Rules: The challenge is to draw a loop around the grid and light up all white cells, subject to the following rules:
- White circles must be travelled straight through, but the loop must turn in the previous and/or next intersection in its path.
- Black circles must be turned upon, but the loop must travel straight through the next and previous intersections in its path.
- The loop mustn't cross or branch off.
- Numbers in the squares represent how many of its four sides contain a lit cell.
- All White cells must contain part of the loop or a lit cell.
- Each lit cell illuminates all white cells in a horizontal and vertical direction until the beam hits a black cell or a wall.
- Lights cannot shine on each other.