In your door blueprint, add a public variable for your light (new variable>search>reactlight>object reference (if you use this way, be sure to specify the light in the details panel when you click on the door bp in the world)). you might already have a reference to the light in the bp if so, use that. Then use a map ranged clamped node and use the rotation of the door to drive it. the input values are the min and max values of the door rotation, and the output values are the light intensity you desire. Use the return value to change the intensity of the light.