The RLT IC (Rain Light Tunnel Sensor) is intended for controlling an optical sensor unit in automotive wiping systems or in industrial camera and window systems. A special, high-sensitive receiver allows processing of a diode input signal without total reflection of the send signal, allowing reliable detection of rain and water drops. Due to the used HALIOS-SD (Sigma Delta) measurement method a very high robustness against ambient influences like sunlight, any kind of flickering light, aging and dirt is provided.



  • Wiper control according to rain intensity
  • Control of the automatic vehicle lighting
  • Measuring of the solar load in vehicle
  • Control of the head-up-display illumination


  • High light immunity
  • Independent weather conditions (differentiation rain, ice and snow)
  • Low latency
  • Best function to cost ratio

Use Case


Wiper control with Rain-Light Sensor Interface IC


Detection sensity - even through distratction by ambient light, dirt, amount of water on sensor

Elmos Expertise in Optical Sensor Interface ICs


  • DC current cancellation
  • High light suppression via HALIOS® technology
  • Scalable sensor detection area
  • Lowest system latency
  • Four logarithmic input channels for ambient light measurements
  • Internal temperature sensor


  • Automotive qualified (AEC-Q100) with proven track record over vehicle lifetime
  • Highest robustness in automotive environment over vehicle lifetime
  • Best-in-class ambient light immunity due to HALIOS® technology
  • Long time stability due to compensation of LED or PD ageing
  • Diagnostic and monitoring functions to minimize salt, dirt or scratches within the sensor active area


  • Adaptable sensor system detection area
  • Self-calibration makes the sensor solution scalable to different car platforms (e.g. different windshield glasses)
  • Sensitivity adjustment via configuration

Our Solution

About – E527.04 Rain-Light Sensor Interface IC

Infrared based HALIOS® Rain-Light IC providing best sensitivity detecting heavy fog or light rain for improved wiper control. The solution is immune against ambient light enabling robust sensor design.

Advantages / USPs

  • Lowest sensor system cost
  • Best in class sunlight rejection
  • Sensor interface with lowest latency
  • Scalability across different car platforms (2LED+1PD up to 6LED+1PD)
  • Sensor size and weight
  • Sensor fusion (rain, ambient light, front light, sun load, humidity, head-up-display brightness)
  • Sensor Robustness (no activation of wiper system due to e.g. dirt, salt, etc.)

Comparison of E527.04 vs. competitor’s approach

Elmos: HALIOS® Differential Measurement

Competitor: Absolute Measurement

+ Extremely high sensitivity for small rain drops
+ Very high robustness against flickering light and reflections of rain drops at night
+ Reduced software support due to easy implementation of calibrations procedures
+ Good sensitivity for water films
– Needs high resolution of the PD signal
– Needs good temperature drift and offset compensation
– Needs dedicated optics and optical path design


Our Solution - System Constellation

Simple System

Lower range vehicles

  • System cost
  • Standard sensitivity

Performance System

Mid range vehicles

  • Automatic wiping + lighting
  • Faster wiper reaction time
  • Higher sensitivity

High End System

Luxury vehicles

  • Sensor fusion (humidity, distance)
  • Precise meas. for wiping, HUD, AC
  • Dirt, salt, ice, spray detection

Bar recognition area

  • 1 x E527.04
  • 2 x LEDs
  • 1 x Photodiode

Semicircle detection area

  • 1 x E527.04
  • 4 x LEDs
  • 1 x Photodiode

Circle recognitionn area

  • 1 x E527.04
  • 6 x LEDs
  • 1 x Photodiode


Can also a water flush on the windshield be detected?

Yes, even a water film will be detected since it is not complete homogenous and due to the high sensitivity of HALIOS® sensor the small changes in the water film will cause a signal.

How many LEDs per sending path are needed?

Optical simulation have shown good results with 4 LEDs per sending paths. But also 3 LEDs or even less can be sufficient. That depends on requirements of the complete system.

Can also a LED used instead of a photo diode?

Yes, our measurements have shown good results when using  a LED as the receiving device.

Can you recommend LED and photo diode components?

In general, the selection of the IR LEDs are strongly dependent on the application, screen-size and features  (power, emitter angle, etc.). For most applications we successfully worked with Osram IR-LEDs (SFH4250, SFH4253, SFH4243) or Vishay (VSMF9700, VSMF3710) and Osram photo diodes (SFH2400FA, TEMD7100).

How does the thickness of the window shield influences the sensor?

In our setup a window shield thickness of  5.2mm to  max 6.3mm showed good results. Smaller thicknesses are possible with a changed sensor design.

Are there design recommendations for the placing of the sending LEDs?

The LEDs should be placed in circle around the receiving device. For our setting a radius of 12mm gave the best results. But that should be verified for every setting because the used LEDs PD and of course the housing of the sensor have an impact to that parameter.

How many LEDs are required for a good rain sensor design?

The amount of LEDs strongly depend on the customer requirement (specified detection area on windshield). With an optics only 2-4 LEDs are required.



  • Info Sheet - E527.04
  • Fighting Guide


If you have any questions, don't hesitate to contact us