Why fireflies?

Every lights-out puzzle has the same goal: switch all the lights off. I love the puzzle, but “turn everything off” always sounded like bedtime chores to me. So we gave the lights a reason to go dark.

In our game it’s dusk in the garden, and every glowing patch of grass is a firefly. Calm them all down and they float up together into a glass jar. The jar glows a little brighter with each level you clear, and after 20 levels it shines like a lantern. Fireflies are the one bit of nature kids already think of as lights, so they fit.

A bit of real lights-out history

In 1978 Parker Brothers sold Merlin, a handheld electronic game with six games built in. One of them, Magic Square, was played on a 3 by 3 grid of lights, though its moves worked a little differently. Jaap’s Puzzle Page calls it probably the first game of this kind.

Around 1983 Vulcan Electronics made the XL-25, a game with a 5 by 5 grid of 25 buttons. It was invented by László Mérő, a Hungarian psychologist. Then in 1995 Tiger Electronics released its own 5 by 5 handheld and called it Lights Out.

The puzzle hides some neat math. Pressing a square twice is the same as never pressing it, and the order of your presses doesn’t matter. That makes it a linear algebra problem where the only numbers are 0 and 1, and one plus one makes zero. Marlow Anderson and Todd Feil wrote it up that way for Mathematics Magazine in 1998. On a 5 by 5 board, only one pattern in four can be solved at all. Our levels start dark and get scrambled with real presses, so every one can be solved, and the page uses the same math to count the fewest presses.

Real fireflies

Fireflies aren’t flies. They’re beetles, and there are about 2,000 kinds. A firefly makes light in its belly by mixing oxygen with a chemical called luciferin. This is called bioluminescence, and it makes almost no heat. Fireflies mostly flash to find a mate, and each species has its own flashing pattern. Males fly and blink, and females on the ground flash back. Firefly larvae can glow too, as a warning that they taste bad. And in some places, big groups of fireflies blink at the same time.

Three evenings

• Early dusk: levels 1 to 20 on a 3 by 3 patch. Every pattern here has exactly one best answer.
• Twilight: levels 21 to 40 on 4 by 4. Some patterns have more than one best answer.
• Starry night: levels 41 to 60 on 5 by 5. The last levels need 11 presses.

How to play

• Tap a patch of grass. It flips, and so do the patches above, below, left and right of it.
• Get every light out and the fireflies float up into the jar.
• Match the fewest presses for three stars. Up to 3 extra gets two stars. Every finish gets at least one.
• Undo takes back your last press. Restart begins the level again.
• Show me lights up one patch from a best answer. You get 3 per level.
• On a keyboard, arrow keys move and Enter or Space presses.
• Sound is on to start. Tap 🔊 to mute, or 🎵 for music.
• Earn 3 stickers in this game for your QuickBOP sticker book.

Tips

Order doesn’t matter. The same presses in any order end in the same place. Think about which patches to press, not when.

Never press a patch twice. A second press cancels the first. A best answer uses each patch once at most.

Clear from the top down. For every glowing patch in the top row, press the patch right below it. That puts the top row out. Repeat row by row and the lights gather in the bottom row, which is easier to read.

Corners are gentle. A corner patch flips 3 squares, an edge patch 4 and a middle patch 5.

Your turn

The garden is getting dark at the top of this page. Tap your first patch of grass and send the fireflies home.