What is the black box game?
The black box game is a deduction puzzle where you can’t see the board. Balls are hidden inside a square box, and the only way to find them is to fire beams in from the edges and watch what happens. A beam might be absorbed, bounce straight back, or bend and come out somewhere unexpected. From those clues you work out where the balls must be.
It feels like detective work with a laser. Play Black Box online free here, on boards from 5×5 to 10×10.
Where Black Box comes from
Black Box was created by Eric Solomon and published as a board game by Waddingtons in 1977. In the early 1980s Acornsoft brought it to the Acorn Atom and BBC Micro home computers. In the board game, one player could hide the balls while another fired the beams. Here the computer hides them for you.
How to play here
Pick a board size on the start card, then press Play. Click or tap a square around the edge of the box to fire a beam, and the result appears at once. Tap a result again to highlight that shot. Click or tap inside the box to place a guess, and tap again to remove it.
To lock a square so you can’t change it by accident, right-click it, or on a phone turn on Mark in the dock and tap it. Locking an edge square locks its whole row or column. Once you have placed the right number of guesses, a check button appears at the top-left corner of the box. If you’re wrong, the game shows you one beam that proves it.
Undo, Redo and New puzzle are in the dock, and Solve in the pause menu reveals the answer.
How the beams move
- Straight on: with no balls nearby, a beam crosses the box and leaves on the far side.
- Hit: a ball directly in its path stops it. You see H.
- Turn: a ball diagonally ahead on one side, with nothing straight ahead, turns the beam 90 degrees away.
- Reflect: if it ends up leaving where it came in, or is turned away at the very edge, you see R.
A beam can turn several times before it leaves or hits a ball, so a numbered pair can be the end of a long, winding path.
A step-by-step way to solve
- Fire a spread of beams. A few shots from each side give you an overall picture.
- Use the edge Rs. An instant R often places a ball in the first row inside. Check it against other shots.
- Trace the numbered pairs. Work out which turns would carry a beam from one point to the other.
- Test your theory. Fire a beam whose result you can predict. If it surprises you, rethink.
Why play Black Box?
It’s unlike any grid puzzle: you gather your own clues, and every shot is a choice. For more hidden-information logic, try Minesweeper or Code Breaker.
How to play Black Box
- A few balls are hidden inside a square box. You find them by firing beams in from the edge.
- A beam that runs straight into a ball is absorbed and shows H, for hit.
- A beam that passes a ball sitting diagonally ahead of it turns 90 degrees away from that ball.
- A beam that comes back out where it went in, or is turned away before it even enters, shows R, for reflected. Any other beam shows the same number where it enters and where it leaves.
- Place your guesses and press the check button. You win if your balls explain every beam.
Black Box tips
Read the R at the edge
An R straight away often means a ball in the first row inside the box, diagonally next to where you fired. A ball directly in front gives an H instead.
Spread your shots
Fire from several sides before you guess. Beams that cross each other tell you far more than shots from one side.
Treat straight exits as hints
A beam that comes out directly opposite probably crossed an empty line, but two turns can bring it back onto the same line. Check before you rule the line clear.
Frequently asked questions
How do you play the black box game?
Click a square on the edge to fire a beam. The result tells you whether it hit a ball, bounced back, or came out somewhere else. Use those results to place your guesses inside the box, then press the check button.
What do H and R mean in Black Box?
H means the beam hit a ball head-on and was absorbed. R means it was reflected, either leaving where it entered or being turned away right at the entrance. A number marks a beam that entered at one point and left at the other point with the same number.
Who invented Black Box?
Black Box was created by Eric Solomon and published as a board game by Waddingtons in 1977. Acornsoft released computer versions for the Acorn Atom and BBC Micro in the early 1980s.
Can there be more than one right answer?
Yes, when there are more than four balls. Some layouts give exactly the same beam results, so the check accepts any layout that matches what the beams show.
