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

22 points

3 hours ago

| 4 comments

Hi HN — author here. iesna.eu is a browser-based ecosystem for working with photometric data: parsing standard luminaire files (LDT/EULUMDAT, IES LM-63, Oxytech, ATLA-S001), running design calculations against EN 13201 / ANSI/IES RP-8 / CJJ 45 / IES-IDA MLO, and (the part I most want to show off here) rendering real urban scenes in Bevy with the photometric data driving actual streetlight behavior, including sky-glow contribution. The Skyglow Analysis demo loads a real LDT file into a Bevy scene (Khronos Bistro test asset). The luminaire's intensity distribution drives the streetlight rendering directly — no fudging — and the sky-glow grade updates live as you adjust the uplight percentage. Swap to a full-cutoff fixture and the sky goes from F (Severe) back to A (Excellent). You can see the difference on the buildings as well as in the sky. Stack: Rust core (eulumdat-rs and friends, ~20 crates handling photometric formats), Bevy for the 3D rendering, WASM for browser deployment. No backend; everything runs client-side. About a thousand lines of new code on top of the existing photometric library to make the Bevy integration work. Things I'd love feedback on:

The atmospheric scattering model is currently single-scattering Rayleigh+Mie. Is that defensible for the use case, or should I move toward multi-scattering? The Bistro test scene works well visually but isn't a controlled environment. Anyone know of a public urban geometry asset that's more typical of real road-lighting evaluation? The CJJ 45 implementation (China's national road lighting standard) is the only one I've had to reverse-engineer from translated PDFs. If anyone has primary-source experience with it, I'd value a sanity check.

Open-source on GitHub (eulumdat-rs and the related crates). Crates.io: eulumdat

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conartist6

10 minutes ago

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I love the idea, but it feels very un-serious as an attempt to educate people or reduce light pollution, which makes me very sad as someone who cares about reducing light pollution :'(

Why can't I create any light pollution no matter what I do? The stars wink out when the light pollution is 1000x less bright than the stars. It just feels completely disconnected from what I know light pollution feels like.

If I may make a technical suggestion, accurately representing the "qualia" of what both the presence and absence of colorful light feels like on a monitor requires compressing the color space a bit. Take a gander at this: https://brandonli.net/spectra/doc/

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holg

32 minutes ago

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Ok, even so the quality degrades a lot, i added the webgl2 version, it shall load as fallback, if webgpu is not enabled, but can as well be enforced, to see the difference:

https://iesna.eu/?wasm=skyglow_demo&force=webgl2

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holg

1 hour ago

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I should have mentioned: WebGPU is needed, on Safari there is a bug in the Bevy Overlay, so you only see flickering (very annoying!) This is an upstream issue (on to it) So FF and Chrome works fine (if WebGPU is enabled!)

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jeroenhd

1 hour ago

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All I get is an empty, dark blue page after I hit Launch Demo. Perhaps that does look a bit like a night sky, but I don't think that's what you're going for :)

Tested in Firefox/Brave/Chrome on Linux.

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holg

28 minutes ago

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https://iesna.eu/?wasm=skyglow_demo&force=webgl2, tested on wsl2 ubuntu, sorry linux machine in the office :D

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holg

1 hour ago

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Thanks for the information, i should have mentioned, webgpu is explicitly used here, and this might be the issue! Bevy's usage of WebGL2 is not that mature, and i use Bindless rendering (from my own contribution)...