@Corona_GK
Thanks for the scene, I like the way you used the text so I copied it and made it a lot thinner. That's more the effect I'm looking for. The problem is still that there is a very bright light at the bottom but the top of the box doesn't glow at all. You can see it catches light but it's not bright enough to give a bloom or glare effect. This is not how it behaves in the real world unfortunately.
@romullus & Br0nto
I tried both things but it doesn't work. I tried using a rough material on the faces that needed it and also tried to use a texture as a mask for a rough material. The light does not catch the rough faces like it would in the real world. Make the faces into an emitter works, but I need different colours and lights from different directions to mix with each other and thus give a different effect than just one bright emitter. I did a test with a rough material on the edges but the edges just don't light up bright enough. In the image below I set the emitter to an insanely high value (500.000 lux) and it kind of works but it ends up over lighting the scene. So I included only the box in the lights and that works better but when I turn on bloom and glare I get this superbright spotlight.
So you can see the colors of the light mixing, which is good, but again the lights have to be very bright and I'm afraid that's not workable for me. I haven't tried using a falloff effect because that takes a lot of time to get right, I'll see if I can later today but I'm on a tight deadline (isn't it always the case).