**6. Conclusions**

Architectural and building science tries to gather and apply available human knowledge for the complex, aesthetic and functional creation of sophisticated habitable and healthy spaces with best environmental qualities encompassing shelter for human live, relaxation and work activities. Of course, the urban and structural objects with different interior spaces in their architectural plans and building forms have to respect natural conditions in various geographical locations, topography, local life stile and culture with trials for optimal solutions according to requirements concerning human health and prosperity, investor tendencies, investment and maintenance costs. To satisfy a complex sum of conditions, needs, codes and standards summarised by inhabitants, investors and national institutions leads to relatively simple and realistic criteria with a reasonable and experience-based background including simplified scientifically sound knowledge.

In case of utilising insolation and daylight conditions the traditional daylight science and technology is facing novel approaches and more real enhancements. In this sense are questionable also some older daylight criteria that were still recently used since the first calculation simplifications derived in the 18th Century. The Daylight Factor, Sky factor and Sky Component of the Daylight Factor used as basic criteria in various standards assume the existence of the unit uniform sky luminance after Lambert (1760). Although such Lambert uniform skies exist world-wide these do not represent typical sky luminance patterns in any site-specific conditions especially in subtropical, tropical and equatorial regions where mostly clear sky luminance distributions prevail that cause skylight illuminance conditions added frequently by sunlight.

This study tries to show and document that site-dependent daylight illuminance levels and their changes have to be expected in short-term, half-day, monthly or yearly variations in a realistic range under four typical half-daily situations. These situations can be classified with respect to relevant parameters which are dependent on extraterrestrially available illuminance reduced by atmospheric optical depth and air mass, turbidity and cloudiness conditions in site-specific variability. For practical purposes the probability of occurrence frequency of a particular half-day situation is related to the half-day or monthly relative sunshine duration which in absence of special measurements is available from many meteorological records world-wide. These monthly relative sunshine duration data can serve to estimate the local number of morning and afternoon half-day situations in any month and model their year-round expectance. Following this aim all data and figures after Bratislava and Athens CIE IDMP regular measurements can be considered as examples documenting the parameterisation and applicability of the four half-day situation system.

Current saving energy policies are also directed towards utilising renewable energy and in this respect also daylighting can serve to reduce electricity consumption in artificial illumination of interiors. A more precise determination of half-day illumination levels within year–round balance of supplementary electric lighting will enable to control it more effectively. Thus, daylight as natural source can be applied for interior illumination respecting local sunlight and skylight availability.
