A new bug with 4.9, if a light is on a hidden layer, it will not work in game.
I find it good to keep my lights and effects on their own layers, in 4.9 i found a bug that if a light is on a hidden layer, it will not display in game.
However if an effect is on a hidden layer it dsiplays in game (as intended)
This is a little frustrating…
Cheers 
Hi Gibbz,
This looks like an issue that was broken in 4.8 and is now fixed in 4.9.
If lighting is on a layer and that layer is hidden it should not render. In 4.8 the Billboard for the light would be hidden, but not the actual light itself.
Thank you!
Tim
Well i assume its a bug, as other stuff which is on that hidden layer is visible in the game 
So there’s no consistency there. In which case, anything on a hidden layer should then not render in game…
So there is a bug still there.
My mistake, looking into this further, anything in the Layers should only work while editing and not in PIE.
Apologies for the confusion on my part. 
I’ve entered UE-20890 for this. Once there is an update I will post back here.
Thank you!
Tim