How it works: lights that switch themselves on and off

Drivers can get used to it quickly: they put the lights into automatic mode and forget all about them. But how does it work? When do the lights switch themselves on and off? Let’s take a closer look at this “invisible” function with visible effects.

8. 9. 2020 Škoda World Innovation & technology

An automatic mode for lights is mandatory for new cars throughout the European Union. If drivers have this mode activated, they does not have to think about switching their lights on or off every time they drives. During daylight hours, their car’s lights function in daytime running lights mode.

“There are also regulations covering the time a car’s lights take to react to a change in the light conditions or switch from daytime to nighttime mode,” explains Boris Trávník, external vehicle lights electronics coordinator in Technical Development at ŠKODA.

How the automatic mode for lights works

When you enter a tunnel, for example, the daytime running lights switch to low beam within two seconds. A sensor behind the windscreen, either in the rearview mirror or in the middle of the dashboard, senses that the light conditions outside have changed and that nighttime mode is required. The type of sensor depends on the vehicle’s configuration.

Automatic light sensor

The sensor does not just control the car’s lights: it collects data for the windscreen wipers and air conditioning as well. The data are then evaluated by the BCM (Body Control Module), which is a control unit performing calculations and passing on instructions, e.g. to the headlights. The BCM is located beneath the dashboard, close to the fuse box. The RLFS sensor (RLSF is an abbreviation formed from the German words for rain, light, humidity and sun) in the rearview mirror picks up both light and energy in the infrared spectrum. By detecting refraction it can also tell whether it is damp outside or raining. Depending on the result, the sensor sends a clear instruction to the BCM whether to activate the lights and windscreen wipers or deactivate them.

The automatic lights mode and Full LED matrix headlights

The automatic lights mode makes life easier for drivers and lets them focus all their attention on their driving. “Unless there’s fog or heavy rain, drivers don’t have to worry whether they have switched their lights on or not or if they are using the right lights,” Boris Trávník says. “And at night the automatic mode adapts the lights’ functioning to the driving mode,” he adds, describing another function offered by modern Full LED matrix headlights on ŠKODA cars. These headlights ensure maximum visibility for the driver while preventing people in oncoming cars from being dazzled.

In most ŠKODA cars you activate the automatic regime by turning the lights control switch to AUTO. The fourth-generation OCTAVIA model has more automated lights, which are controlled by a “button module”. When the vehicle is parked, the lights can be in AUTO, low beam or outline lights mode or completely off. While driving, the driver can choose between AUTO and low beam. That ensures drivers don’t completely switch off the lights by mistake while driving. Whatever lights mode is activated when you turn the engine off, AUTO mode is activated automatically the next time you start the car.