I’d like to be able to use meshes as lights through the emissive channel, but it seems that feature isn’t available in UE4. Unless I’m missing something–just putting that out there because there’s cases where a point or a spot light don’t give the lighting the way I need it.
I think it’s supposed to work, there is a toggle for in in the material settings, but I have yet to get it to work. It certainly does not work like it does in UDK/UE3 (which did have it’s bugs, but otherwise looked great). I was trying to get it to work last night, but no joy. I wonder if it’s temporally disabled while they fix some of the bugs that existed in UDK? It’s an important feature to how I like to light (coming from an offline background), and now that you cannot have lights overlap how you light with lights have changed considerably and emissive lighting really is the only way some kinds of things will work correctly if I cannot stack lights close together.
You can have lights overlap, you have to change the light type to Static.
I haven’t found any way to use emissive materials for lighting, so hopefully there will be some way of doing it.
Have a look at this! 
Its actually not supported for static lighting right now (as explained in this thread) but it should work for dynamic lighting if you enable the BETA feature “light propagation volumes”.
However, they are not yet meant to work without errors since the feature is not fully done.
That doesn’t work. LPV works but can’t get anything from emissive lighting.
Yeah it doesn’t work with LPV.
That being said, there is no emissive lighting for quite some time already, I don’t think there are even plans to bring it back right now.
Yeah I saw that they had it disabled after I posted my response.
Disappointing to be sure, I hope at some point they come out with a real-time GI type solution that allows this. 90% of what I do is cinimatic in nature rather than game play, so I personally am less concerned about any performance hit that I incur since I am rendering frames sequentially to file. Any game play stuff that I do is directed towards mobile so I doubt that I will be running anything with max feature setting at that point. 
@darthviper107: thanks for the tip! it was turning my overlapping lights into “real-time only” lights during the baking process. So thank you. 