Laser Router

One beam, two mirror angles, ninety seconds — bend the laser around three blockers before the bulb goes dark on you.

Updated July 16, 2026

Routing the Beam to the Target

Laser Router puts a beam emitter in the top-left corner of a 5x5 grid and a target bulb in the bottom-right corner, diagonally opposite. The blue LSR cell fires the beam to the right the instant the round starts; the amber BLB cell is your destination. Everything between those two corners is either open floor, one of three dark obstacle blocks, or a cell you can turn into a mirror.

You interact with exactly one control: click a cell. The first click drops a / mirror, a second click flips it to a \ mirror, and a third click clears it back to empty. Obstacle cells and the emitter/bulb cells themselves aren't clickable — mirrors only go on open floor tiles. Every click immediately recalculates the beam's route from scratch, so there's no separate "submit" step; the puzzle solves itself the moment your mirror layout sends the beam onto the bulb cell, from any direction.

Winning is binary. Land the beam on the bulb and you win the round outright, 1 point to your opponent's 0. Fail to route it before the clock hits zero — or, in a ranked duel, before the bot finishes its own board first — and the loss goes the other way. There's no partial credit for a beam that gets close, and nothing carries over between rounds: the obstacle layout is regenerated from scratch at the start of every match.

Mirrors, Angles and Blockers

Both mirror types redirect the beam by exactly 90 degrees, and which way it turns depends only on the direction the beam was already traveling when it hit the mirror:

• / mirror: a beam moving right turns up; a beam moving left turns down; a beam moving down turns left; a beam moving up turns right.
• \ mirror: a beam moving right turns down; a beam moving left turns up; a beam moving down turns right; a beam moving up turns left.

The two mirrors are mirror images of each other — for any incoming direction, / and \ send the beam to opposite 90-degree turns. That's the whole toolkit. There's no diagonal pass-through and no mirror that lets the beam continue straight; an empty cell just lets it keep traveling in whatever line it's already on.

The three dark obstacle blocks are absolute stops, not deflectors. If the beam's current heading runs it straight into one, the trace ends right there — no bounce, no partial glow past that point. The grid's outer edge behaves the same way: if a straight run or a mirror sends the beam off the 5x5 board on any side, it simply exits and the trace stops. Obstacles are placed fresh each round from the 23 cells that aren't the emitter or the bulb, so which routes are actually blocked changes from puzzle to puzzle.

Reading the Board Before You Move

Every click triggers a full re-trace, not a local patch. The engine starts at the emitter, walks the beam cell by cell in whatever direction it's currently heading, applies any mirror it crosses, and keeps going until it hits the bulb, an obstacle, or the grid edge. The entire resulting path is then painted in translucent red with a soft inner glow, cell by cell, so you can see the live route at a glance instead of mentally simulating it.

That matters because it turns "did that mirror help?" into something you can just look at. Place a mirror and the red trail either extends further toward the bulb, dead-ends earlier than before, or reroutes somewhere unexpected. If your last click made the red path shorter or sent it straight into an obstacle, that's immediate, unambiguous feedback that the placement was wrong — cycle that cell again rather than stacking another mirror on top of a bad one.

The emitter cell stays blue and the bulb cell stays dark amber throughout, so neither is ever mistaken for part of the traced path. The moment the trace actually reaches the bulb cell, it flips to bright lime and the round ends immediately — there's no confirmation step beyond that; the live redraw is the win condition firing in real time.

Planning the Whole Path

Because any mirror can be reset with a third click, it's tempting to place-and-check one cell at a time and let the red trace do all the thinking. That works, but it burns clock. A faster approach is to plan the shape of the route before you place anything: the beam only ever travels in straight horizontal or vertical runs between mirrors, so a solved board is really just a sequence of straight segments connected at turn points.

Pick a waypoint — a row or column where you'll switch the beam from horizontal to vertical travel — and check that no obstacle sits anywhere along either straight segment leading to and from it. Since the bulb can be reached from any direction, there's no requirement that the beam arrive from a particular side; you just need the last straight run to end exactly on the bulb's cell.

One thing to actively avoid: building a loop. If your mirrors route the beam back into a cycle — a set of turns that leads it right back through a cell it already crossed, still short of the bulb — it will circle instead of exiting or hitting anything, and the trace simply won't reach the target. If your red path seems to freeze in the same shape no matter what you add downstream, break the loop itself rather than adding more mirrors further along the route. Players used to grid-based logic puzzles like MathDoku will recognize the instinct: lock in the constrained cells first, then solve the tight corner last.

How Puzzles Scale in Difficulty

The board itself doesn't scale. Every round is the same 5x5 grid, the same corner-to-corner emitter and bulb placement, and the same count of three obstacles — Laser Router never grows to a bigger grid or drops in more blockers as you play. What changes round to round is where those three obstacles land: they're picked by shuffling all 23 open cells and taking the first three, so the actual blocking pattern — and therefore how many turns you need and which routes are open — is different almost every time you load a new puzzle.

The 90-second clock is fixed too, in both Practice and ranked Duel. It counts down the same way regardless of mode, switching to a red "hurry" state with an audible tick once it drops to 10 seconds or less.

Where difficulty genuinely scales is the opponent, in Duel mode. Each bot is assigned a solve time of max(15, 80 − (opponent's ELO − 1200) × 0.05) seconds, then that number is multiplied by a random 0.8–1.2 factor for natural variance. A bot sitting around 1200 ELO averages roughly 80 seconds to finish its own board; push the opponent's rating up toward 2200 and that solve time gets squeezed down toward the 15-second floor, meaning a genuinely strong bot can light its bulb before you've placed your third mirror. You get a rough read on where it stands from its status line, which shifts through "Aligning vectors..." partway through its internal timer and "Reflecting emitter beam..." as it nears completion — treat those messages as a countdown to how much time you actually have left.

A Solved Board, Move by Move

Say your puzzle deals obstacles at (row 0, col 3), (row 2, col 0), and (row 4, col 2), using row/column coordinates with (0,0) at the emitter and (4,4) at the bulb. Here's a full solve using nothing but \ mirrors:

• The beam fires right from the emitter and crosses (0,1) and (0,2) in a straight line.
• Click (0,2) to drop a \ mirror. A rightward beam hitting \ turns down, which routes it away from the obstacle sitting one cell further along at (0,3).
• The beam now runs down column 2 through (1,2) and (2,2), heading toward (3,2).
• Click (3,2) to drop a second \ mirror. A downward beam hitting \ turns right — the move that avoids the obstacle at (4,2), which sits directly in the beam's old downward path one row further on.
• The beam now runs right along row 3 through (3,3) and reaches (3,4).
• Click (3,4) to drop a third \ mirror. The rightward beam turns down again, and the very next cell is (4,4) — the bulb.

Three mirrors, three turns, zero wasted clicks: the red trace stretches from the emitter, bends twice through the middle of the board, and lights the bulb lime green the instant it lands. Both obstacles this layout actually threatened — the one at (0,3) that would have stopped a beam still running straight along row 0, and the one at (4,2) that would have stopped it running straight down column 2 — get avoided by turning one cell early, not by any complicated detour. That's the general shape of most Laser Router solves: find the obstacle that blocks your current straight line, and turn just before it.

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