make Goggles of revealing, incase the node in glass leaving 2 free blocks around it to form a cube or at least 7x7x7 inside, add a tesla coil 1 to 2 blocks over the node powered in anyway you wish, have is on a button push, & now you have a wisp grinder, you can add a TC wooden golum & a chest if you like to pick up the essences for you, the 2 vanilla spawners can be turned into xp/item grinders with ease, if you make a grav gun you can move them to a room made with lamps over the replaced spawners to have an OFF switch, I'll not go into that build we all know it.
btw light lvls have no effect on wisp spawning, the flux lvls in the area make them spawn more often, so doing lot of TC will create lots of wisps.