A lamp assembly for a flashlight device is provided, which contains a lamp member, at least an optical lens, and a rim member. The lamp member has a lamp housed in a closed casing with a transparent lens at an end of the closed casing. Around and at the outer side of the transparent lens, the lamp member has a flanged rim with a number of L-shaped notches configured around the inside circumference of the flanged rim. Correspondingly, the rim member has a number of wedges protruding from the outside circumference of the rim member. The rim member is joined to the flanged rim by making the wedges slide into the L-shaped notches, and the optical lens is thereby fixed between the rim member and the transparent lens.