# Latest

**URL:** https://discourse.radiance-online.org/latest.md

[Latest](https://discourse.radiance-online.org/latest.md) · [Categories](https://discourse.radiance-online.org/categories.md)

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## [Welcome to the Radiance Forum!](https://discourse.radiance-online.org/t/welcome-to-the-radiance-forum/8)

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**Author:** [@system](https://discourse.radiance-online.org/u/system)\
**Replies:** 0\
**Last updated:** [May 1, 2018, 10:19pm UTC](https://discourse.radiance-online.org/t/welcome-to-the-radiance-forum/8 "2018-05-01T22:19:27Z")

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Welcome to the Radiance Forum! This site is exclusively for users and developers of LBNL’s Radiance lighting simulation software and related packages. Here is where the experts gather, and where you can become an expert…

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## [Spectral simulation with photon mapping in Radiance 6](https://discourse.radiance-online.org/t/spectral-simulation-with-photon-mapping-in-radiance-6/7060)

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**Author:** [@Rita\_Alwalidi](https://discourse.radiance-online.org/u/Rita_Alwalidi)\
**Replies:** 3\
**Last updated:** [November 1, 2026, 5:49pm UTC](https://discourse.radiance-online.org/t/spectral-simulation-with-photon-mapping-in-radiance-6/7060 "2026-11-01T17:49:25Z")

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Hello Radiance community, I am currently modelling a xenon solar simulator with a parabolic specular reflector. Without photon mapping, the parabolic reflector does not contribute to the irradiance at the target. There…

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## [OptiX error for RTX5080](https://discourse.radiance-online.org/t/optix-error-for-rtx5080/6966)

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**Author:** [@Byron](https://discourse.radiance-online.org/u/Byron)\
**Replies:** 14\
**Last updated:** [October 28, 2026, 2:53pm UTC](https://discourse.radiance-online.org/t/optix-error-for-rtx5080/6966 "2026-10-28T14:53:11Z")

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Good evening, I am not sure how active this section of the forum is, but I have a question regarding accelerad. I have been using this for years, and specifically the AcceleradRT functionality. Recently I bought myself…

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## [Issue with the New source.cal File in Electric Lighting Calculations](https://discourse.radiance-online.org/t/issue-with-the-new-source-cal-file-in-electric-lighting-calculations/7064)

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**Author:** [@Majid\_Miri](https://discourse.radiance-online.org/u/Majid_Miri)\
**Replies:** 4\
**Last updated:** [October 27, 2026, 10:03pm UTC](https://discourse.radiance-online.org/t/issue-with-the-new-source-cal-file-in-electric-lighting-calculations/7064 "2026-10-27T22:03:26Z")

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Hi Greg, I recently performed a simple lighting calculation using the latest Radiance binaries and cal files for a scene containing 10 electric lighting fixtures. I noticed that the results obtained with the new source.…

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## [5 Phase method sDA analysis](https://discourse.radiance-online.org/t/5-phase-method-sda-analysis/7063)

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**Author:** [@Vin](https://discourse.radiance-online.org/u/Vin)\
**Replies:** 0\
**Last updated:** [October 22, 2026, 10:45pm UTC](https://discourse.radiance-online.org/t/5-phase-method-sda-analysis/7063 "2026-10-22T22:45:40Z")

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Hi all, I am seeking to do an sDA analysis on an IFC model of a building. Given there have been many changes to radiance since 2017, is this tutorial still the most current for a 5 phase method to do a spatial daylight…

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## [New WGMDfunc material type](https://discourse.radiance-online.org/t/new-wgmdfunc-material-type/6735)

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**Author:** [@Greg\_Ward](https://discourse.radiance-online.org/u/Greg_Ward)\
**Replies:** 10\
**Last updated:** [October 16, 2026, 4:50pm UTC](https://discourse.radiance-online.org/t/new-wgmdfunc-material-type/6735 "2026-10-16T16:50:55Z")

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Dear All, Just last week, I introduced a new programmable material type to Radiance 6.0a. Its design provides greater control over different components in the Ward-Geisler-Moroder-Dür model that underpins the existing p…

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## [Colorspace transformations](https://discourse.radiance-online.org/t/colorspace-transformations/7061)

