How to Test Your Car’s Headlamps
A car’s headlamps should illuminate the road to help you see, but if they’re too bright they can blind other drivers with excessive glare. A good way to test yours is to have someone stand behind the vehicle, roll down the window and rotate the headlight control dial to each position, pausing between each to determine the setting.
Indicator lights
Usually, two lights indicate which headlamps are on and which ones are dimmed (for other road users). A blue light with a slash through it means the high beams are on (be sure to dim these for oncoming traffic). A green light with an arrow pointed downward indicates the fog lights are on. The indicator lights are activated automatically at dusk.
When the headlamps are switched on, they produce only a limited amount of usable light. This is to avoid blinding other road headlamp car users, especially when the vehicle is traveling in a city.
In order to produce sufficient light, the tungsten filament in headlamp bulbs and sealed beams must burn for a long time. This results in a layer of blackening on the bulb glass, which cuts down on the amount of light that is emitted. Sealed beam units and some headlamps with replaceable bulbs use a special coating to reduce this effect.
For some vehicles, the headlamps are mechanically connected to the steering mechanism so that they follow the front wheels as the car corners. This feature was first used on the Czechoslovak Tatra in 1930 and the American 1948 Tucker Sedan, but is also found on later models such as the French 1967 Citroen DS.
Most European cars have a switch to allow the headlamps to be adjusted for right- or left-hand traffic, where the light distribution differs between the two standards. The switches are normally situated in the dash near the steering wheel.
Sidelights
Depending on the manufacturer, the sidelights may be located on a control arm near the base of the steering wheel or in the headlamp unit itself. On most cars, the controls will be marked with standard headlight indicator symbols that look like a sun or upside-down light bulb. Look for an enclosed circle next to the symbol that marks the side of the dial actually controlling the headlight settings; align it with the setting you wish to activate.
The first electric headlamps used plain tungsten filament bulbs operating in an evacuated or inert-gas atmosphere. They produced small amounts of light compared to the power they consumed and often blackened over time. This reduced their efficiency, since the darkened glass blocks much of the light that would pass through an unblackened bulb.
Most modern vehicles use halogen lamps, which consume less electricity and produce a more focused beam. These are available in a variety of shapes and sizes, including Xenon H1 (55 watts @ 12.0 V, 1550 lumens +-15%), the type most commonly used in European cars.
Newer headlamp systems, such as Adaptive Highbeam Assist in Mercedes-Benz vehicles, can automatically tailor the headlight range to ensure that the beam reaches other vehicles without blinding them. Such systems can also react to road conditions, such as vehicle speed, weather and visibility, road curvature and contour, and terrain elevation.
High beams
A high beam setting on your headlamps throws brighter light rays at the distance on the road. Using this feature in certain conditions can allow you to see farther down the road at night, but it also reduces the visibility of oncoming traffic. It is important to know when and how to use this setting, not only for your own safety but also the safety of other drivers on the road.
When you activate the high beams on your car, the powerful blast of light can blind other drivers and cause them to lose sight of the road for a few seconds. This is particularly dangerous if you are driving on rural roads or highways in the dark and there are no other vehicles nearby. It is important to dim your headlamps when another vehicle approaches you from behind.
Many cars come with two headlight bulbs, a low-beam and a high-beam setting. Some older tungsten headlamps, such as those in some Jaguar and Ford products from the headlamp car late 1960s through the early 1980s, had one filament that could be shifted between low and high by changing the position of the bulb holder.
Modern headlight systems often use LED bulbs for both the low- and high-beam settings. These consume less energy and emit a much brighter light than traditional halogen bulbs. In some cases, the system may be able to automatically switch between the two settings depending on weather or road conditions.
Low beams
A vehicle’s low beam, also known as a dipped headlamp, gives enough light to see the road ahead of you but not so much that it dazzles other drivers. It’s important to use this setting in heavy traffic situations at night, when it is raining, and when the road is covered with snow or ice.
Most modern cars have a single bulb that is used for both the low and high beams. These bulbs are usually halogen, but HID bulbs are becoming more common as well. In older cars, the two different beams are created by separate bulbs. If one burns out, you need to replace the whole bulb rather than just the high or low beam section of the light.
The low beam setting is usually indicated by a light with a “dipped” symbol on it. You can dip your headlights manually using a switch inside the car, or your vehicle may be equipped with automatic dipping when it senses that conditions require you to do so. Some automakers are now using sensors that adjust your headlight settings automatically, depending on vehicle speed and road curvature and contour. This system is sometimes called adaptive front lighting or AFS. Its purpose is to provide the most useful and safe headlight setting in any given driving situation as traffic, weather, and road conditions change.