Show HN: Browser-based light pollution simulator using real photometric data

Published: 3 days ago (May 2, 2026 at 05:08 AM EDT)

2 min read

Source: Hacker News

Overview

Hi HN — author here. iesna.eu is a browser‑based ecosystem for working with photometric data:

Parses standard luminaire files (LDT/EULUMDAT, IES LM‑63, Oxytech, ATLA‑S001)
Runs design calculations against EN 13201, ANSI/IES RP‑8, CJJ 45, and IES‑IDA MLO
Renders real urban scenes in Bevy with the photometric data driving actual street‑light behavior, including sky‑glow contribution.

The demo loads a real LDT file into a Bevy scene (Khronos Bistro test asset).

The luminaire’s intensity distribution drives the street‑light rendering directly — no fudging.
The sky‑glow grade updates live as you adjust the uplight percentage.
Swapping to a full‑cutoff fixture changes the sky from F (Severe) back to A (Excellent).
Differences are visible on both the buildings and the sky.

Rust core (eulumdat-rs and friends, ~20 crates handling photometric formats)
Bevy for 3D rendering
WebAssembly for browser deployment (no backend; everything runs client‑side)
~1 000 lines of new code on top of the existing photometric library to make the Bevy integration work

Atmospheric scattering model – currently single‑scattering Rayleigh + Mie. Is this defensible for the use case, or should I move toward multi‑scattering?
Test scene – the Bistro asset works visually but isn’t a controlled environment.
Urban geometry assets – anyone know of a public urban geometry asset that’s more typical of real road‑lighting evaluation?
CJJ 45 implementation – I’ve reverse‑engineered it from translated PDFs. If anyone has primary‑source experience with China’s national road‑lighting standard, I’d value a sanity check.