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**Author:** [@Nathaniel\_Jones](https://discourse.radiance-online.org/u/Nathaniel_Jones)\
**Replies:** 1\
**Last updated:** [October 14, 2026, 7:26pm UTC](https://discourse.radiance-online.org/t/colorspace-transformations/7061 "2026-10-14T19:26:42Z")

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I’m trying to calibrate several different monitors such that images rendered on them will match the color of a physical sample under room lighting. As I understand it, this requires that I correct the coloring of the ima…

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## [Call Postdoctoral Fellowship "Translational research in daylighting for human health and well-being" at ETH Zürich, Departmenf of Architecture](https://discourse.radiance-online.org/t/call-postdoctoral-fellowship-translational-research-in-daylighting-for-human-health-and-well-being-at-eth-zurich-departmenf-of-architecture/7053)

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**Author:** [@Lars\_Grobe](https://discourse.radiance-online.org/u/Lars_Grobe)\
**Replies:** 0\
**Last updated:** [August 27, 2026, 11:24am UTC](https://discourse.radiance-online.org/t/call-postdoctoral-fellowship-translational-research-in-daylighting-for-human-health-and-well-being-at-eth-zurich-departmenf-of-architecture/7053 "2026-08-27T11:24:51Z")

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Daylight Integration Nexus is hiring! The Department of Architecture (D-ARCH) ETH Zurich invites an excellent postdoctoral fellow for 18 months to take the next step in his or her career, forming an independent research …

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## [Radiance Workshop 2026 - Program](https://discourse.radiance-online.org/t/radiance-workshop-2026-program/7050)

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**Author:** [@Mehlika\_Inanici](https://discourse.radiance-online.org/u/Mehlika_Inanici)\
**Replies:** 0\
**Last updated:** [July 28, 2026, 3:34am UTC](https://discourse.radiance-online.org/t/radiance-workshop-2026-program/7050 "2026-07-28T03:34:46Z")

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Dear all, The program for this year’s workshop is (likely) finalized. It is a great lineup of presentations; we hope you can join… International Radiance Workshop 2026

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## [What is the correct luminous efficacy ratio for genssky input illuminances?](https://discourse.radiance-online.org/t/what-is-the-correct-luminous-efficacy-ratio-for-genssky-input-illuminances/7049)

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**Author:** [@NimaForouzandeh](https://discourse.radiance-online.org/u/NimaForouzandeh)\
**Replies:** 2\
**Last updated:** [July 21, 2026, 8:03pm UTC](https://discourse.radiance-online.org/t/what-is-the-correct-luminous-efficacy-ratio-for-genssky-input-illuminances/7049 "2026-07-21T20:03:10Z")

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Hi all, genssky needs global horizontal illuminance and global horizontal illuminance as its inputs. Yet in most station data, only irradiance values are available. There are several luminous efficacy ratios one can as…

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## [Public GitHub Release: Horticulture Lighting Simulator, powered by Radiance](https://discourse.radiance-online.org/t/public-github-release-horticulture-lighting-simulator-powered-by-radiance/7041)

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**Author:** [@Achievable](https://discourse.radiance-online.org/u/Achievable)\
**Replies:** 3\
**Last updated:** [July 5, 2026, 11:28pm UTC](https://discourse.radiance-online.org/t/public-github-release-horticulture-lighting-simulator-powered-by-radiance/7041 "2026-07-05T23:28:10Z")

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Hi everyone, I’m excited to share the public GitHub release of a project I’ve worked on for quite a while: Horticulture Lighting Simulator A Radiance-based horticultural lighting simulation and 3D visualization engine…

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## [Converting genssky output to Watts per wavelength band](https://discourse.radiance-online.org/t/converting-genssky-output-to-watts-per-wavelength-band/7043)

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**Author:** [@Nathaniel\_Jones](https://discourse.radiance-online.org/u/Nathaniel_Jones)\
**Replies:** 6\
**Last updated:** [June 29, 2026, 3:46pm UTC](https://discourse.radiance-online.org/t/converting-genssky-output-to-watts-per-wavelength-band/7043 "2026-06-29T15:46:07Z")

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Is there any guidance on how to convert the radiance values from genssky to units of power? I usually use the assumption of 179 lumens per Watt in Radiance, but that assumes the powers in each channel to have been added …

