Phosphor heat generation in phosphor-converted light-emitting diodes (pc-LEDs) plays an important role in affecting the optical and thermal performance of LEDs, but it is hard to measure directly. In this paper, we developed a method to calculate the phosphor heat generation by modifying the Kubelka-Munk theory. With full consideration of light scattering, absorption and conversion inside the phosphor layer simultaneously, we calculated the phosphor heat generation and analyzed its trend with changing the phosphor quantum efficiency and phosphor parameters (concentration, thickness, particle size). Experiments were also conducted to validate the calculations. It was found that with the increase of phosphor concentration from 0.11 to 034 g/cm(3), the total energy loss increases by 54.11%. The phosphor concentration and thickness played similar roles in affecting the phosphor heat generation. The maximum phosphor heat generation corresponded to the phosphor particle size of around 2 mu m, which is denoted as the critical size. (C) 2014 Elsevier Ltd. All rights reserved.