A yellow-emitting ${\mathrm{Tb}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}:{\mathrm{Ce}}^{3+}$ (TAG:Ce) phosphor was coated on blue light-emitting diodes (LEDs) to obtain white LEDs (WLEDs). Since TAG:Ce showed 90% of the brightness of ${\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}:{\mathrm{Ce}}^{3+}$ (YAG:Ce), it was expected that TAG:Ce-based WLEDs showed 90% of brightness of YAG:Ce-based ones. However, the TAG:Ce-based WLED showed 74% of the brightness of YAG:Ce-based one. Considering the density and size of the phosphors, the higher density and larger size of TAG:Ce induced a great deal of sedimentation of TAG:Ce particles in an epoxy resin. It is believed that this is one of main reasons for the reduced optical power of the TAG:Ce-based WLED compared to that of the WLED expected from the brightness of TAG:Ce.