An LED lamp includes a bracket, two guiding plates and a number of LED assemblies. Each of the guiding plates includes a body, a top flange and a bottom flange extending from top and bottom edges of the body, respectively. The bottom flanges are mounted on opposite sides of the bracket. The top flanges are oriented towards each other. The LED assemblies are mounted to the bracket and sandwiched between the bodies of the guiding plates. The LED assemblies slide along a longitudinal direction of the guiding plates before the LED assemblies are assembled to the bracket by screwing the LED assemblies to the guiding plates. The quantity of the LED assemblies assembled to the bracket is selective thereby to meet different luminous density requirements/specifications.