Why does adding a visible light to my pawn affect velocity?

Hello there. Sorry if this has been asked in the past. I’m still learning the ropes and something has me stumped…
I’ve created a helicopter as my pawn which uses “set all linear physics velocity” to calculate its movement, which takes the yaw/rotation/pitch into account. What I’ve noticed is after I’ve added a point light to the pawn it then requires more power to lift off as if the light adds mass. I’ve experimented with this and added a simple set visibility key to the lights. If I hover with the lights off and then turn them on the helicopter starts to descend. Another strange thing is if I add the same static mesh that is used by my pawn to the scene it also affects how much power is needed to lift off, but only when the mesh is in view. Any advice here would be greatly appreciated, its driving me a little potty.

After a bit or experimentation it appears the “Cast Shadow” option on the lights is causing this. Any ideas why?