Cal. Code Regs. tit. 13 § 685
Lighting equipment shall be securely mounted on a rigid part of the vehicle to prevent noticeable vibration of the beam and shall be maintained with the proper aim when the vehicle is stationary and in motion. No lighting device, unless otherwise permitted, shall be mounted so any portion of the vehicle, load, or vehicle equipment interferes with the distribution of light or decreases its intensity within the photometric test angles unless an additional device is installed so the combination of the two meets these requirements. Mounting heights shall be measured from the center of the lamp or reflector to the level surface upon which the vehicle stands when it is without load.
Cal. Code Regs. Tit. 13, § 685
Note: Authority cited: Section 26103, Vehicle Code. Reference: Sections 24012 and 26103, Vehicle Code.