how to simply turn on/off a rated LED Light ?????

Hi everyone ! i'm a newbie here having trouble turning on/off an LED pin Light having the ff. specs: -220VAC in, 28VDC out, 7watts i'm using an arduino uno controller and i don;t know what relay is suitable for driving this light, i am also confused because i saw in an article that a diode and an NPN transistor must be used to protect the arduino from damages ... care to help pls guys ??? tnx in advance !

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