ok here's an example.
Say that your lamp has ID 58834.
Just do the following:
1) Add a trigger with these specs. (leave everything else as it is on the trigger)
Axis a: 10000
Axis b: 10000
Activation: anyone
On Activation: (object 58834) switchlight "ON"
That way the trigger is big enough to cover the entire map, and the "Activation: Anyone" tells you that any player/AI in the game will trigger the trigger ("activate it")
The "On Activation:" field tells you what will happen when the trigger is activated (when someones enters the triggers area). This will happen automatically because the trigger covers the entire map.
So, this little example will turn on the lamp, and it will always be on. I suppose you can change the On Activation: (object 58834) switchlight "ON" to "AUTO" instead, and that way it will turn itself on when the time is right (when darkness comes crawling).
Another way to do it is this:
1) On your players INIT field, place this:
On Activation: (object 58834) switchlight "ON"
The AUTO instead of ON works on this one as well.
The nice thing about the first way (the trigger way) is that you can choose when the light will go on. If you make the trigger, say 20x20, and place it near a house. The light (let's say that the street light is next to the house) will turn on when you go near the house.
I hoped this helped.