4 x 4 x 4

In each grid, normal 4x4 sudoku rules apply. The grids are numbered 1-4 in normal reading order. 2x2 boxes within each grid are numbered 1-4 in normal reading order. Cells within each 2x2 box are numbered 1-4 in normal reading order.

Reading along a coloured line (starting at the end with the invisible bulb), the digits WXYZ indicate that in grid W, box X, position Y, a digit Z should be placed. Every line indexes a different cell, which always happens to be located somewhere on a line.