Experimental Validation of <i>Radiance</i>-Based Methods for Simulating Solar Penumbras and Pinhole Projections

The sun’s vast size creates two distinct shadow phenomena on Earth: solar penumbras and pinhole projections. These sunlight effects are particularly important in daylight perception research and exacting daylighting design. As such, a method to generate accurate and efficient lighting simulations of these sunlight effects is needed to facilitate research and design applications. The present study is the first to investigate the accuracy of three <i>Radiance</i>-based methods for generating solar penumbras and pinhole projections against real-world measurements using various semi-controlled scenarios. In addition, we examine the applicability of these methods in terms of simulation time and file size. These methods involve the use of <i>Radiance’s</i> direct jittering algorithm, utilizing solely <i>Radiance’s</i> stochastic calculation, and subdividing a <i>Radiance</i> sun into many small suns. The simulation results of solar penumbras and pinhole projections per method are compared to real-world measurement data and assessed on their applicability. The results show that employing a subdivided sun offers an accurate and efficient method for simulating scenes with solar penumbras and pinhole projections using <i>Radiance</i>.太阳的巨大体积会在地球表面产生两种截然不同的阴影现象：太阳半影（solar penumbras）与小孔成像投影（pinhole projections）。这类日光效应在日光感知研究与高精度采光设计领域具有重要价值，因此亟需能够精准高效模拟这类日光效应的方法，以支撑相关研究与设计应用的开展。本研究首次针对三种基于Radiance的太阳半影与小孔成像投影生成方法，通过多组半受控场景开展真实测量对比以验证其精度；同时从模拟耗时与文件体积两个维度，评估了上述方法的适用性。这三类方法分别为：采用Radiance的直接抖动算法、仅调用Radiance的随机计算功能，以及将Radiance模拟的太阳拆分为多个微型太阳。本研究将每种方法生成的太阳半影与小孔成像投影仿真结果与真实测量数据进行对比并评估适用性，结果显示，采用拆分式太阳模型的方法，是利用Radiance模拟太阳半影与小孔成像投影场景的精准高效方案。