can someone help. Im having a hard time making sketch for sleep mode in my arduino uno. I dont understand tutorials in youtube. I really need the code for it. the triggering device is the light dependet resistor, the function will be; if night the arduino will be in sleep mode. thanks in advance for your help guys 
Have a read (rather than a look at videos) to Nick's blog
Understand what's written there, then post your best attempt at commented code. (Within code tags)