An LED lamp has a base, an LED device and a convex lens. The base has a recess. The LED device is mounted in the recess and has an LED. The convex lens is mounted in the recess, separates from the LED and has a cavity formed in the convex lens. The cavity has a bottom, an opening, an inner side surface and an imaging surface. Peripheries of the bottom and the opening of the cavity are wavy. The imaging surface is formed around the inner side surface, inclines from the bottom to the opening of the cavity and is wavy. The imaging surface is capable of refracting light emitted from the single one LED located in the cavity to form a characteristic visual effect like a chrysanthemum.