Watch the Sky HDR output units?

grasshopper honeybee-legacy
,
1

Hi,

i am trying to visualize false-color images of different skies, showing cd/m2, for educational reasons.
The WatchtheSky component is just perfect for this.
I noticed it writes 3 different HDR files whose names end in:
skyView.HDR
skyview_f.HDR
skyView_h.HDR

I was wondering about the following:

1.Is there a difference in units between the three?
2.How can i output a falsecolor showing cd/m2 ?
3.Is it the same units when producing the sky file with the genStandardCIESky (Radiance gensky) and the genClimateBasedSky (Radiance gendaylit) ?

2

Hi @IasonBournas,

The first file that you get is the output from Radiance rpict. This is the very bright, white image that you will get as a result. Human sensitivity is then applied to the HDR image to get a represenation of the human eye response, which gives you an image that you can visualize.
Last, the “_f” file is just a horizontal flip of the image to make the sky look as if seen from above.

The easiest way to output the falsecolor would be to run Honeybee_Falsecolor and use the first HDR image as an _HDRFilePath.

check this video from Mostapha with a nice explanation of the different skie types and their use

3

Hi Byron,

thank you for your response,

I was wondering about units in particular,
i have already generated false color images, but it seems the units are not cd/m²,
that is why is was asking.

4

It depends on the analysis type you choose to calculate: Luminance (cd/m2), Illuminance (lux) or Radiation (Wh/m2 or kWh/m2).
-A.

5

I used the script attached, but i can’t seem to find a choice between units,
SkyTypes.gh (492.0 KB)
i might be missing something

6

Ok i think i found it,
the HDR file ending skyView.HDR must be in W/sr/m2 (rpict result, -i boolean for radiance)
so this HDR must be connected to the falsecolor component,
and then from the falsecolor component you can multiply with 179 ( luminous efficacy, by default is 179 lm/W)
to get results in cd/m2.
If anyone knows please validate for future reference.