LED lamp having a sealed structure

An LED lamp comprising:

• a heat sink having a cylinder, a plurality of connecting arms extending outwardly from the cylinder and a plurality of fins extending from each of the arms;
• a plurality LED modules each mounted on an outer surface of an outermost one of the plurality of fins;
• a lamp holder secured to a bottom of the heat sink adapted for connecting with a supporting rod for fixing the LED lamp in position, the lamp holder having an annular inner flange and an annular outer flange and a groove between the inner and outer flanges, the outer flange defining a plurality of cutouts therein adapted for facilitating flowing out of water in the groove;
• a waterproof cushion received in the groove;
• an envelope surrounding the heat sink and the LED modules, having a bottom end fitted into the groove;
• a cover mounted to top ends of the heat sink and the envelope, wherein the cover is thermally connected with the heat sink and heat absorbed by the heat sink from the LED modules is dissipated to surrounding air of the LED lamp through the cover.