Follow the Light
Read the puzzle
On a 6 by 6 grid (rows from the top, columns from the left), a lamp left of row 4 shines right. Mirrors shaped \ sit at r1c1, r2c6, r6c1; mirrors shaped / at r2c3, r4c3, r6c4, r6c6. Panes: blue at r3c1 and r4c4, red at r5c6, yellow at r6c5. Doors: A above column 2, B above column 5, C right of row 2, D below column 4. Colours mix like paint. Which door does the beam light, and in what colour?
Colours mix like paint. Which door does the beam light, and in what colour?
D, ORANGE
Mirrors turn it; red and yellow panes make orange.
How to solve it
Trace the beam one square at a time and note every turn and every pane.
The lamp shines right along row 4. It passes columns 1 and 2, then meets the mirror in column 3, which slopes up to the right, so the beam turns up. It rises to row 2, column 3, where a second mirror of the same slope turns it right again.
Along row 2 it crosses columns 4 and 5 and hits the mirror in column 6, which slopes down to the right, so it turns down. Going down column 6 it passes the red pane in row 5, so the beam is now red. In row 6 the mirror turns it left, and it passes straight through the yellow pane in column 5. Red mixed with yellow, like paint, makes orange. The mirror in row 6, column 4 then turns it down and out through door D.
The answer is door D, orange.
The usual mistake is to let the beam run straight on along row 4 into the blue pane in column 4, but the mirror in column 3 turns it away first. Quick check: the beam crosses exactly two panes, red then yellow.
