At the start of the correction, what looked like a wall of Light spread out from all the balls of Light which landed across the planet. The Light Walls move slow enough that Jack was able to walk behind one to get a clear view of it's make up. The Lights use these walls to spread anything the need to across a large area.
From a distance, the walls appear to be made from nothing more than a shimmering, undulating, sheet of light. But they are actually a wall built from trillions of light threads. The threads used in the walls are much longer than the ones Jack and the rest of humanity use in their bodies, but they are functionally equivalent. Up close, they look like a sheet of glowing threads blowing in a light breeze.
The wall Jack and Fred saw had glowing Lights moving from the top to bottom. These lights were actually high voltage electrical charges which were being used to burn out all the electronic devices on the planet. What they didn't notice were the other short threads being injected into the ground by the wall. These secondary threads were programmed to cause make all plant life grown exponentially for two days. The walls could be use to deliver anything that was build on the same scale as the threads.
One thing that confused most people was where these walls of Light came from. They appear to be enormous, expanding the width of large cities and extending above the tops of office towers and the balls of light were only ten meters wide at most. But since a typical thread is only a few atoms wide, a wall that size can be easily compacted into a small space.