Though numerous daylight studies have been conducted worldwide, works for the daylight climate and/or the daylight variations/trends are rare. This gap is treated here. Therefore, the innovative trend analysis and the month–hour diagrams are applied to the illuminance time series at Athens over the period of 1992–2017 under all-/clear-sky conditions. For all skies, the global illuminance shows a broad maximum at summer noon, while the diffuse counterpart is in spring. Under clear skies, the global illuminance maximum becomes broader, covering spring/summer. However, the diffuse illuminance maximum splits into minor ones in April and June. The innovative trend analysis method finds that the identified trends are + 2.83%/decade (−1.89%/decade) for the global (diffuse) illuminance, under all skies. In clear skies, the above values are modified to +2.66%/decade (−2.00%/decade). These results confirm a recovery in the Athens daylight levels as in the solar radiation ones found by many researchers. Another outcome of the study concerns the observed decline in diffuse illuminance levels in the examined period, which may be attributed to a decline in cloudiness and an increase of sunshine over the area. Also, the variation of the global and diffuse illuminance efficacies on a month–hour basis is examined using the month–hour diagram method.

中文翻译：

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雅典的日光气候：1992-2017 年期间的变化和趋势，亮化时代

尽管在世界范围内进行了大量日光研究，但针对日光气候和/或日光变化/趋势的研究很少见。此处处理此间隙。因此，创新的趋势分析和月-小时图应用于雅典 1992-2017 年全天/晴天条件下的照度时间序列。对于所有天空，全球照度在夏季中午显示出广泛的最大值，而漫射对应在春季。在晴朗的天空下，全球最大照度变得更广，涵盖春夏两季。然而，漫射照度最大值在四月和六月分裂成次要的。创新的趋势分析方法发现，对于所有天空下的全球（漫射）照度，识别的趋势为 + 2.83%/十年（-1.89%/十年）。在晴朗的天空中，上述值修改为+2。66%/十年（-2.00%/十年）。这些结果证实了雅典日光水平的恢复，就像许多研究人员发现的太阳辐射水平一样。研究的另一个结果涉及在检查期间观察到的漫射照度水平下降，这可能归因于该地区的云量减少和日照增加。此外，还使用月-小时图方法检查了以月-小时为基础的全局和漫射照度功效的变化。