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## [How to Efficiently Capturing Partially Occluded Direct Solar Contributions in Enhanced Two-Phase Daylight Simulation](https://discourse.radiance-online.org/t/how-to-efficiently-capturing-partially-occluded-direct-solar-contributions-in-enhanced-two-phase-daylight-simulation/7045)

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**Author:** [@1112](https://discourse.radiance-online.org/u/1112)\
**Replies:** 1\
**Last updated:** [June 27, 2026, 3:55pm UTC](https://discourse.radiance-online.org/t/how-to-efficiently-capturing-partially-occluded-direct-solar-contributions-in-enhanced-two-phase-daylight-simulation/7045 "2026-06-27T15:55:23Z")

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I used the enhanced two-phase method to calculate vertical illuminance and found that some results were biased compared with the HDR-derived values rendered using rpict. At first, I assumed that this discrepancy was caus…

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## [Calls for Abstracts: 24th Radiance Workshop in Seattle, WA](https://discourse.radiance-online.org/t/calls-for-abstracts-24th-radiance-workshop-in-seattle-wa/7024)

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**Author:** [@Mehlika\_Inanici](https://discourse.radiance-online.org/u/Mehlika_Inanici)\
**Replies:** 3\
**Last updated:** [June 15, 2026, 5:56pm UTC](https://discourse.radiance-online.org/t/calls-for-abstracts-24th-radiance-workshop-in-seattle-wa/7024 "2026-06-15T17:56:49Z")

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This year’s event will take place at the University of Washington, in Seattle, Washington, USA, between August 31 – September 2, 2026. Following the typical format, two days will be the Radiance Workshop (seminars) and …

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## [Gensdaylit: a spectral, penumbra-aware extension of gendaylit](https://discourse.radiance-online.org/t/gensdaylit-a-spectral-penumbra-aware-extension-of-gendaylit/7038)

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**Author:** [@Funerus](https://discourse.radiance-online.org/u/Funerus)\
**Replies:** 0\
**Last updated:** [June 10, 2026, 9:36pm UTC](https://discourse.radiance-online.org/t/gensdaylit-a-spectral-penumbra-aware-extension-of-gendaylit/7038 "2026-06-10T21:36:33Z")

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Dear Radiance users, I am sharing some of our recent work that may be of interest to those in the photovoltaics (PV) sector, or anyone running thermal studies that require spectrally-resolved simulations beyond the visi…

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## [BTDF Luminit file to BSDF.xml](https://discourse.radiance-online.org/t/btdf-luminit-file-to-bsdf-xml/7025)

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**Author:** [@Alexmb](https://discourse.radiance-online.org/u/Alexmb)\
**Replies:** 7\
**Last updated:** [May 25, 2026, 9:59am UTC](https://discourse.radiance-online.org/t/btdf-luminit-file-to-bsdf-xml/7025 "2026-05-25T09:59:30Z")

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Hello, I am trying to use Luminit diffuser data (BTDF & BSDF Data | Luminit Optical Diffuser Performance). The workflow I am currently following is: Start from the Luminit file BTDF\_2.bsdf.txt . Read the angular BTDF…

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## [Issue with Spectral Matrix Simulation](https://discourse.radiance-online.org/t/issue-with-spectral-matrix-simulation/7007)

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**Author:** [@Hasti](https://discourse.radiance-online.org/u/Hasti)\
**Replies:** 4\
**Last updated:** [April 29, 2026, 1:44am UTC](https://discourse.radiance-online.org/t/issue-with-spectral-matrix-simulation/7007 "2026-04-29T01:44:06Z")

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Hello, I am relatively new to the world of Radiance and am currently learning and testing its commands. I have encountered an issue in the spectral matrix simulation section, and I would greatly appreciate any guidance …

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## [A high performance dctmestep](https://discourse.radiance-online.org/t/a-high-performance-dctmestep/7012)

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**Author:** [@1112](https://discourse.radiance-online.org/u/1112)\
**Replies:** 10\
**Last updated:** [April 23, 2026, 1:10pm UTC](https://discourse.radiance-online.org/t/a-high-performance-dctmestep/7012 "2026-04-23T13:10:54Z")

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I have implemented a highly optimized version of dctimestep, achieving a significant performance increase (an 8x to 34x speedup). The primary modifications are as follows: Memory-Mapped I/O: The daylight coefficient HD…

