The article describes the analytical expression approximating experimental data on daily natural illuminance on the Earth surface with different types and conditions of cloud cover over the 11-year solar activity cycle within the solar altitude angle range of 0 ° to 90 °. The values of the direct, diffused, and total illuminance on the Earth surface with different types and conditions of the cloud cover and, to some extent, of the substrate were defined and summarised in tables. The data presented may be used as part of the visual perception studies, light and engineering calculations, architecture and construction practice, etc. 1. Glezer V.D. Sight and Thinking [Zreniye i myshleniye / Leningrad: Nauka, Leningrad Branch, 1985, 244 p.
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• Sun
• 11- year solar activity cycle
• solar altitude angle
• year number
• day of a year
• clouds
• Earth surface
• natural illuminance
• direct
• diffused
• and total illuminance