Disable directional light with trigger

Could someone please tell me how to turn off the directional light (or turn intensity to 0 and back) when hitting a box (or sphere) collider (or something else?). I searched the internet but for a noob like me I'm unable to find the answer. It should be so simple but somehow things like these are for a noob impossible and even frustrating to figure out. There is a trigger option but you can't connect it to a light by dragging or adding a light to it).

The problem I'm having is that the directional light is always a little visible where it shouldn't be. I tried thicker walls and strengthen the shadow etc but it's still a little visible. Thank you in advance.