1 Introduction
Most roads in North America and the rest of the world are not illuminated by road lighting systems that are fixedly mounted on masts, so car lighting is a key component of safe driving at night.
The performance requirements for automotive headlamps are based on standards and recommendations issued by the Society of Automotive Engineers (SAE) and similar industry organizations. These requirements specify the minimum or maximum luminous intensity that is illuminated from the center of the vehicle's lighting system in different directions.
Similar photometric performance requirements exist in countries outside North America; these regulations may vary in detail, but specify the luminous intensity to ensure that the vehicle lighting system provides sufficient light for the driver to look at the road, minimizing The glare of other drivers ensures that the vehicle lights can be detected in a timely and clear manner.
2. Headlights
For car headlights that provide illumination for the front of the vehicle, two are required and need to be installed as far as possible. Each headlamp must meet the same performance requirements. There are two main types of beam patterns: high beam and low beam. Tables 1 and 2 give the requirements for several angular positions of high and low beam headlamps in North America.
Table 1: Some photometric requirements for high beam high beam lamps in the United States
Table 2: Some photometric requirements for low beam high beam lamps in the United States
As expected, the requirement for high beam is higher intensity and smaller maximum intensity values. In addition, the high beam has a symmetrical beam pattern. In contrast, the low beam has an asymmetrical beam pattern, and the more stringent maximum tends to the left (in North America; if it is the left-hand country, the beam pattern is reversed from left to right).
Figure 1 shows the intensity requirements for a low beam headlamp pattern, with the headlamps superimposed on the angular position of a straight two-lane road. Using the inverse square law, the angular luminous intensity value can be converted into illumination on the road and on the object in front of the vehicle; the illumination of each headlamp should be added together to obtain the total.
Figure 1: The luminosity requirements of the US low beam headlight pattern are superimposed on a two-lane image.
Figure 2 is a photograph of a low beam headlamp pattern projected onto the wall in front of the headlights. In order to reduce the glare that is given to the driver in front, the low beam mode usually has a vertical gradient as shown in Figure 20.2. Above the so-called cut-off boundary between the light and dark portions of Figure 20.2, the intensity is low and the light is insufficient.
Figure 2: Photograph of a low beam headlamp pattern projected onto a wall.
The cutoff boundary allows you to check and adjust the vertical target of the headlamps. Most North American headlights require the right cutoff boundary to be at the same height as the headlamps. The left cutoff boundary is usually lower than the right border to reduce the amount of light entering the oncoming driver's eyes. The "glare" cut-off boundary of the low beam headlight pattern limits the front visibility of the driver.
When driving at speeds in excess of 60-65 km/h, it may be difficult for the driver to use low beam headlamps to detect potential hazards in time and stop. In this case, the speed of light is guaranteed unless the nearby vehicle is within 100 meters. However, most drivers do not make full use of high beam headlights.
Since the cutoff boundary of the low beam headlamp pattern is clear, the vertical target is an important factor in achieving optimum performance. For example, in the United States, most states do not require headlamps as part of a security check. A recent study of vertical targets on vehicles found that most vehicles had at least one headlamp with poor targets. When the target is too high, the headlights may cause uncomfortable glare. When the target is too low, the visibility of the driver's front will be affected.
The adaptive lighting system automatically adjusts the steering angle side of the low beam according to the speed of the vehicle and the direction of the direction of the direction, and expands the effective illumination range when the vehicle turns. The automatic leveling function ensures that the light always shines in front of the ground, regardless of the load condition. Some vehicles have turning and cornering lights; curved lights sometimes use mechanical components to orient one or two headlamps toward the road.
Some European vehicles are equipped with a "town" headlamp beam pattern that has a lower maximum luminous intensity and a wider distribution than most low beams, helping drivers to detect pedestrians while driving at low speeds in the city. Adaptive lighting system requirements in most countries are based on the United Nations Economic Commission for Europe (ECE) No. 123 vehicle regulations. The US Federal Motor Vehicle Safety Standard 108 currently has reservations about adaptive lighting systems.
Currently, most automotive headlamps use a filament source (tungsten halogen or simpler halogen) of the mirror or projector optics to produce the necessary beam pattern. A relatively small proportion of headlamps use high intensity discharge (HID) lamps, using metal halides and xenon lamps to quickly turn the lights on. The use of LED headlights has just begun to be used on several models. Regardless of the source used, all headlamps need to meet the same luminosity requirements.
3. Signal light
Vehicles need to have a signal light so that the driver can alert others during braking and steering during the day and night. Nowadays, more and more vehicles use LEDs for signal illumination. Different signal lights have different requirements for color and luminous intensity. The US federal requirements for vehicle signals are based on SAE standards and recommendations. Table 3 lists the color and allowable luminous intensity values ​​for several vehicle signal types.
Table 3: Photometric and color requirements for US automotive signal lights
The performance requirements of European car lights are not much different from those in North America in terms of color and luminous intensity, with one exception. In the United States, the lights on the back of the vehicle may be red or yellow, with different strength requirements depending on their color. In most other parts of the world, the turn signal must be yellow.
Allen previously reported that the yellow rear turn signals tend to have fewer collisions, either because their luminous intensity is higher than the red rear turn signal, or because yellow makes it easier to distinguish between the brake light or the tail light. The National Highway Traffic Safety Administration (NHTSA) is considering whether it needs to turn yellow for all rear-mounted car steering signals. (Compile: LEDinside James)
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