Illuminance turbidity factor Til--Algorithm 1.21

The illuminance at the earth's surface from the solar beam depends on attenuation in the atmosphere; an index of this attenuation is the illuminance turbidity factor. The corresponding index of attenuation for total radiation is the Linke turbidity factor. More extensive data are available for Linke turbidity than illuminance turbidity, and this algorithm is an empirical conversimula.

Linke turbidity factor, TL

This equation gives the relationship between illuminance turbidity and Linke turbidity under European clear skies


Typical values of Til under cloudless skies are given in the following table:
region Til
perfectly dry clean air 1.0
dry mountain areas 1.5
rural areas 2.5
urban areas 3.0
industrial areas 5.0

  1. Page J K and Sharples S The SERC meteorological data base Volume II: algorithm manual 2nd Edition Department of Building Science University of Sheffield (1988)
  2. Page J K and Thompson J L Modelling daylight availability National Lighting Conference Warwick 1982 Chartered Institution of Building Services

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