Fault Profile 2: RLS Rain/Light Sensor (RLSS Solar Rain/Light Sensor)

Rain/driving Light Sensor: Restrictions Due To Technical Features

- General information on initialization of the RLS:
An initialization of the RLS is only necessary after replacement of the windscreen or the RLS. From a technical perspective, the RLS cannot lose its initialization during operation. An improvement of the RLS by re-initialization is ineffective. A change can only be achieved by setting the sensitivity.

Automatic headlamp control
- During nice weather, the RLS switches the low-beam headlight on too early in the evening
- During nice weather, the RLS switches the low-beam headlight too late in the morning
- With poor visibility and bad weather, the RLS switches the low-beam headlight on too late

"Blue sky effect"
Two physical effects are responsible for these switching characteristics:
1. The spectrum of the ambient light ranges from ultraviolet light (UV light) through visible light, all the way to infrared light (IR light).

The driver switches the low-beam headlight on not only due to the current surrounding brightness but also due to a personal assessment of the current driving situation.

During good weather with a high UV proportion, the human eye takes account of the good visibility conditions.

This is why the driver switches the low-beam headlight off early in the morning and late in the evening despite low brightness.

During bad weather, the cloud cover filters the UV proportion of the ambient light. The driver takes account of the low visibility distance and switches the low-beam headlight on earlier despite adequate brightness. The currently is ineffective. A change can only be achieved by setting the sensitivity. used sensors that are suitable for automobiles measure the brightness in the range of visible light and partially in the range of infrared light. Due to the visibility conditions, they are unable to replicate human switching behaviour.

2. Due to the assembly position, the RLS does not receive adequate brightness when the sun is low.

The sensors for the automatic driving light switch are integrated in the rain sensor on the windscreen. The measured brightness in the sensor depends on the coverage angle and the direction of travel. When the sun is low, for example in autumn and winter, the brightness of the sun is not picked up. This means that the low-beam headlight remains on for a sustained period.

"Tunnel activation characteristics"
In brightly lit tunnels, the automatic headlamp control only switches on several seconds after entering the tunnel.
The intensity of the tunnel lighting is sufficient to delay the low-beam headlight activation.

Rain / driving light sensor on vehicles with Head-Up display
- In vehicles with the optional extra HUD, the RLS controls the brightness of the HUD. This requires a special direction of vision of one of the sensors. The behaviour on entering tunnels can therefore vary. The version for HUD cannot be replaced by the version without HUD.

Rain sensor
- RLS wipes without rain
- RLS does not wipe in the case of spray / drizzle
The function of the rain sensor is based on the principle of total reflection on the windscreen. Transmit diodes bundle IR light; the receiver diodes measure the reflected light.

With dispersion on the outside windscreen surface, the light volume received is reduced. The reduced light volume can be caused by precipitation on the windscreen, but also by soiling such as insects, dust or salt.

Furthermore, the spread of the precipitation can be very heterogeneous. On some types of vehicle, swirling leads to varying levels of moisture on the windscreen.

Extremely important is the condition of the wiper blades. Only if these reliably clean the windscreen can the remaining film of water be distinguished from new moisture.