Decorative Lamp

FIG. 1 is a front, right and top perspective view of a decorative lamp, showing my design. FIG. 2 is a rear, left and bottom perspective view thereof. FIG. 3 is a front elevation view thereof. FIG. 4 is a rear elevation view thereof. FIG. 5 is a left side elevation view thereof. FIG. 6 is a right side elevation view thereof. FIG. 7 is a top plan view thereof. FIG. 8 is a bottom plan view thereof. FIG. 9 is a front, right and top perspective view of the decorative lamp in a first configuration of use; and, FIG. 10 is a front, left and top perspective view of the decorative lamp in a second configuration of use. The broken lines depict portions of the decorative lamp that form no part of the claimed design. Environment of the decorative lamp in a first and second configuration of use is shown in FIGS. 9 and 10 and forms no part of the claimed design.