We have investigated the dynamics of spontaneous emission from dye molecules embedded in opal photonic crystals. Fluorescence lifetimes of Rhodamine 6G (R6G) dye were measured as a function of both optical frequency and crystal lattice parameter of the polystyrene opals. Due to the broad homogeneous line width of the dye, the observed fluorescence lifetime varies only slightly with the frequency within the dye emission spectrum. The lifetime however does change as a function of the crystal lattice parameter. Our observations agree with theoretical calculations of the local density of optical states (LDOS) in the three-dimensional photonic crystals. The experiments and theory taken together reveal that the emission lifetime is modified over frequency ranges that are broader than the homogeneous emission line width of R6G dye.