To be honest with you, there's not enough information here to calculate the answer, because we don't know the power consumption of the front porch light. The best we can do is represent that as a variable ... pick a catchy name for it, which will show up in the final answer, and then you can 'plug in' (get it ?) whatever size light bulb you want to use over the front porch.
OK. First we have to give it a name. I could use a single letter, but that's what everybody else always does. Remember ... this is going to represent the power (watts) consumed by the front porch light when it's turned on. It's the symbol that means "Front Porch Light Power" wherever you see it. I could easily call it x or y or z, but I'm going to call it " FPLP ".
OK. FPLP = power consumption of the light, in watts .
0.001 FPLP = power consumption of the light, in kilowatts (kW).