Industry News

The Changing role of LED in automotive Lighting application (1)

Published by admin October 12,2021


1. Introduction

Most roads in North America and the rest of the world are not illuminated by road lighting systems mounted on masts, so car lighting is a key component of safe driving at night.

Performance requirements for automotive headlights are based on standards and recommendations issued by the Institute of Automotive Engineers (SAE) and similar industry organizations.
These requirements specify the minimum or maximum intensity of illumination from the centre of the vehicle lighting system in different directions.

Similar photometric requirements exist outside North America;
These regulations may vary in detail, but they all specify the intensity of light to ensure that the vehicle lighting system provides sufficient light for drivers to see the road, minimizes glare to other drivers, and ensures that vehicle signals can be detected in a timely and clear manner.

2. The headlights

For car headlights that illuminate the front of the vehicle, two should be installed as far away as possible.
Each headlight must meet the same performance requirements.
There are two main types of beam patterns: high beam and low beam.
Table 1 and Table 2 show the north American requirements for several angular positions for high and low beam headlights.

Table 1: Some luminosity requirements for high beam high beams in the United States

Table 2: Some luminosity requirements for low beam high beams in the United States

As expected, high beams require a higher intensity and a smaller maximum intensity value.
In addition, the far beam has a symmetrical beam pattern.
In contrast, the near beam has an asymmetric beam pattern, with a more rigid maximum tilting to the left (in North America;
If the country is on the left, the beam pattern is reversed from left to right.

Figure 1 shows the intensity requirements of the low-beam headlight pattern, which is superimposed on the corner of a straight two-lane road.
By using the inverse square law, the Angle luminance intensity can be converted into the illumination on the road and the object in front of the vehicle.
The illuminance of each headlight should be added together to obtain the total.

Figure 1: Luminosity requirement for us low-beam headlight pattern, superimposed on a two-lane image.

Figure 2 shows a low-beam headlight pattern projected onto the wall in front of the headlight.
To reduce glare to the driver in front of you, the low-beam mode will usually have a vertical gradient as shown in Figure 20.2.
Above the so-called cutoff boundary between the light and dark parts of Figure 20.2, the intensity is low and the light is insufficient.

Figure 2: A low beam headlight pattern projected onto a wall.

Cutoff boundaries can be checked and adjusted for the vertical target of the headlight.
Most North American headlights require the right cut-off to be at the same height as the headlight.
The left cut-off is usually lower than the right to reduce the amount of light entering the oncoming driver's eye.
The "harsh" cutoff boundary of the low-beam headlight pattern limits the visibility of the driver ahead.

When driving at speeds exceeding 60-65 km/h, drivers using low-beam headlights may find it difficult to detect potential hazards in time and stop.
In this case, the high light speed is guaranteed unless the approaching vehicle is within 100 meters.
However, most drivers underuse their high-light headlights.

Because the cutoff boundary of the low-beam headlight pattern is clear, the vertical target is an important factor in achieving optimal performance.
In the US, for example, most states do not require headlights as part of safety checks.
A recent study of vehicle vertical targets found that most vehicles have at least one poorly targeted headlight.
When the target is too high, headlights may cause an uncomfortable glare.
When the target is too low, the visibility ahead of the driver will be affected.

Adaptive lighting system is based on the speed, the direction of the Angle to automatically adjust the nearlight Angle side, expand the effective lighting range when the vehicle turning.
Automatic horizontal adjustment ensures that no matter how heavy the load is, the light is always directed to the ground ahead.
Some vehicles have turn and bend lights;
Bent lamps sometimes use mechanical elements to Orient one or both headlights toward the curve of the road.

Some European vehicles are equipped with a "town" headlight beam pattern, which has a lower maximum luminous intensity and is more widely distributed than most low-beam models, helping drivers detect pedestrians at low urban speeds.
Adaptive lighting requirements in most countries are based on the United Nations Economic Commission for Europe (ECE) Vehicle Code no. 123.
America's Federal Motor Vehicle Safety Standard 108 currently has reservations about adaptive lighting.

At present, most automotive headlamps use a filament source (tungsten halogens or simpler halogens) from a mirror or projector optical system to produce the necessary beam pattern.
A relatively small proportion of headlights use high intensity discharge (HID) lamps, and metal halides and xenon lamps to switch on quickly.
LED headlights are just beginning to be used on several models.
All headlamps need to meet the same luminosity requirement regardless of the light source used.

3. The light

Cars need to have lights so that drivers can alert others when braking and turning between day and night.
Nowadays, more and more vehicles use LEDS for signal lighting.
Different lights have different requirements for color and light intensity.
Federal requirements for vehicle signals in the United States are based on SAE standards and recommendations.
Table 3 lists the colors and allowed luminance intensity values for several vehicle semaphore types.

Table 3: Luminosity and color requirements for traffic lights in the U.S.

The performance requirements for car lights in Europe are not much different from those in North America in terms of color and intensity of light, with one exception.
In the United States, traffic lights on the back of vehicles can be red or yellow, with different intensity requirements, depending on their color.
In most other parts of the world, the backturn signal must be yellow.

Allen previously reported that yellow backturns tend to have fewer collisions, either because they emit more light than red backturns, or because yellow makes them easier to distinguish between brake lights and taillights.
The National Highway Traffic Safety Administration (NHTSA) is considering whether it needs to turn the steering signal yellow for all rear-end vehicles.