Daylight Simulating Mirror Material for Light pipe



Hi All,

I am trying to run a point in time illuminance analysis and I want to see the effect of a highly reflective light pipe. I am not able to apply the reflectivity of 98% to the light pipe. I have checked the normal direction of the surface.

I am sure I am doing something wrong.


I set the highest radiance parameters based on this site.
Any help would be highly appreciated. (763.9 KB)


I have tried to set the number for ambient bounce very high. Still the results don’t change at all.


Hi @devang, I´m sure @sarith will be able to answer better, but in general you can´t run light pipe simulation cause of the sky and many other issues. There are 2 things you can try, 1) photonmapping 2) 3/5 phase method , have a look here from page 92 .
@mostapha have done it so you can ask him for the files, probably they were shared on the forum some time ago



Yeah @mostapha did this back in 2014. So far there’s only this tweet @mostapha can you cook an example please?


+1 to what @PeterZatko said. Photon mapping, ironically, is the most straightforward approach for this. You can get that done by directing the photons to the mouth of the pipe using a photon-port (the photon map manual). @mostapha and I started a dialog with the lead researchers of Photon Mapping to implement this in HB[+], but it will be a while before it all falls into place.

The other point-in-time approach using rpict might require you to run genBSDF first to encapsulate the diffuse part of the calculations in a separate XML data structure and then use BSDFs “in-scene” (see this and this).

The phase(matrix)-based approach is somewhat complicated. It is also probably the most inaccurate as we dont do much by the way of specular calculations in Three-Phase or Five-Phase. Last I checked there were no empirical validations for this approach (within this context). In case you want to give it a shot, here is a demo of what worked for me the last time I tried. The images on the bottom are from a four-phase simulation (on the left is DC).

The matrix order for tracing rays is something like shown in this script: . If you use Andy’s approach from the presentation that Peter shared, remember to use the “light” primitive as recommended by him on page 96 (in HB[+] all matrix calculations are currently Monte-Carlo based and therefore employ glow instead of light) .


Thanks a lot @sarith and @PeterZatko,

I will need to take a look at the resources you shared. Hope to acquire necessary knowledge of radiance to simulate this in future.


@devang how good are you in hardcore radiance ? cause, If you have a linux system (nowdays also probably running on Windows), than you can create your geometry in HB legacy and wite extra line for the Photonport see the Photonmapping manual @sarith shared and tun the simulation from comandline as per manual. I tried that way once and it´s fine, you can even read back the results via HB legacy. So I suggest you to follow the photonmapping manual, as nowadays that´s the easiest way, at least for me


I am far away from that unfortunately. But I will take this opportunity to enter a new territory. :neutral_face:
Thanks a lot!


This questions proved an important principle of the universe for me. “What you think you should know, eventually you have to know.”


Hi @devang, I will share the folder with you which I received form Andy. I couldn’t find the definition that I create in Grasshopper. That should be a good starting point. I would replace the window material with a black material, run the light-pipe simulation separately, and then add them up.

Also I’m refactoring the Honeybee[+] API to make cases like this more accessible and easier to do. Will keep you posted on that.