24v ac coverted 12v dc for 30 watt LED
The LM7812CT provides 12 volts at up to 1 amp. That's a typical maximum continuous output power of 12 watts.


  I want run 30Watts LED


There's your first problem. A 7812 is inappropriate for that power level.

Your second problem is the 1 kohm resistor will not pass anything like enough current to make a powerful LED operate without burning.  Try something like this: -



You'll still need the bridge rectifier and reservoir capacitors but those capacitors will need to be hundreds of uF, possibly 1000 uF or more to get a reasonably smooth DC output voltage with an AC input frequency at only 50 Hz.