For these reasons, HUDs typically incorporate glare shields and light traps intended to reject stray light. Assessing stray light issues (and any number of proposed solutions) before committing to physical hardware is complex, and requires the use of advanced modeling tools. Fortunately, these tools are available from ANSYS and allow problems to be rapidly identified. However, even if a problem is identified, an immediate solution might not be obvious.
Sébastien Abram, Product Owner HUD at ANSYS, explains: “Using ANSYS SPEOS® simulation, you will detect the issue on the virtual mock-up, but then it’s difficult to solve without reconsidering the complete design and layout of the system”. This is further complicated where small tweaks are made to internal components such as rotatable mirrors to match a given design to a particular windshield in a car. Unfortunately, small changes in the HUD’s internal geometry can have a disproportionate impact on stray light. According to Sébastien Abram, "after applying the Vantablack S-VIS to the housing of the HUD, even under the worst possible incident-light conditions, no more reflections were visible. It’s very close to the perfect conditions. Applying Vantablack appears to be a “miraculous” solution: it’s easy, quick and requires no change to the design or layout”.