Bah. 
Hmm…
Another wild guess here: You could unplug the base color from the material you are using for the Niagara smoke sprite and instead plug into emissive as the color. I believe emissive isn’t affected by light.
Bah.
Hmm…
Another wild guess here: You could unplug the base color from the material you are using for the Niagara smoke sprite and instead plug into emissive as the color. I believe emissive isn’t affected by light.