Instructions
Place one of your three triangle-shaped box mirrors on the square that is two spaces to the right of and four spaces below the left light source. Box mirrors allow the light to pass through them in multiple directions. Make the tip of the triangle face right to cause the bottom-right light source to illuminate both a crystal and a reflective mirror.
Place your second box mirror six spaces to the right of the left light source. Make its light-receiving tip face left.
Place your final box mirror three spaces to the left of the upper-right light source. Make this triangle face right.
Place one of your two diagonal reflective mirrors five spaces below the non-illuminated crystal that is farther to the left. Rotate it left or right until the light reflects upward and illuminates the crystal.
Place the final reflective mirror 13 spaces below the final light that is still darkened. You can tell where this space is more easily by looking for the red light that goes horizontally across that row of spaces. Rotate the mirror until the light reflects upward, illuminating the final crystal. The puzzle is completed, and the barrier will lower momentarily.