Modern Automotive Display Touch-Lens Interface: Page 4 of 5

December 13, 2012 //By Paul Weindorf, James Kornacki, Visteon Corporation
Modern Automotive Display Touch-Lens Interface
The center stack panel area of today’s vehicles has become the integration site for many occupant interface technologies and is being driven by consumer requirements influenced by today’s personal electronic devices.
amount of antireflective films or antiglare treatments can solve the sunlight specular angle problem since the luminance of the sun is approximately 1.6x109 cd/m2.

To determine required display luminance, the reflection components must first be assessed from various sources per Figure 8.


Figure 8: Superposition of Reflection Components [1]


Since superposition applies, the process involves considering each source separately to obtain the total background reflection luminance. These three major lighting conditions must be considered:

1. Hemispherical illumination – from the cockpit interior where the diffuse reflectance of the display may be estimated by using an integrating sphere specular component excluded (SCE) measurement.

2. Specular illumination – from sources like white shirt, seats, etc. Once the specular reflectance, ζ, for the system is measured, the specular object luminance seen by the driver can be calculated per Equation 1.

3. Direct sunlight illumination of the display – The haze reflection component (Figure 9) is perhaps the least understood component of reflection and is the cause of many poor visibility implementations.


Figure 9: Reflection Components [2, page 188]


Using a classical Bi-Directional Reflection Distribution Function (BRDF) method to measure the reflectance as a function of angle from the specular position can cause the some of the reflection components (shown in red per Figure 10) to miss the detector due to multiple reflection surfaces.


Figure 10: BRDF Apparatus [1, page 230 adapted]


A more suitable method is to use a small signal reflection measurement method, shown in Figure 11, where the collimated light source beam size is large enough to encompass all of the reflection surfaces in the optical stack.


Figure 11: Small Signal Reflection Measurement Method [2]



Figure 12: Goniometric Small Signal Measurement System


Figure 12 shows a goniometric apparatus to measure the small signal reflection with example results per Figure 13.


Figure 13: Small Signal Measurement Example

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