Effective HUD Glass Inspection

It is widely known that HUDs – or automotive head-up displays – have already reached the status of being a billion-dollar market – and by 2026, this is predicted to expand by more than 24% CAGR.1 HUDs make vehicles safer and keep drivers focused on the road by displaying key data such as speed, navigation, and vehicle status directly in the driver’s line of sight.

The car’s windshield, as the canvas for HUD images, is, therefore, a critical optical component that requires careful testing. 

Head Up Display HUD System

A demonstration of Honda’s HUD System, showing all the different types of information that can be displayed to assist the driver. Video Credit: Honda

Due to the multiple layers of glass and film that make up today’s windshields, a windshield HUD system is complicated to design. The visual quality of a windshield HUD can be impacted by these layers, which can cause distortion or create duplicate overlapping images - called “ghost” images - of the projection if not formed and aligned properly.

For instance, safety glass is specifically designed with layers that make it less likely to break and cause injury. The two primary techniques for creating safety glass are tempering (hardening) and lamination (sandwiching a thin film between two thin glass layers).

Polyvinyl butyral (PVB) is typically the plastic layer that is used for automobile windshields. When designing the HUD, this layer must be taken into consideration.

Laminated glass (left) is less likely to shatter into pieces when damaged; tempered glass (right) breaks into small pieces rather than long, sharp shards that could cause serious injury.

Laminated glass (left) is less likely to shatter into pieces when damaged; tempered glass (right) breaks into small pieces rather than long, sharp shards that could cause serious injury. (Images: © Nuline Windows and Doors)

Projecting HUD Images on Automotive Windshields

There are four different surfaces in the windshield that can reflect virtual images with a PVB layer between two layers of glass: the front and the back surface of each glass layer. HUD windshields are made with a subtle wedge shape — the gap between the layers is tapered to correct for any duplicate image or “ghosting” effect. 2 

Windshield made from two glass layers and PVB without tapering (a) causes a ghosting effect. When the layers are tapered (b), preventing ghosting or double-image effects.

A windshield made from two glass layers and PVB without tapering (a) causes a ghosting effect. When the layers are tapered (b), ghosting or double-imafe effects are preventied. (Image Source)

Careful testing is required to ensure that HUD images project correctly through a car’s windshield. Typically, windshield testing employs imaging systems for visual inspection and isolates the properties of the HUD glass from the qualities of the HUD projector.

Automotive glass manufacturers are provided with critical information from experts in HUD glass testing and inspection about the layer properties, glass form, and wedge angle characteristics so that manufacturers can address issues in glass production and adjust their process.

The tooling and gauging experts at CP Industries have decades of experience engineering and delivering fully integrated test systems for windshield glass to the automotive industry.

As HUDs have become more prevalent in vehicles, the complexity of windshield glass test systems has increased. The automotive industry has become more regulated in terms of ensuring HUD visual quality and performance. Likewise, automotive OEMs have broadened their list of test and quality requirements for HUDs and the glass through which they are projected.

It is challenging for traditional inspection equipment and software to report an objective measure of HUD visual quality in alignment with the automotive industry and OEM specifications.

In the development of their next-generation HUD glass test system, the “HUDSON,” CP Industries wanted to optimize components that would both solve more customer challenges out of the box and address the advanced requirements of HUD glass inspection.

Optimal HUD Testing Solutions, From Radiant

It was determined by CP Industries that, thanks to Radiant’s industry expertise and novel solutions, their ProMetric® Imaging Systems and TrueTest Software platform offered the best solution.

The equipment and analyses Radiant has developed in the form of their HUD measurement solution already meet the HUD performance criteria that have been specified by the Society of Automotive Engineers (SAE J1757-2).

To meet specific OEM requirements and test parameters, the solution can be further engineered. An additional advantage of engineering is to permit integration with unique fixtures and automation controls.

CP Industries’ “HUDSON” HUD glass test system

CP Industries’ “HUDSON” HUD glass test system. (Image © CP Industries)

CP Industries engineered an automated 6-axis robotic arm system for their HUDSON inspection station with a ProMetric Y Imaging Photometer, TrueTest’s TT-HUD™ software module, and customized software elements unique to CP Industries’ test system and customer requirements, which were developed by Radiant for analysis and reporting. 

CP Industries’ new HUDSON test system has a fully-featured HUD measurement solution on board, which is already delivering performance and implementation time improvements – cutting their system delivery times from a 24-week average down to just 14 weeks.

CP Industries has also been able to realize a reduction in the amount of equipment needed for testing – for instance; there is no longer a need for a luminance meter to test projection light sources (a task that is now performed by the ProMetric Y Imaging Photometer).

Cycle times have also improved, at the same time as being able to take new measurements, like dynamic geometric measurement of HUD projections, which were not possible with their previous systems.

The CP Industries team outlines the mounting challenges they experienced in advanced HUD windshield testing and their solution development in this testimonial video. The team recounts the benefits of transitioning systems to Radiant’s complete HUD measurement solution -  combining electronic autofocus lenses, imaging photometers, and bespoke specially-developed HUD test software - from rudimentary machine vision.

They also share their experience collaborating closely with the Radiant team to provide next-level solutions to the automotive industry.


  1. Automotive Head-Up Display Market – Growth, Trends, COVID-19 Impact, and Forecasts (2021-2026), Mordor Intelligence, April 16th, 2021.
  2. Marcus, M., “Simultaneous head-up display windshield wedge-angle and layer-thickness measurements.” SPIE News, July 29th, 2016. 

This information has been sourced, reviewed and adapted from materials provided by Radiant Vision Systems.

For more information on this source, please visit Radiant Vision Systems.


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