LBT 1.3.0 - Direct and diffuse radiation

Hi all. I’m working with the new LBT 1.3.0 version and I’m trying to evaluate the solar radiation. Instead of LBT 1.2.0, in 1.3.0 there is no component that splits the direct and total radiation (direct + diffuse). I wonder if there is a method to visualize diffuse radiation. Any suggestions?


I modified the SkyMatrix component with custom direct normal radiation and evaluated the solar radiation with LB Incident Radiation.

The new direct normal radiation is a series of 8760 values made with all zeros. Can it also work for HB?

Hi @nicmancio ,

That’s definitely they way to create a sky with only diffuse radiation. If you’re talking about visualizing direct vs diffuse components of the sky dome, the show_comp_ input of the LB Sky Dome can show you the direct and diffuse components.

Thank you @chris ,

I’m referring to the old component of HB Radiance where there was total and direct radiation.


With the HB workflow, to evaluate Annual Irradiance, I need to create a custom diffuse (or direct) radiation EPW for the Wea component. Correct?

Hi @nicmancio ,

Can I ask what use case you need the direct irradiance for?

If it’s common enough, we can add the direct output back to the HB Annual Irradiance recipe. It still exists under the hood and you’ll see that there’s still a result folder for the direct results that’s next to the total:


I just didn’t expose it on the recipe because the component outputs were clearer without it and it seemed like something that was only helpful for a few narrow use cases (eg. comfort mapping with the SolarCal model). If I’m wrong, I’m happy to add it back.

Hi @chris.

I am understanding how and when solar radiation is positive throughout the year on the facade. To understand this, I have to divide the direct and diffuse radiation, and taking into account the external temperature as a parameter, understand when the radiation is positive. For example, when the external temperature is lower than 16 °C I consider the contribution of both direct and diffuse radiation to be positive, when the external temperature is higher I consider only diffuse radiation to be positive. This to find a good compromise between heat gain and daylight.

Hi @nicmancio ,

I’m sorry that I still don’t understand why you only want to consider diffuse irradiance when the outdoor temperature is above a certain value but you can just connect up the path to that “direct” folder that the recipe produces to any of the Annual Result parsing components that you see in the HB-Radiance tab. Then, you’ll get the values for just the direct contribution and you can compare this to the total output that already comes from the component.

Hi @chris,

considering the internal comfort, during the summer, I have to minimize direct radiation to reduce internal solar gain. To do this, I have to understand how and where to put the windows and the shading systems. However, I have to find a balance between internal heat load and daylight for the comfort of natural light. On the other hand, during the winter, spring and autumn both the radiation (direct and diffuse) make a positive contribution both to the thermal load and to the daylight. But the seasons are different depending on the location and for this reason I have chosen the temperature as a parameter.

I have an exercise that uses Galapagos to maximize diffuse radiation and minimize direct radiation. For that, I used the old GenCumulativeSkiMtx and the 2 SelectSkyMtx, one for the diffuse and one for the direct.

I tried to reproduce the strategy proposed here, but the sum of diffuse and the direct radiation didn’t equal the full radiation.

Am I missing something?

Hi @chris and @nicmancio,

I’ve been doing something similar. I am trying to understand how much heat goes trough a windows (given the building geometry and context) and decompose it to its diffuse and direct components.

I’ve used the same trick to nullify either the diffuse or direct values from the .epw file.

  • When I sum up back the results I got a 4% relative error with the full simulation (direct+diffuse). Is this normal to you ?

  • My .EPW file is in Lyon, middle of France. The diffuse part is about 55% of the total heat gain, cumulated over the year. I am not really used to Radiance modelling : does it looks credible to you ? I would have guessed something much lower for the diffuse part. Maybe my intuition is not good.

  • I’ve also compared LB and HB and find a 4% relative error : is it the normal deviation I should expect between these tools for the same analysis ? (127.8 KB)

Hey @lionpeloux ,

This post explains why zeroing out the direct or diffuse sky isn’t giving you what you expect:

Oh great. Thank you @chris.
This is much clear to me now.