Against the law?

ok so i wanna know for sure if led taillights are against the law or not. is there a limit on how big they have to be? and what about not having any side markers in the back? i have been told by a bunch of old people that they cant be legal because they arent wraped around the side so that they can be seen from the side. i have 2 flush mounted 10" leds in the top of my tailgate(pics coming soon), and they are up far enough to see when people are riding my ass. and bright enough that it makes there grill shine red through there high beams.