New Jersey Statutes Title 39. Motor Vehicles and Traffic Regulation 39 § 3-54.10

No more than two emergency warning lights shall be installed on a vehicle. If one light is used it shall be installed in the center of the roof of the car, or on the front of the vehicle so that the top of the emergency warning light is no higher than the top of the vehicle's headlights, or in the center of the dashboard. It may be a low profile light bar of the strobe, halogen or incandescent type, or a combination thereof. If two lights are used they may be placed on the windshield columns on each side of the vehicle where spotlights are normally mounted, or on either side of the roof at the front of the vehicle directly back of the top of the windshield. Under no circumstances may one light be placed on the roof and one on the windshield column in the spotlight position.Light elements shall be shielded from direct sight or view of the driver.