Here’s how:
In your material, create a multiply between your emissive texture, and your shader. Attach a scalar parameter to this multiply and give it an appropriate name and default value (something like lamp_brightness).
In your blueprint, in the Construction Script, add a Create Dynamic Material Instance node, and point it to your lamp texture. Promote the output of that node to a variable, and give it a name.
In your event graph, when your light is triggered, you can use Set Scalar Parameter to change the value of the named scalar parameter on the fly. (NB: The below graph is slightly different, since I’m controlling my lights with a Matinee, but you should be able to figure out what to do…)
Hope that helps 