How to set HIGH or LOW to a variable

I am trying to pass HIGH or LOW to my function, but I am unsure of what datatype to use for it, can anyone tell me? I know it is boolean 0x1 and 0x0, but what is the smallest datatype that I can set these to?

writeAllLights(HIGH)
char writeAllLights( [type] _state) {
    //turn on all lights
}

byte