The ghost image problem in automotive HUDs
Head-up displays project information onto the windshield, reflecting from the inner glass surface into the driver's line of sight. But a windshield is a multi-layer structure — outer glass, PVB interlayer, inner glass — and each interface produces a secondary reflection. These secondary reflections create a displaced "ghost" image that overlays the primary HUD image, reducing readability and distraction safety.
Ghost images are most visible in high-brightness HUD systems and augmented reality HUDs (AR-HUDs) where the virtual image must be spatially precise. As the automotive industry moves toward larger HUD projection areas and AR overlay, ghost suppression becomes a critical optical requirement rather than a nice-to-have.
How AR coatings eliminate ghosting
Anti-reflective coatings applied to the inner glass surface suppress the secondary reflection that creates the ghost. By reducing the reflectivity of the relevant interface from approximately 4% to below 1%, the ghost image becomes invisible to the driver. Simultaneously, the primary HUD image becomes brighter because less projection energy is lost to reflections.
Kriya's AR coatings for HUD applications use multi-layer stacks with RI values from 1.16 to 1.95, enabling precise spectral tuning. The AR effect is optimised for the specific wavelengths used by the HUD projector — typically green, red, and blue LED or laser sources — rather than applying a generic broadband AR that wastes performance budget on irrelevant wavelengths.
Spectral tuning for HUD wavelengths
Different HUD systems use different light sources with specific emission spectra. Kriya's tuneable RI platform enables the AR stack to be optimised for:
- Monochromatic HUDs — single-wavelength optimisation for maximum ghost suppression at the projection wavelength
- Full-colour HUDs — multi-band AR covering RGB emission peaks
- AR-HUDs — broadband coverage for augmented reality overlay across the visible spectrum
The wide RI range (1.16 to 1.95) available in Kriya's PFAS-free platform enables stack designs that competitors — limited to narrower RI ranges — cannot match in a single supplier system.
HUD brightness enhancement
Beyond ghost suppression, AR coatings improve HUD efficiency by increasing the fraction of projected light that reaches the driver. Every reflection at the windshield surfaces represents lost brightness. A well-designed AR stack can increase effective HUD brightness by 5 to 10%, which translates to either better readability in sunlight or lower projector power consumption.
Integration with automotive glazing
Kriya's HUD AR coatings are compatible with standard automotive glazing production:
- Applied to glass surface before lamination — compatible with existing windshield production lines
- Sol-gel chemistry — thermally cured, creating a durable oxide film that survives the lamination process
- Compatible with PVB interlayer bonding — no delamination risk at the coating interface
- Can be combined with Kriya's ATO solar heat control in the same windshield for combined HUD optimisation and thermal management
The smart cockpit vision
HUD anti-ghosting is one element of the broader smart cockpit transformation. As vehicles evolve toward glass-as-display interiors with seamless, buttonless surfaces, optical coatings become the enabling material layer. Kriya's platform supports:
- HUD anti-ghosting and brightness enhancement
- Interior decorative trims with deep-black appearance and optical windows for embedded sensors
- Anti-reflective coatings for instrument cluster cover glass
- Anti-smudge and anti-fingerprint surfaces for touch interfaces