Simulating light tubes using the three phase method

three-phase
light-tube

#1

Hey,
I tried to use the three phase example file to simulate light tubes, but it did not give any changes in the results. I tried many things, such as having the collector at the top as a honeybee window surface, and removing it at all so I only have the diffuser at the bottom with a BSDF. Any suggestions of what could be the problem? I could not attach the file that I used.

In this case, is it better to use the daylight coefficient method? because I tried it and it gave me an error after the simulation related to the input data that I used. Can you use BSDF materials in the daylight coefficient method?

Thanks in advance.


#2

Hi Maha,

Not exactly answering to your questions but in a similar problem I used the photon mapping method [mkpmap] (forward raytracing). You can find information here and here.

It needs some time to understand the physics and fiddle a bit around with parameters to get results but it works well for light tubes and light redirecting materials. Below is an example for a light redirecting profile I had to assess. BSDF materials work well with this method.

Maybe it is worth having a look at it.


BSDF material_light pipe
#3

Modeling a light-pipe is a special case of using 3 phase which is not possible to recreate with the current built-in recipes in the Grasshopper plugin. Andy has a great tutorial which shows the workflow for modeling a light-pipe in 3 phase (see page 92). The step that you need to add to the workflow is the light-pipe transmission (page 105) which both the receiver and the sender are geometries.

Not to say that you can use Honeybee[+] library and recreate Andy’s workflow. @sarith did tested Honeybee[+] for modeling light pipes successfully but we never considered that to be a recipe for the plugins.


#4

A proper equivalent for the Three Phase Method for light tubes, assuming that their interior is specular, will be Out-of-Core Photon Mapping:
http://www.tandfonline.com/doi/full/10.1080/19401493.2016.1177116
https://www.radiance-online.org/community/workshops/2016-padua/presentations/104-BauerSchregle-oocpmap.pdf

Unfortunately, OOC isn’t implemented for Windows right now (at least in the official NREL release): https://github.com/NREL/Radiance/commit/edf7c6ff9af7642ca3853e28894413cefb876695


#5

Hi Sarith,

Do you have a happen to have a test file containing the geometry for a light pipe? I can test it using OOC pmap over the weekend and post some results here…


#6

I think I was using the same files that Mostapha had sent me. The gh file should be somewhere on the github page. I usually do Photon Mapping examples with Sketchup and su2rad.


#7

Okay. Interesting. I have a workflow that uses HB to generate the necessary RAD files and then some custom python GH components that prepares the sim for running pmap on a linux machine. Have never tried the Sketchup + su2rad approach… I’ll try to work out an example for light pipes with pmap for the community


#8

Hey everyone,
thanks alot for your replies. I am interested in applying honeybee plus since I only use windows. @mostapha thanks I will check the tutorial by Andy, and will post if I have any questions.
@sarith do you have test using Honeybee plus for modelling light pipes?


#9

Hey @mostapha
so sorry for bothering again, I now realize that it is hard to make the workflow from andy using honeybee plus… I understand the problem more now…Do you have the test that Sarith did? or can you guide me more into how to do it?


#10

I am not sure if Three Phase Method is the right approach for these kind of problems. I tried a few ambient settings and found that not enough light gets in :


The simulation in the lowest row is with 9 ambient bounces.

F-Matrix is probably the way to go:

I don’t foresee myself implementing the F-Matrix (aka 4 phase method) in HB[+] anytime soon. However, if somebody with understanding of Python and Radiance is willing to implement this in the HB[+] API, both @mostapha and I might be able to provide some guidance.

Sarith

PS: I can’t share all the files used in the above simulations, but if somebody is interested in the commands, here they are: https://gist.github.com/sariths/f36e458dd06ef5658f18172ddb143df8

PS: PS: The simulations shown in the first video can be done on HB+ , just use the recipe for Image-based daylight coefficients.


#11

Hey Sarith,
thanks alot for taking the time to respond… I dont think I will be able to do that now, but I will let you and @mostapha know if I test it in the future.

Thanks again,


#12

Hey Sarith,
I have seen an tutorial that using daylight coefficients method to calculate the output lumen of the light tubes at a specified situation, the formula is as followed


and the DC value of light tubes for sky patches and for sun have been calculated by matlab.
May I use the calculated DCs to modified the existed DCs gengrated in annual daylight simulation, and then get the new annual result, which is the simulated light tubes application results?


#13

Hi Zhang,

How does the DC calculated by Matlab for the light tube work? Is it using a combination of Monte Carlo methods and ambient caching?
You might (can’t say for sure) be able to get the DC recipe in HB[+] to work by running the simulations to convergence. Just keep increasing the values of -ab and -ad (while decreasing -lw as 1/ad) till you get convergence. For testing convergence, you can measure the MSE between two consecutive resultant illuminance grids.