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## [Browser-based horticultural lighting simulation on Radiance — photon-native PPFD, concentric-ring layout + basis-matrix solver — seeking technical feedback](https://discourse.radiance-online.org/t/browser-based-horticultural-lighting-simulation-on-radiance-photon-native-ppfd-concentric-ring-layout-basis-matrix-solver-seeking-technical-feedback/6995)

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**Author:** [@Achievable](https://discourse.radiance-online.org/u/Achievable)\
**Replies:** 7\
**Last updated:** [April 14, 2026, 4:45am UTC](https://discourse.radiance-online.org/t/browser-based-horticultural-lighting-simulation-on-radiance-photon-native-ppfd-concentric-ring-layout-basis-matrix-solver-seeking-technical-feedback/6995 "2026-04-14T04:45:45Z")

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Hi everyone, I’ve been building a browser-based horticultural lighting simulation tool on top of Radiance and wanted to share the details here for feedback from people with more Radiance experience than I have. The tool…

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## [Three Phase Matrix Method using irradiance](https://discourse.radiance-online.org/t/three-phase-matrix-method-using-irradiance/6999)

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**Author:** [@Terrance\_McMinn1](https://discourse.radiance-online.org/u/Terrance_McMinn1)\
**Replies:** 4\
**Last updated:** [April 12, 2026, 12:42pm UTC](https://discourse.radiance-online.org/t/three-phase-matrix-method-using-irradiance/6999 "2026-04-12T12:42:17Z")

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In understanding Subramaniam paper “Daylighting simulations with radiance using matrix-based methods”, and his accompanying document (https://www.radiance-online.org/learning/tutorials/matrix-based-methods), I have a que…

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## [Weighting factors used in the irradiance	calculation](https://discourse.radiance-online.org/t/weighting-factors-used-in-the-irradiance-calculation/2922)

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**Author:** [@Parisa\_Khademagha](https://discourse.radiance-online.org/u/Parisa_Khademagha)\
**Replies:** 20\
**Last updated:** [April 7, 2026, 6:44am UTC](https://discourse.radiance-online.org/t/weighting-factors-used-in-the-irradiance-calculation/2922 "2026-04-07T06:44:07Z")

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Dear all, I have two questions regarding the weighting factors (0.265, 0.670, 0.065) that are used in the formula ( I = 0.265 IR+ 0.670 IG + 0.065 IB) with which one can convert the spectral irradiance triad to irradi…

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## [Validity of daylight factor results](https://discourse.radiance-online.org/t/validity-of-daylight-factor-results/6974)

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**Author:** [@Vin](https://discourse.radiance-online.org/u/Vin)\
**Replies:** 7\
**Last updated:** [March 17, 2026, 1:19am UTC](https://discourse.radiance-online.org/t/validity-of-daylight-factor-results/6974 "2026-03-17T01:19:41Z")

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Is it valid to average pixel daylight factor % across a .hdr image that has had pfilt x/2 y/2 applied to it? Or must the results be extracted from the source hdr before this transformation occurs?

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## [Faster Radiance on Windows](https://discourse.radiance-online.org/t/faster-radiance-on-windows/6957)

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**Author:** [@Taoning\_Wang1](https://discourse.radiance-online.org/u/Taoning_Wang1)\
**Replies:** 7\
**Last updated:** [March 13, 2026, 1:59am UTC](https://discourse.radiance-online.org/t/faster-radiance-on-windows/6957 "2026-03-13T01:59:53Z")

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Latest release include has some important updates for Windows users: Experimental multi-processing rcontrib: now rcontrib can be run with -n \> 1. It’s a workaround for the lack of fork() on Windows. Do expect larger m…

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## [Automated head install script](https://discourse.radiance-online.org/t/automated-head-install-script/369)

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**Author:** [@Andrew\_McNeil2](https://discourse.radiance-online.org/u/Andrew_McNeil2)\
**Replies:** 1\
**Last updated:** [February 26, 2026, 9:20pm UTC](https://discourse.radiance-online.org/t/automated-head-install-script/369 "2026-02-26T21:20:29Z")

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Hi Everyone, Since I download and compile the HEAD a lot, I wrote a script that automates it for me. It might not work for everyone as is, but it should be easy to modify the script to do what you want. The script c…

