ำEqn (9.3) describes the re-absorption of rays outside the solid angle of the escape cone shown in figure 9.2(a), and is appropriate for rays which enter a solar cell of a higher refractive index than the collector. if we wish to describe the photon flux emitted from the edge of the collector--a useful characterisation technique, as well see in Section 9.4.2---a modification of Weber and Lambe's theory is required [Figure 9.2(b)] since only photons emitted in escape cone at edge can be collected by the detector