CA Veh Code § 25108 (2021)
2021 California Code|Vehicle Code - VEH|DIVISION 12 - EQUIPMENT OF VEHICLES|CHAPTER 2 - Lighting Equipment|ARTICLE 6 - Side and Fender Lighting Equipment|Section 25108.

25108.  (a) Any motor vehicle may be equipped with not more than two amber turn-signal pilot indicators mounted on the exterior. The light output from any indicator shall not exceed five candlepower unless a provision is made for operating the indicator at reduced intensity during darkness in which event the light output shall not exceed five candlepower during darkness or 15 candlepower at any other time. The center of the beam shall be projected toward the driver.(b) Any vehicle may be equipped with pilot indicators visible from the front to monitor the functioning or condition of parts essential to the operation of the vehicle or of equipment attached to the vehicle that is necessary for protection of the cargo or load. The pilot indicators shall be steady-burning, having a projected lighted lens area of not more than three-quarters of a square inch and have a light output of not more than five candlepower. The pilot indicator may be of any color except red.(c) Other exterior pilot indicators of any color may be used for monitoring exterior lighting devices, provided that the area of each indicator is less than 0.20 square inches, the intensity of each indicator does not exceed 0.10 candlepower, and the color red is not visible to the front.(d) Any towed vehicle may be equipped with an exterior-mounted indicator lamp used only to indicate the functional status of an antilock braking system providing that either of the following conditions are met:(1) The indicator lamp complies with the applicable requirements of the federal motor vehicle safety standards.(2) The indicator lamp is designed and located so that it will be readily visible, with the assistance of a rearview mirror if necessary, to the driver of the towing motor vehicle and the indicator lamp has a light source not exceeding five candlepower. The light shall not show to the sides or rear of the vehicle and the indicator lamp may emit any color except red.(e) (1) Notwithstanding any other provision of law, any motor vehicle may be equipped with not more than two exterior-lighted data monitors that transmit information to the driver of the vehicle regarding the efficient or safe operation, or both the efficient and safe operation, of the vehicle.(2) Data monitors shall comply with all of the following conditions:(A) Be mounted to the vehicle in a manner so that they are readily visible to the driver of the vehicle when the driver is seated in the normal driving position. Data monitors shall not be designed to convey information to any person other than the driver of the vehicle.(B) Be limited in size to not more than two square inches of lighted area each.(C) Not emit a light brighter than reasonably necessary to convey the intended information.(D) Not project a glaring light to the driver or, to other motorists, or to any other person.(3) Data monitors may incorporate flashing or changing elements only as necessary to convey the intended information. Data monitors shall not resemble any official traffic-control device or required lighting device or be combined with any required lighting device.(4) Data monitors may display any color, except that the color red shall not be visible to the front of the vehicle.(Amended by Stats. 2001, Ch. 739, Sec. 21. Effective January 1, 2002.)