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## [Radiance 6 spectral materials now on spectraldb.com](https://discourse.radiance-online.org/t/radiance-6-spectral-materials-now-on-spectraldb-com/6965)

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**Author:** [@J\_Alstan\_Jakubiec](https://discourse.radiance-online.org/u/J_Alstan_Jakubiec)\
**Replies:** 1\
**Last updated:** [February 23, 2026, 7:10pm UTC](https://discourse.radiance-online.org/t/radiance-6-spectral-materials-now-on-spectraldb-com/6965 "2026-02-23T19:10:59Z")

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Hi all, Thanks to some very kind work by Greg, the Spectral Materials Database now has Radiance 6 spectral definitions for every material. For example, Thanks @Greg\_Ward! (PS. You mailed me just as the website hosti…

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## [Managing Radiance X Windows on Windows (WSL2 + VcXsrv)](https://discourse.radiance-online.org/t/managing-radiance-x-windows-on-windows-wsl2-vcxsrv/6964)

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**Author:** [@ephillips](https://discourse.radiance-online.org/u/ephillips)\
**Replies:** 0\
**Last updated:** [February 22, 2026, 5:46pm UTC](https://discourse.radiance-online.org/t/managing-radiance-x-windows-on-windows-wsl2-vcxsrv/6964 "2026-02-22T17:46:11Z")

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Managing Radiance X Windows on Windows (WSL2 + VcXsrv) Many Radiance tools (rview, ximage, objview, etc.) open X11 windows. Under Windows + WSL2, those windows can: Open oversized\\ Appear off-screen\\ Ignore geometr…

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## [Question about spectral output of rfluxmtx](https://discourse.radiance-online.org/t/question-about-spectral-output-of-rfluxmtx/6958)

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**Author:** [@Olivier](https://discourse.radiance-online.org/u/Olivier)\
**Replies:** 5\
**Last updated:** [February 20, 2026, 4:08pm UTC](https://discourse.radiance-online.org/t/question-about-spectral-output-of-rfluxmtx/6958 "2026-02-20T16:08:17Z")

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Hello everyone I am currently experimenting with the usage of the hyperspectral output of Radiance. When running rfluxmtx command I get the following header output in the .mtx file #?RADIANCE oconv -f -i ./radiance\_tmp…

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## [How to convert Melanopic illuminance to EMl or m-EDI](https://discourse.radiance-online.org/t/how-to-convert-melanopic-illuminance-to-eml-or-m-edi/6960)

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**Author:** [@soushiyant](https://discourse.radiance-online.org/u/soushiyant)\
**Replies:** 1\
**Last updated:** [February 6, 2026, 6:51pm UTC](https://discourse.radiance-online.org/t/how-to-convert-melanopic-illuminance-to-eml-or-m-edi/6960 "2026-02-06T18:51:10Z")

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Hello everyone, Based on my understanding, the output unit of rtrace with the -pM option and rcomb with the -c M option is melanopic illuminance (mev) in lux. I am trying to understand how this value is calculated in th…

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## [Rendering with rtpict with high number of processors](https://discourse.radiance-online.org/t/rendering-with-rtpict-with-high-number-of-processors/6954)

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**Author:** [@Vin](https://discourse.radiance-online.org/u/Vin)\
**Replies:** 3\
**Last updated:** [February 5, 2026, 11:53pm UTC](https://discourse.radiance-online.org/t/rendering-with-rtpict-with-high-number-of-processors/6954 "2026-02-05T23:53:18Z")

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I am attempting to run the below rtpict command on a google cloud VM instance with 192 CPUs. The command successfully runs. The problem I’m running into is that the max number of parallel process I can observe is 64. rt…

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## [Appropriate colours for gensky](https://discourse.radiance-online.org/t/appropriate-colours-for-gensky/6951)

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**Author:** [@Dion\_Moult](https://discourse.radiance-online.org/u/Dion_Moult)\
**Replies:** 10\
**Last updated:** [February 2, 2026, 7:57pm UTC](https://discourse.radiance-online.org/t/appropriate-colours-for-gensky/6951 "2026-02-02T19:57:48Z")

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G’day everyone! It’s been a long hiatus since I’ve touched Radiance, but I’m thrilled to see the community so active! I’ve recently been curious about Blender’s recently implemented multiple scattering sky texture, and c…

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