Head lamp.
Automotive headlights are generally composed of three parts: light bulb, reflector and matching mirror (astigmatism mirror).
1. bulb
The bulbs used in automobile headlights are incandescent bulbs, halogen tungsten bulbs, new high-brightness arc lamps and so on.
(1) Incandescent bulb: its filament is made of tungsten wire (tungsten has a high melting point and strong light). During manufacturing, in order to increase the service life of the bulb, the bulb is filled with an inert gas (nitrogen and its mixture of inert gases). This can reduce the evaporation of tungsten wire, increase the temperature of the filament, and enhance the luminous efficiency. The light from an incandescent bulb has a yellowish tinge.
(2) Tungsten halide lamp: Tungsten halide light bulb is inserted into the inert gas into a certain halide element (such as iodine, chlorine, fluorine, bromine, etc.), using the principle of tungsten halide recycling reaction, that is, the gaseous tungsten evaporating from the filament reacts with the halogen to produce a volatile tungsten halide, which diffuses to the high temperature area near the filament, and is decomposed by heat, so that the tungsten is returned to the filament. The released halogen continues to diffuse and participate in the next cycle reaction, so the cycle continues, thereby preventing the evaporation of tungsten and the blackening of the bulb. Tungsten halogen light bulb size is small, the bulb shell is made of quartz glass with high temperature resistance and high mechanical strength, under the same power, the brightness of tungsten halogen lamp is 1.5 times that of incandescent lamp, and the life is 2 to 3 times longer.
(3) New high-brightness arc lamp: This lamp has no traditional filament in the bulb. Instead, two electrodes are placed inside a quartz tube. The tube is filled with xenon and trace metals (or metal halides), and when there is enough arc voltage on the electrode (5000 ~ 12000V), the gas begins to ionize and conduct electricity. The gas atoms are in an excited state and begin to emit light due to the energy level transition of the electrons. After 0.1s, a small amount of mercury vapor is evaporated between the electrodes, and the power supply is immediately transferred to the mercury vapor arc discharge, and then transferred to the halide arc lamp after the temperature rises. After the light reaches the normal working temperature of the bulb, the power of maintaining the arc discharge is very low (about 35w), so 40% of the electric energy can be saved.
2. reflector
The role of the reflector is to maximize the polymerization of light emitted by the bulb into a strong beam to increase the irradiation distance.
The surface shape of the mirror is a rotating paraboloid, generally made of 0.6 ~ 0.8mm thin steel sheet stamping or made of glass, plastic. The inner surface is plated with silver, aluminum or chrome and then polished; The filament is located at the focal point of the mirror, and most of its light rays are reflected and shot out into the distance as parallel beams. The light bulb without a mirror can only illuminate a distance of about 6m, and the parallel beam reflected by the mirror can illuminate a distance of more than 100m. After the mirror, there is a small amount of scattered light, of which the upward is completely useless, and the lateral and lower light helps to illuminate the road surface and curb of 5 to 10m.
3. lens
Pantoscope, also known as astigmatic glass, is a combination of several special prisms and lenses, and the shape is generally circular and rectangular. The function of the matching mirror is to refract the parallel beam reflected by the mirror, so that the road in front of the car has a good and uniform lighting.
sort
The headlamp optical system is a combination of light bulb, reflector and matching mirror. According to the different structure of the headlamp optical system, the headlamp can be divided into three kinds: semi-closed, closed and projective.
1. Semi-enclosed headlight
Semi-closed headlamp lighting mirror and mirror stick together can not be disassembled, light bulb can be loaded from the rear end of the mirror, semi-closed headlamp advantage is that the filament burned only need to replace the bulb, the disadvantage is poor sealing. The combined headlamp combines the front turn signal, the front width light, the high beam light and the low light into a whole, while the reflector and the pantoscope are made into a whole using organic materials, and the bulb can be easily loaded from the back. With combined headlights, automotive manufacturers can produce any type of headlight matching lens on demand in order to improve vehicle aerodynamic characteristics, fuel economy and vehicle styling.
2. Enclosed headlights
Enclosed headlamps are also divided into standard enclosed headlamps and halogen enclosed headlamps.
The optical system of the standard enclosed headlamp is to fuse and weld the reflector and the matching mirror into a whole to form the bulb housing, and the filament is welded to the reflector base. The reflector surface is aluminized by vacuum, and the lamp is filled with inert gas and halogen. The advantages of this structure are good sealing performance, the mirror will not be polluted by the atmosphere, high reflection efficiency, and long service life. However, after the filament is burned out, the entire lighting group needs to be replaced, and the cost is higher.
3. Projective headlamp
The optical system of projective headlamp is mainly composed of light bulb, reflector, shading mirror and convex matching mirror. Use a very thick non-engraved convex mirror, the mirror is oval. So its outside diameter is very small. Projective headlights have two focal points, the first focus is the bulb and the second focus is formed in the light. Focus the light through the convex mirror and cast it into the distance. Its advantage is that the focus performance is good, and its ray projection path is:
(1) The light emitted to the upper part of the bulb passes through the reflector to the second focus, and is focused to the distance through the convex matching mirror.
(2) At the same time, the light emitted to the lower part of the bulb is reflected by the masking mirror, reflected back to the reflector and then thrown to the second focus, and focused to the distance through the convex matching mirror.
In the use of cars, the requirements for headlights are: both to have good lighting, but also to avoid blinding the driver of the oncoming car, so the use of headlights should pay attention to the following points:
(1) Keep the headlamp pantoscope clean, especially when driving in rain and snow, dirt and dirt will reduce the lighting performance of the headlamp by 50%. Some models are equipped with headlight wipers and water sprays.
(2) When the two cars meet at night, the two cars should turn off the high beam of the headlamp and change to the near light to ensure driving safety.
(3) In order to ensure the performance of the headlamp, the headlamp beam should be checked and adjusted after the headlamp is replaced or after the car is driven 10,000 km.
(4) Regularly check the light bulb and line socket and the base iron for oxidation and loosening, to ensure that the connector contact performance is good and the base iron is reliable. If the contact is loose, when the headlamp is switched on, it will produce a current shock due to the on-off of the circuit, thus burning the filament, and if the contact is oxidized, it will reduce the brightness of the lamp due to the increase of the contact pressure drop.
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