February 24, 2006
LIMITATIONS ON HEADLIGHT BRIGHTNESS
By: James J. Fazzalaro, Principal Analyst
You asked if Connecticut law establishes maximum or minimum requirements for the brightness of motor vehicle headlights. You also asked if this is regulated by federal law.
Connecticut law establishes several requirements for the performance of motor vehicle headlamps, but the maximum light output of motor vehicle headlamps is set by federal not state regulation.
STATE REQUIREMENTS FOR HEADLAMPS
Connecticut laws regarding motor vehicle headlamps specify the following:
1. Every motor vehicle, except motorcycles, must have at least two head lamps with at least one on each side of the vehicle's front. Headlamps must be mounted at a height of not less than 22 inches or more than 54 inches. Motorcycles must have at least one, but not more than two head lamps. (CGS § 14-96b)
2. Every motor vehicle, except motorcycles, must be equipped with one or more lamps which, when lighted, shall display a white or amber light visible from a distance of 1,000 feet to the front of the vehicle, and a red light visible from a distance of 1,000 feet to the rear of the vehicle. Any lighted headlamps on a parked vehicle must be depressed or dimmed. (CGS § 14-96l)
3. Any light visible from the front of a motor vehicle may be only white, yellow, or amber in color unless another color is allowed under a Department of Motor Vehicles permit. (CGS § 14-96p)
4. The headlamps, auxiliary lamps, or combinations of both of these, on any motor vehicle other than a motorcycle must be arranged so that the driver may control the selection between distributions of light projected to different elevations subject to specific limitations set forth in the law. There must be an uppermost distribution of light, or composite beam, aimed and of such intensity to show people and vehicles at a distance of at least 500 feet for all conditions. There must be a lowermost distribution of light aimed and of sufficient intensity to show people and vehicles at a distance of at least 100 feet ahead and, on a straight level road, none of the high intensity portion of the beam can be directed to strike the eyes of an approaching driver. (CGS § 14-96t)
5. Whenever a motor vehicle is being operated on a road or road shoulder during the times headlights are required, the driver must use a light distribution, or composite beam, directed high enough and of sufficient intensity to show people and vehicles at a safe distance ahead, but (1) when approaching an oncoming vehicle within 500 feet, the driver must adjust the lights so that glaring rays are not projected into the eyes of the oncoming driver and (2) when approaching within 300 feet of another vehicle from behind, the driver must use a distribution of light other than the uppermost distribution (i.e., low beam rather than high beam). (CGS § 14-96u)
6. Whenever a motor vehicle with head lamps is also equipped with auxiliary lamps, a spot light, or any other types of lamps on the front that project a beam of intensity greater than 300 candle power, no more than a total of four such lamps may be lighted at one time. (CGS § 14-96y)
FEDERAL REQUIREMENTS FOR MOTOR VEHICLE LIGHTING
All lighting on motor vehicles is governed by Federal Motor Vehicle Safety Standard (FMVSS) No. 108. This is a federal regulation promulgated by the National Highway Traffic Safety Administration under its general authority to regulate motor vehicle equipment granted by the federal Motor Vehicle Safety Act. The federal lighting standards apply to the original equipment on motor vehicles and to replacements for this original equipment. The entities subject to the requirements include manufacturers, importers, distributors, dealers, and motor vehicle repair businesses. Lights and lighting equipment must be marked with certain designations that show its compliance with the federal standards. (49 CFR § 571.108)
The standards do not set a single maximum intensity for all possible types and designs or headlamps because the types of lights and lighting systems designed by manufacturers make a single standard impossible. Rather, FMVSS No. 108 determines the maximum allowable light intensity for a light by its design and the type of lighting system being used. The maximum light output for a particular headlight is determined at a specific point in its aiming pattern. Other maximums apply at other points in the light's aiming pattern. Compliance is determined through a specific set of test procedures.
The federal lighting standard is very complex and is difficult to interpret even for some manufacturers and lighting specialists. The actual performance standards are based principally on the standards developed by the Society of Automotive Engineers (SAE). FMVSS No. 108 and the SAE standards apply to all vehicles registered in the United States, regardless of the headlamp filament or light source. Stated simply, the maximum light output of headlamp systems, whether two-or four-light systems, is limited as follows:
1. Type 2 or 2A Lights—Upper beam limited to 20,000 to 75,000 candela per lamp. Lower beam limited to 15,000 to 20,000 candela per lamp.
2. Type 1 or 1A Lights—Upper beam limited to 18,000 to 60,000 candela per lamp.
A candela is the basic unit of measure of luminous intensity in the International System of Units. Although the candela has a specific technical definition expressed in terms of a specific frequency and power, in layman's terms it approximates the light output of a common candle. A 100-watt light bulb emits about 120 candela.