VSC daylight component

Hi there!

I noticed that there isn’t a Vertical Sky Component (VSC) component in the newest version of Ladybug and Honeybee (1.3.0). I was wondering if there is a new component (or script) that could substitute the VSC component in the recent version.

Also, I am trying to analyse a façade in terms of daylight (I am trying to use VSC as one of the metrics, together with sunlight hours). Has anyone come across with a different metric (maybe in terms of luxes) to analyse daylight in the facades of few buildings within a masterplan in an early stage of design?

Thanks in advance!

Hi @cheo081095 ,

We just called the component HB Sky View in the new LBT plugin. If you read the description, it tells you the following:

Note that computing cloudy Sky View for a vertically-oriented geometry (horizontal sensor direction) will yield Vertical Sky Component (VSC) as described by the UK Building Research Establishment (BRE).

The HB Annual Daylight recipe is a much more robust way to quantify daylight than VSC but it will take longer to run.

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Perfect! I will have a look at that. Many thanks @chris

I’m getting values of around 50% on my Sky View run.
I assume that the Sky View somehow doesn’t take into consideration the cossine law that limits the Vertical Sky Component to 39.xxx %.
Can this be corrected, maybe using the radiance parameters?

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I found that using the cloudy sky limited my results to 40 %.
Though I dont understand why :no_mouth:

@AlexanderLundmark ,

As I said above, you need to use a cloudy sky if you are using this component to compute VSC and not the fraction of the sky dome visible by the sensor.

As you can see, th cloudy sky is brighter on top than it is on the sides:

I tried today a VSC analysis, and the maximum value was higher than 40%, around 50%. The default option is with -ab 2, but VSC does not consider reflections. Although in this post it was reported that the results were around 40% when using the Overcast Sky.
Then I tried changing to -ab 0, either through the simple parameters in a GH panel, or through the Radiance parameter component in Honeybee. It did not reduce the result. I tried this also with the Sky View component and a Daylight Factor component. The Daylight Factor with -ab 0 does not seem to work.
Any thoughts? Thank you

Hey @arlind.dervishaj ,

It’s technically possible to get VSC greater than 50% if your sensors are not set up to be “vertical.” It seems likely that you might not have set up your sensors to be vertical and you are actually computing horizontal sky component instead of vertical sky component.

To get VSC, you should be plugging _directions_ into the HB Sensor Grid component, which align the surface used to generate the sensor points. If these surfaces are truly vertical (so that you’re computing vertical sky component), then the direction vectors that they generate should be parallel to the ground plane.

I hope that makes sense and, FYI, changing the -ab input to the Sky View recipe will have no effect because there is a hard-coded value for this embedded within the recipe logic. It has an effect on Daylight Factor since light bounces are relevant there but -ab 0 essentially means that you only care about the direct sun and not the overall sky illumination. So that’s obviously going to be zero when you’re computing daylight factor with a cloudy sky. You should set -ab 1 if you want to account for the sky dome illumination but not any bounces of light off of that illumination.

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Hi @chris,
Thank you so much for your reply. Yes, I was doing something wrong, probably I hadn´t connected the directions. Now the results on vertical surfaces for VSC are within 40% with the CIE overcast sky. Thank you also for the clarification on ambient bounces!

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@chris I have a follow up question that is more theoretical than LB/HB-component-specific … I hope that’s OK.

I’ve been trying to find literature on the history of VSC and use for it, since it seems to be an easy-to-calculate metric that is WWR agnostic and hence good for early design. I keep finding resources that say VSC >= 27% means ‘conventional window design’ will allow for good daylight, but I cannot find anything that indicates what conventional means. Is there an approximate WWR value that corresponds to ‘conventional’? 25%? 30%? 40%?

Thanks in advance!