This paper analyses the forecast accuracy of current state-of-the-art, data-driven, spectral sky models. The aim is threefold: (i) to determine the forecast accuracy of existing spectral sky models based on a large dataset of spatially, spectrally and temporally resolved measurements, (ii) to investigate the practical implications of spectral forecast accuracies for the assessment of spectrally selective responses (here non-image-forming effects are expressed through melanopic irradiance) and (iii) to study if the use of spectral sky models is more appropriate to predict the non-image-forming effectiveness of daylight than the currently assumed CIE standard illuminant D65. The forecast analysis for CIE Standard Overcast Skies (CIE Sky Type 3) showed that the model published by Chain and colleagues in 1999 performed best, whereas the correlated colour temperature distribution can also be represented with the CIE standard illuminant D65. The analysis showed substantial discrepancies in the forecast for clear skies with low luminance turbidity (CIE Sky Type 12) depending on the correlated colour temperature range. Our findings suggest that for CIE 12 skies, even when simulating with the best performing spectral sky model, forecast inaccuracies affect the estimated non-image-forming effectiveness. Nonetheless, the assumption that the spectral distribution of daylight from a CIE 12 sky corresponds with the CIE standard illuminant D65 underestimates the non-image-forming effectiveness to a greater extent. The results advance the understanding of spectral characteristics of daylight and suggest that considering realistic spectral distributions instead of D65 will lead to a difference in the non-image-forming effectiveness assessment.

本文分析了当前最新的，数据驱动的光谱天空模型的预测准确性。目的是三方面的：（i）基于空间，光谱和时间分辨测量的大型数据集，确定现有光谱天空模型的预测准确性，（ii）研究光谱预测准确性对评估光谱选择性的实际意义响应（此处非成像效果通过黑素辐射表示）和（iii）研究使用光谱天空模型是否比当前假定的CIE标准光源D65更适合于预测日光的非成像效果。对CIE标准阴天（CIE Sky Type 3）的预测分析表明，Chain及其同事在1999年发布的模型效果最好，相关色温分布也可以用CIE标准光源D65表示。分析表明，根据相关色温范围，低亮度浊度晴朗的天空（CIE Sky Type 12）的预报存在很大差异。我们的发现表明，对于CIE 12的天空，即使使用性能最佳的光谱天空模型进行模拟，预测的不准确性也会影响估计的非成像效果。但是，来自CIE 12天空的日光光谱分布与CIE标准光源D65相对应的假设在很大程度上低估了非成像效果。