AirBoundary not considered fully transparent by Radiance?

mikkel · July 17, 2021, 10:02am

Radiance uses transmissivity for the glass modifier. Usually we only know the transmittance, which is the _trans input. The formula is:

tn = (sqrt(0.8402528435 + 0.0072522239 * Tn * Tn) - 0.9166530661) / 0.0036261119 / Tn

tn = transmissivity
Tn = transmittance

That’s why 0.918 becomes 0.999654936013.

You can also see formula in this definition (get_transmissivity):

github.com

ladybug-tools/honeybee-radiance/blob/master/honeybee_radiance/modifier/material/glass.py#L343


      
          """Initialize Glass from a dictionary.
          
          Args:
              data: A dictionary in the format below.
          
          .. code-block:: python
          
              {
              "type": "Glass",
              "identifier": "",  # Material identifier
              "display_name": "",  # Material display name
              "r_transmissivity": float,  # Transmissivity for red
              "g_transmissivity": float,  # Transmissivity for green
              "b_transmissivity": float,  # Transmissivity for blue
              "refraction_index": float,  # Index of refraction
              "modifier": {},  # material modifier (Default: None)
              "dependencies": []
              }
          """
          cls._dict_type_check(cls.__name__, data)
          modifier, dependencies = cls.filter_dict_input(data)