Lightmatch: Bridging the optical gap between mock-up and production in automotive lighting

In automotive lighting development, micro-optical features are increasingly used to enable new design possibilities:

• ultra-thin light guides
• controlled diffusion
• beam shaping
• light curtain effects
• homogeneous illumination without additional components

By integrating optical functionality directly into injection moulded surfaces, engineers can achieve lighter architectures, improved efficiency, and reduced system complexity — all critical factors in today’s landscape. However, this shift towards micro-structured optics introduces a rarely discussed but highly impactful problem across the development chain: The optical behaviour of your prototype may have some diferences from your final injected part. And most decisions are still made based on it.

The hidden discontinuity in the development loop

From concept to SOP, the typical development flow of an optical surface looks like this:

1. Micro-optical concept design
2. Optical simulation
3. PMMA mock-up prototype
4. Prototype validation
5. Production mould manufacturing
6. Injection
7. Final photometric validation

At the prototype stage, the micro-optical design is usually engraved directly onto a machined PMMA mock-up. This allows lighting engineers to illuminate the surface and validate performance early in the project timeline. So far, so good. But months later — once the production mould is manufactured and engraved, and the first injected parts are measured — a familiar situation often occurs: The injected part does not behave photometrically exactly like the validated prototype. Even when the same micro-optical design is used.

Why prototype and production don’t correlate

This mismatch is not a design flaw. It is the result of two fundamentally different manufacturing realities: 1. Direct engraving on PMMA prototype The femtosecond laser interacts directly with the PMMA surface, generating a specific micro-geometry and surface finish under highly controlled conditions. This becomes the reference used for early optical validation. 2. Engraving on steel + injection replication In production, the same micro-optical geometry is engraved into hardened steel inserts. From there, the final optical surface is not created by the laser — but by the injection process itself. This introduces:

• surface finishing differences
• replication limitations
• material flow behaviour
• process parameter sensitivity
• local shrinkage effects
• micro-structure fidelity loss

The injected PMMA must now copy a steel-textured surface under thermal and pressure constraints. And this copy is rarely perfect. As a result, the optical output of the injected part may deviate from the validated prototype — sometimes by double-digit percentages in luminance distribution.

The cost of late optical reality

At this stage of the project, the implications are well known to both Tier 1 and OEM engineering teams:

• mould modification loops
• optical redesign iterations
• supplier realignment
• tooling rework
• development delays
• SOP pressure escalation

Each correction cycle at mould stage can cost:

• several thousand euros
• multiple weeks of lead time
• additional coordination across optical, tooling and injection partners

And more critically: These decisions are now made under production timing pressure.  

Introducing Lightmatch: correlation months earlier

Lightmatch was developed to answer a simple but crucial question much earlier in the project: Will this micro-optical concept behave the same once injected? Instead of validating only a directly engraved prototype, Lightmatch replicates both manufacturing paths in parallel during the early prototype phase.

A selected optical area of the part is:

• simulated under its real lighting conditions
• engraved directly on PMMA (prototype path)
• engraved into steel inserts
• injected using a controlled mould

This results in:

• a mock-up sample identical to today’s prototype validation
• an injected sample manufactured through a production-equivalent process

Both are then analysed through:

• confocal microscopy (tolerance and geometry verification)
• photometric testing
• visual appearance assessment

And compared against simulation.

From hope-based validation to predictable production

By introducing injection-representative optical behaviour months before hard tooling decisions are made, Lightmatch enables:

• earlier design adjustments
• injection-aware optical validation
• reduced mould modification risk
• compressed development loops
• fewer late-stage surprises

All without SOP timing pressure. In many cases avoiding a single mould correction loop offsets the full Lightmatch development effort.

A decision-making tool, not a prototype replacement

Lightmatch does not replace optical simulation or traditional prototyping. It complements them by introducing production-relevant information at a stage where design flexibility still exists. For Tier 1 and OEM teams working with micro-optical surfaces, this means decisions can be based not only on how a design performs when engraved directly on PMMA — but on how it will behave once injected in series production. And in today’s compressed automotive development cycles, having the right information earlier is often the difference between late redesign or fist-time-right tooling.