By: Linda Denner

Perfect Lighting Conditions

Machine vision system inspects vehicle interior lighting to ensure uniformity and absence of glare

source: Truck-Lite Europe

State-of-the-art interior lighting makes it possible for someone sitting in the passenger seat at night to look for an alternative route in a road atlas or read the newspaper to pass the time without irritating the driver. Machine vision system performs advance verification of lighting functionality and quality.


The ever-increasing quality and comfort expectations in the automobile industry now extend to something which you might think is quite simple, namely the interior lighting. A basic light source used to be sufficient, but in today's world interior lighting developers are being asked to take on new challenges. Ambient lighting built into the roof module, linear light strips mounted between the handgrips and lighting in the foot space and door pockets make it easier for passengers to get their bearings. In contrast, the reading light should be very bright, uniform and focused, illuminating a specific area without disturbing the driver's vision. Design, function and quality play a crucial role.

Designs based on a new generation of optical fiber systems and alternative light sources such as MPL (Modular Prismatic Light), MML (Modular Magnetic Light) and ELT (Electro Luminescence Technology) create opportunities to develop new lighting solutions in the car industry. Truck-Lite Europe develops and manufacturers this type of vehicle lighting. In order to comply with the quality specifications and meet the increasing function and design expectations, the company decided to introduce automated inspection in production. The intention was to provide objective, reproducible and complete quality control. To make the plan a reality, the company looked for a partner which has expertise in optical, non-contact inspection and measurement technology, and it selected Vision & Control which develops and produces machine vision systems in house.

Inspecting things that light up

The first step was to define the inspection criteria for the attributes which need to be checked by the machine vision system. The most important factor is proper functioning of the main components, namely the reading lights. Besides verifying that the various lights turn on and off, a check is made to ensure that the interior lighting turns on automatically when the doors are open (if that is desired). The ambient lights should stay illuminated as long as the headlights are switched on, which is another important criterion.

The proper functioning of the switches and buttons also has to be verified. This includes the reading light on/off button and the selector switch which the driver sets to control whether the interior lighting is turned on automatically when the doors are opened. The switch systems with backlighting are checked as well.

Besides functionality, design also plays an important role. The lighting has to blend in seamlessly with the vehicle ambience.

The color nuance of the module is detected with the aid of a high-resolution color camera. Depending on the type, special design elements such as grills and recesses also need to be considered.

Not everyone realizes that the roof lighting not only provides optimal illumination but also ensures that phone calls can be made without noise and interference. The microphones for the hands-free system are mounted in this element. A suitable combination of fabric and paper non-woven materials makes it possible to have a pleasant conversation without annoying vehicle noise. This configuration is also included in the inspection criteria.

Following initial joint lab investigations at the Vision & Control Application Lab, a set of machine vision components was selected as a platform for dependable evaluation of all the inspection and test criteria. The Vision & Control vicosys® multi-camera system in combination with a 4 MP color camera and high-resolution optics checks compliance with all of the criteria and reports minute deviations from spec even if they are only minute.

100% quality control

High-performance vicolux® LED lighting together with an FDLKD11 camera view provides a uniform source of incident light for the entire roof module surface. All lighting components, buttons and switches as well as design features such as color appear in their true light. An additional light source shining from the opposite direction provides the uniform area lighting needed to inspect the elements of the hands-free system.


High-performance vicolux® LED lighting with FDLKD11 camera view provides a uniform source incident light for the roof module surface.

In combination with a 4 MP color camera and high-resolution optics, the vicosys® multi-camera system checks vehicle interior lighting.

Working together with the Vision & Control service team, Truck-Lite integrated the components into its production line. Using the extensive vcwin® machine vision library, the complex inspection & test catalogue was translated into an inspection & test sequence for 100% quality control.

Components supplied by Vision & Control create the basis for objective, reproducible, automated quality control. The Vision & Control parameterization interface provide access to an extensive machine vision library which gives users everything they need to carry out the current inspection & test sequence and make modifications to meet future needs.

Successful rollout of the new quality assurance process depended on more than the hardware alone. Close collaboration with the Truck-Lite Europe production engineering team was needed to put a system in place which reliably checks compliance with the full set of criteria. Machine vision training was also held on site. The team at Truck-Lite Europe is now able to optimize and upgrade the system without outside assistance.

Specialist article appeared in messtec drives AUTOMATION 8/2013