code optimisation - stuck.

Yes you can do that as long as LOW and HIGH are defined as 0 and 1. More generally though, they are not, so this form can be used:

       CS.digitalWrite(1, (Light_status == 0) ? LOW : HIGH);

Also you can simplify your arithmetic to

     Light_status = (++Light_status) % 2;

You last return statement also does not return anything.