Aiming the light from inside

We used a short card tube around each LED. It stops the light washing into its neighbours, so every pixel lights its own patch of cloud. The effect was probably quite small, but it helped a bit for finer-grained effects like lightning moving through the cloud.

We removed the tubes from the LEDs at the edges of the pyramid (the orange-lit photo), as it was actually useful for those LEDs to spread their light and cover more of the corners of the pyramid structure.