"Cross Flow Fan" marked the first feature number (numbers) within the meaning of the degree of protection: 0 No protection of persons or things outside without special protection. 1, to prevent more than 50mm of solid objects to prevent human intrusion (eg palm) accidentally come into contact with the parts inside the lamp. Prevent a larger size (diameter greater than 50mm) intrusion of foreign objects. 2, to prevent the intrusion of solid objects larger than 12mm of finger contact to prevent people inside the lamp to prevent parts of medium size (diameter 12mm) intrusion of foreign objects. 3, to prevent the intrusion of solid objects greater than 2.5mm in diameter or thickness greater than 2.5mm to prevent tools, wires or similar small details come into contact with foreign material intrusion inside the lamp parts. 4, to prevent the intrusion of solid objects greater than 1.0mm in diameter or thickness greater than 1.0mm to prevent tools, wires or similar small details come into contact with foreign material intrusion inside the lamp parts. 5, dust completely prevent intrusion of foreign material, though not completely prevent dust from entering, but the amount of dust intrusion does not affect the normal operation of the lamp. 6, dust to completely prevent the intrusion of foreign objects, and can completely prevent dust from entering.