Rain/Driving Light Sensor: Restrictions Due to Technical Features

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 driving lights control
- During nice weather, the RLS switches the driving light on too early in the evening- During nice weather, the RLS switches the driving light off too late in the morning- With poor visibility and bad weather, the RLS switches the driving light on too late

"Blue sky effect"
Two physical effects are responsible for these two 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 driving light 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 driving light 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 driving light on earlier despite adequate brightness. The currently 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 behavior.
2. Due to the installation 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 driving light remains on for a sustained period.

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

Rain / 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 behavior on entering tunnels can therefore vary. The version for HUD cannot be renewed 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 quantity received is reduced. The reduced light quantity 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.