Show HN: Browser-based light pollution simulator using real photometric data | Hacker News Reader

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

iesna.eu

44 pointsholg20 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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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/

I suspect that another part of it is that you're accounting for the effect of the lights in the scene on the sky, but very few of the lights involved in light pollution will be lights that you can directly see -- the only evidence they exist will be from their upward scattering.

So here's the suggestion: there should be a "number of upward lights" slider which should influence an atmospheric light haze shader which, like real light pollution is brightest near the horizon. Then you could use a relatively real stellar skymap and give a sense of what it feels like to lose sight of the heavens, which is a kind of shocking thing to see, as well as what it might take to fix it.

That's the real good proposal. I must admit, my focus was on the street lights, which in general are already almost good, compared to what you mention Thanks a lot

Yeah the streetlights are great with that sodium carbide feeling. Having the sodium carbide horizon blend in with the sodium carbide buildings and trees and lamps will really sell the effect

Yup, so actually my take as well is, the scene itself is imperfect, i took some known and easy to implement one. So some scene, where some high building is illuminated up, would be desirable...

Love this tool - actually the idea itself - since I am fighting heavily against unnecessary outdoor lighting, especially with the new LED lights which I find terribly disturbing.

Thanks, well i got more feedback, so i figured out it shall be done even better...

That's very cute, I like the idea. Did you consider upgrading to a dynamic perspective? I guess that would be cooler and more immersive.

That's the neat idea!

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

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!)

You’re going to get a lot of mobile iPhone users disappointed, since the main browser engine even in HN apps is Safari. Maybe a warning would encourage them to try the site elsewhere instead of closing it in disappointment?

i agree, sorry this is some edge-tech, so for safari it is a bit tricky, as it reports to have webgpu, but &force=webgl2 will do the trick. I am working on the fix to have webgpu behave properly on Safari

Safari bug should be fixed with https://commits.webkit.org/313133@main - please feel free to file WebGPU WebKit bugs at https://bugs.webkit.org/enter_bug.cgi?product=WebKit&GoAhead... if you run across any

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.

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)...

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

That works great, thanks!

Thanks for your interest :D

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