honeybee_radiance.lightsource.sky.certainirradiance module

Generate sky with certain irradiance.

class honeybee_radiance.lightsource.sky.certainirradiance.CertainIrradiance(irradiance=558.659, ground_reflectance=0.2, uniform=False)[source]

Bases: honeybee_radiance.lightsource.sky._skybase._PointInTime

sky with certain irradiance.

The output of CertainIrradiance sky is similar to using command below:

gensky -c -B desired_irradiance

You can also generate the sky with certain illuminance using from_illuminance classmethod. The method converts the illuminance value to irradiance by dividing it by 179.0:

gensky -c -B [desired_illuminance / 179.0]

It also includes ground glow source. Ground reflectance is set to %20 by default which is gensky’s default value. Use ground_reflectance property to adjust this value.


The conversion factor in the Radiance system for luminous efficacy is fixed at KR= 179 lumens/watt (lm/w). This should not be confused with the more usual daylighting value, which can be anywhere between 50 and 150 lm/w depending on the type of sky or light considered.

For more information see links below on the Radiance forum:

Default value is set to 558.659 which corresponds to a sky with 100,000 lux horizontal illuminance.

  • irradiance – Desired horizontal diffuse irradiance value in watts/meter2 (Default: 558.659).

  • ground_reflectance – Average ground reflectance (Default: 0.2).

  • uniform – Boolean to note whether the sky is uniform instead of cloudy. (Default: False)

  • irradiance

  • illuminance

  • ground_hemisphere

  • sky_hemisphere

  • ground_reflectance

  • uniform

  • is_point_in_time

  • is_climate_based


Overwrite .NET ToString.

classmethod from_dict(data)[source]

Create the sky from a dictionary.


data – A python dictionary in the following format

    'type': 'CertainIrradiance',
    'irradiance': 558.659,
    'ground_reflectance': 0.2,
    'uniform': False
classmethod from_illuminance(illuminance=100000, ground_reflectance=0.2, uniform=False)[source]

Create sky with certain illuminance.

  • illuminance – Desired horizontal illuminance value in lux (Default: 100000).

  • ground_reflectance – Average ground reflectance (Default: 0.2).

  • uniform – Boolean to note whether the sky is uniform instead of cloudy. (Default: False)

classmethod from_string(sky_string)[source]

Create a CertainIrradiance sky from a string.


sky_string – A text string representing a CertainIrradiance sky. This can be either a string with a certain irradiance (eg. “irradiance 558.659”) or with a certain illuminance (eg. “illuminance 100000”). Any sky string can optionally have a “-g” property of a fractional number, which sets the reflectance of the ground. If unspecified, the ground will have a reflectance of 0.2. This sky can also have a “-u” property to set the sky as uniform instead of the default cloudy.


# irradiance string representation of the sky
sky_string = "irradiance 558.659"
sky = CertainIrradiance.from_string(sky_string)

# illuminance string representation of the sky
sky_string = "illuminance 100000 -g 0.3 -u"
sky = CertainIrradiance.from_string(sky_string)

Translate sky to a dictionary.

to_file(folder, name=None, mkdir=False)[source]

Write sky hemisphere to a sky_hemisphere.rad Radiance file.

  • folder – Target folder.

  • name – File name.

  • mkdir – A boolean to note if the directory should be created if doesn’t exist (default: False).


Full path to the newly created file.


Return radiance definition as a string.

property ground_hemisphere

Sky ground glow source.

property ground_reflectance

Get or set a value between 0 and 1 for the ground reflectance.

If not specified, a default of 0.2 will be used.

property illuminance

Sky illuminance value.

property irradiance

Sky irradiance value.

property is_climate_based

Return True if the sky is created based on values from weather data.

property is_point_in_time

Return True if the sky is generated for a single point in time.

property sky_hemisphere

Sky hemisphere glow source.

property uniform

Boolean to note whether the sky is uniform instead of cloudy.