Dears.
i am just a beginer........
My requirement is to lit 6/8 LED of 1W (700mA) in 230 V ac power. what is the most efficent circuit. i read about heating trouble in linear circuit. so please help me.
There are a number of ways to do it. One way is to step the 230VAC voltage down to something that can be rectified and filtered (and perhaps regulated) to DC voltage just large enough to power the LEDs appropriately. That can be done linearly with good efficiency. Another way is to use a switch-mode converter to leverage feedback to optimize the efficiency -- but that is quite a bit more complicated.