Use the Emissive Material Input
( Emissive Materials in Action )
With the room (-now) setup, it is now time to add some meshes for testing. Inside of the Starter Content folder, there is a folder labeled Shapes. Inside of that folder, you will find a mesh named Shape_Cube. Select the Shape_Cube with your Left Mouse Button and then drag the mesh from the Content Browser into the level releasing the Left Mouse Button when the mesh is over the level viewport. This will place the mesh in the level.
Now that the mesh has been added to level, it is (-now) time to apply the Emissive Material to it. To do this, locate the Emissive Material folder in the Content Browser. Once you find it, select the Material Instance with the Left Mouse Button and then drag the Material Instance from the Content Browser onto the Shape_Cube mesh.