead. Auxiliary passing lamps sit between twenty-four and forty-two inches; auxiliary driving lamps between sixteen and forty-two inches. Those height bands are why a roof-mounted light bar cannot be registered as any of the four statutory lamp types on a passenger car: a roof line clears forty-two inches on almost everything.

The State Patrol rules in chapter 204-21 WAC add the performance detail. Under WAC 204-21-090 an auxiliary driving lamp must meet SAE Standard J581, must be white, and must "be wired so that the taillights are lighted whenever the driving lamps are lighted," with a separate switch and indicator lamp if it is not wired to operate only with the high beams. It may supplement the upper beam only, never replace headlamps. WAC 204-21-080 requires fog lamps to meet SAE J583, to be white to amber, and to sit with the inner edge of the lens retaining ring no closer than four inches to the optical centre of the front turn signal lamp. WAC 204-21-100 puts auxiliary passing lamps on SAE J582a, white to amber, aimed with the top edge of the high intensity zone one inch above lamp centre and the left edge five inches to the left. Spot lamps must meet SAE J591 under WAC 204-21-110. WAC 204-21-030 then governs mounting and aiming for all of it: securely on a rigid part of the vehicle to prevent noticeable vibration of the beam, at the prescribed height, aimed on a vertical screen twenty-five feet from the lens or with an optical aimer meeting SAE J600a, or set at 0-0 with a mechanical aimer meeting SAE J602c.

WAC 204-21-230 is where the prohibitions live. Subsection (1) opens with the general test, that added equipment "must not impair the effectiveness of lighting equipment required by 49 C.F.R. Part 571.108, as it exists on February 22, 2022, or chapter 46.37 RCW," then bans, for a vehicle in motion on a public roadway, aftermarket neon lighting devices, letters or symbols combined with an eye level brake light, and lighted or powered changeable sign or message boards. The exceptions are narrow: officially sanctioned traffic control vehicles, and unitized electric signs identifying taxicabs and mass transit destinations that carry no commercial or personal message. An unlit scrolling sign with no continual motion is allowed. Subsection (2) bars tinted plastic covers, grille covers or slotted covers in front of a headlamp lens, excepting clear aftermarket headlamp covers, headlamp wipers that keep the system within FMVSS 108 photometrics in any wiper position, and a bike rack on a municipal transit vehicle.

Colour is reserved by class. Red emergency lights are limited to authorized emergency vehicles, law enforcement vehicles, emergency tow trucks, school buses and private carrier buses. Blue is limited to law enforcement vehicles, fire department vehicles under RCW 46.37.184, which may run rear-facing blue lights and may combine red and blue only at the scene, and emergency tow trucks under RCW 46.37.196, which may use the combination only at the scene of an emergency or accident and never while travelling to or from it. Flashing white is limited to authorized emergency vehicles, law enforcement vehicles, school buses and emergency tow trucks. Green is limited to a firefighter's private vehicle authorized by RCW 46.37.185, a highway maintenance vehicle, and a snow removal vehicle owned or operated by a state, county or municipal agency. RCW 46.37.185 requires the firefighter's green light to be visible for two hundred feet, to be of a type and mounting approved by the State Patrol, and to confer none of the emergency-vehicle privileges in RCW 46.61.035.

Three statutory backstops apply to any lamp you add. RCW 46.37.280(1) requires that any lighted lamp other than head lamps, spot lamps, auxiliary lamps, flashing turn signals and authorized warning lamps that projects more than three hundred candlepower be aimed so no part of the high intensity portion of the beam strikes the roadway more than seventy-five feet from the vehicle. RCW 46.37.280(2) forbids driving with any lamp displaying a red light visible from directly in front of its centre. RCW 46.37.280(3) prohibits flashing lights altogether except as required by the emergency and warning sections, warning lamps authorized by the State Patrol, and light-emitting diode flashing taillights on bicycles.

The parked carve-out is the practical answer for show cars. WAC 204-21-230(1)(b) provides that "If a vehicle is not in motion and parked on private property, the vehicle may use aftermarket lighting except as outlined under RCW 46.37.180." Underglow is therefore legal to install and legal to run at a meet or in a driveway, and unlawful the moment the car moves on a public roadway.

010(1)(b) reaches a vehicle not equipped with lamps in proper working condition and adjustment as required by the chapter or those rules. 110(8)(a) unless the court finds the driver indigent. 060 makes it unlawful to operate a vehicle whose equipment is not in proper condition as required by the title or by rules adopted by the chief of the State Patrol, and empowers any peace officer to impound an unsafe vehicle until the defect is corrected, with impound and storage costs paid by the owner.

010(1) limiting inspection stations to commercial motor vehicles, school buses and private carrier buses, an illegal light bar or underglow kit is found only at the roadside. Displaying red or blue emergency lighting reserved to police and fire vehicles also risks charges beyond the equipment chapter for impersonating an officer.