The present invention provides a lamp for lightweight steel frame, comprising: a first frame, containing a power supply module at the back, at least two heat sinks at both sides of the power supply module, and a conductor for electrical connection with the power supply module; at least a LED assembly mounted in front of the first frame; the LED assembly is electrically connected with the conductor to form a spotted light source; at least a reflector used to convert the spotted light source into directional beam for projection into external environment; the reflector is installed within the front of first frame; a second frame for the lightweight steel frame, defining a space for covering the first frame; two diffusers arranged between the reflector and substrate, as well as a condenser between the diffusers. With this design, the reflector could project the directional beam into intended external environment for improved power consumption, environmental protection and illuminance.