# Lossy-metal half-space reflectance vs Tidy3D

<span class="validation-badge">validated · 2026-08-28</span>

<div class="case-meta"><span>forward</span><span>resolution 1</span><span>parity</span><span>p1</span><span>metal</span><span>conductor</span><span>tidy3d_golden</span><span>high_yield</span></div>

This case compares a local FDTDX result with pinned reference data generated by Tidy3D.

```{figure} ../../_static/generated/material_models.svg
:alt: Technical schematic associated with Lossy-metal half-space reflectance vs Tidy3D

Representative dispersive material response.
```

## What is exercised

High-σ half-space should be nearly perfectly reflecting. T=S_T/S0, R=1-T.

This case runs at its declared full benchmark resolution (resolution factor 1.0).



## Recorded result

| Metric | Observed / error | Reference / limit | Error | Effective budget | Result |
|---|---:|---:|---:|---:|---:|
| `reflectance_R` | 1 | 0.999973 | 2.730e-05 | 0.0399995 | <span class="metric-pass">PASS</span> |

The table is rendered from `progress.json`; it is not a hand-written success claim. For metrics that report an error directly, the “observed” column repeats that error and the reference column is the acceptance threshold.

## Reproduce

```bash
uv run fdtdx-bench run --case parity_metal_reflect
```

Implementation and provenance: `benchmarks/cases/parity_metal_reflect/case.yaml`, `benchmarks/cases/parity_metal_reflect/run.py`, `benchmarks/goldens/parity_metal_reflect.npz`.

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