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Lights and Accessories

How car headlights work and how to care for them

Inspecting wiper blades, headlights, indicators and brake lights can help improve driving visibility.


The earliest headlamps were fuelled by acetylene or oil and were introduced in the late 1880s. Today, headlights come with bright and dim settings. This allows drivers to use brights when no other cars are in view, and dim for city driving.

The headlights are powered by the vehicle’s internal 12-volt electrical system that also powers other electrical accessories such as the radio, windshield wipers and brake lights. There are primarily two types of headlights. The conventional sealed beam type which produces about 150 000 candlepower and the halogen capsule which produces a 25 percent higher output of whiter light for the same amount of power.

How headlights work

Some headlights work differently to others, but all are actuated when the filament inside the casing receives electrical power. Some headlights use inert gases, which glow brightly when electricity is applied, and others use a wire-type filament that gets hot and glows brightly. High-intensity discharge (HID) lights use a Xenon gas that glows brightly when current is applied. Halogen uses a mixture of gas combined with a hot wire element. Incandescent bulbs use only hot wire elements to illuminate the road.

How to Care for your Headlights

Headlights require periodic maintenance. Because sealed beam headlights are modular, when the filament burns out, the entire sealed beam unit is replaced. The headlight focus must be properly checked and adjusted frequently. Misaimed lights are dangerous for on-coming vehicles.

Over time, the headlight lenses can deteriorate. They can become pitted due to abrasion caused by road sand and pebbles, and can crack, allowing water into the headlight. The reflector, made of vapourised aluminum deposited in a thin layer on a metal, glass or plastic substrate, can become dirty, oxidised or burnt and lose its brightness. This reduces the reflective strength.

If bulbs of higher-than-specified wattage are installed, it can cause damage to the vehicle’s electronic system which could be expensive to replace.