The experimental and simulated optical efficiencies obtained using both the surface normal and enclosing shape methods in pvTrace v2.1.sv are shown in Figure . As seen, the enclosing shape method shows excellent agreement with experiment (Δ𝜂 !"# = 0.15 ± 0.10%). In contrast, the surface normal method yields efficiencies which significantly deviate from experiment (Δ𝜂 !"# = 6.49 ± 0.67%), and falsely predicts the trend in relative efficiency of each geometry. This discrepancy between the two methods is attributed to the experimental approach used to determine the efficiency, in which there is an air gap (~3 mm) between the LSC edge and the input port on the integrating sphere. The enclosing shape method better represents this configuration, whereas the surface normal method is more analogous to experimental determination using PV cells directly attached to the LSC edge (no air gap). The increased 𝜂 !"# obtained using the surface normal method may also indicate that the integrating sphere measurement underestimates the true photon efficiency, due to the introduction of optical artifacts at the air gap (e.g., increased scattering or refraction due to the change in refractive index leading to loss of photons from the optical path). )), a circle with a flat edge (4), and a regular circle (5) were used. Note that these differ from the designs in Figure due to their size. Solid ( ) and hollow cylindrical array (7) LSCs were also considered, along with a design LSC based on the Leaf Roof (8). Finally, original designs were used, including another leaf-like LSC ( ) and a vertically-oriented cylindrical array (10). These hypothetical LSCs were simulated with pvTrace-v2.1.sv using 100,000 rays parallelized over 64 cores, using a custom light mask for each design, as described in the Experimental. Figure shows the external photon efficiency calculated using both the surface normal and enclosing box methods. (bulk parts). Note the enclosing box method, not the enclosing shape method, to enable comparison between parts.