A light assembly includes a fixing unit and a lighting unit located within a lamp cover. The fixing unit includes a substrate board with a recessed shape, and an elastic steel ring is engaged with the hook flange of the substrate board in order to increase the tightness between the substrate board and the lamp cover so as to prevent water vapor and salt mist from entering into the light assembly, and thereby the corrosion of light source and circuit can be avoided. The light emitting diode is used as a light source instead of the conventional halogen lamp.