In a sequential removal puzzle pieces have to be removed in a sequence. Doing it in the wrong order will lead to a dead end. Lights Out is also a puzzle in which something has to be removed (all lights have to be turned off), and as a user you will perform actions sequentially. However, it turns out after some more pondering over the solutions that the order of actions is not important. So, strictly speaking this is not a sequential removal puzzle, but it definitively feels like one.
Lights Out consists of a grid of lights; when the game starts, a set of these lights (random, or one of a set of stored puzzle patterns) are switched on. Pressing one of the lights will toggle it and the four lights adjacent to it on and off. Diagonal neighbours are not affected. The aim of the game is to switch all the lights off. The following straightforward Lights Out implementation are available in the app store [links redirect to iTunes]:
- Lights Out
- Lamp Off
- Night Lights [Lite version]
- Christmas Lights Off
- Touch Ghosts
- MosaicGame (note that the touched tile itself does not switch in this one)
Of course you will by now, after reading some of my previous posts, not be surprised to hear that not one of these games does refer to the origin of this puzzle concept in any way. In this case, however, it turns out that it is actually not that easy to point to one clear origin (see the terrific summary by Tony Delgado of the history of this kind of puzzles). The name Lights Out and the precise rules as described above go back to a physical electronic puzzle produced by Tiger Electronics in 1995 (shown here to the left). However, there is a long history of conceptual predecessors that could also be mentioned (see Tony Delgado’s history for the details, and see also Jaap Scherhuis’ extensive collection of information about this puzzle).
There are a two apps for the iPhone that take this principle a bit further. First, Quantum Lights adds more than two states for the lights. Instead of going on-off-on-off, the lights will cycle through a set of states/colors (the more states, the more difficult it gets). This principle was also used by a sequel to the original physical Lights Out, called Lights Out 2000, which had three different states. I did not try Quantum Lights, but I expect that more than three states/colors becomes too complex for a normal human being seeking some diversion.
The second variation is that it is of course not necessary to apply this principle to a rectangular board. The generalization to play Lights Out on any directed graph was already proposed long before lights out itself appeared (Klaus Sutner 1990). To some extent, a more complex graph was already implemented physically in the Lights Out Cube. A very nice implementation of a non-rectangular graph to play Lights Out is now available in the app store as RedState/BlueState. In this game you are given a map of the USA with all states colored according to their republican or democratic vote majority. If you press a state, it will change it color, and so will all neighboring states. The goal is of course to change the USA vote according to your political preference. The graphics look a bit poor in the screenshots, but the underlying puzzle sounds very interesting!
[Update 21 January 2009] Black Out just became available in the app store. It is a literal remake of the original Lights Out, and it even says so: “Black Out is a remake [of the] addicting puzzle game originally brought to you by Tiger Electronics in the 1990’s”.
[Update 22 January 2009] Lights Off just became available in the app store. The same thing once again. The only reason for a little bit more attention for this version is that this was apparently the first game written natively for the iPhone, in pre-app-store jailbreak times (ages ago…).
[Update 22 January 2009] I seem to have missed a few Lights Out clones in my survey: Lights Off Puzzle and Christmas Holiday Lights. One has to be amazed about the inventiveness of developers to come up with different names for the same thing.
[Update 24 January 2009] I have no idea what is going on here, but today yet another Lights Off clone arrived in the app store: BlackOut: Lights Off Game. My earlier comment on inventiveness when it comes to names applies here too!
[Update 29 January 2009] The next one: EZ Light. Do they really think nobody notices? Probably they are right…
[Update 6 February 2009] Behold, there is still innovation! In Flick Off you can “change the flip style from adjacent to diagonal”. Did nobody tell them, that that is identical to changing the board form? They should read the Sutner paper I linked above.
[Update 22 February 2009] An interesting variation on Lights Out is Bulbs. Instead of just one orthogonal square to each side, the complete row and column of the choses square changes color. My first intuition says that this is equally complex as the classical Lights Out, but I cannot immediately see the complete consequences. Nice!
[Update 23 February 2009] The next classical Lights Out implementation: Light Bulbs.
[Update 31 March 2009] Tap Flip Challenge.
[Update 29 April 2009] An interesting Lights Out variant just became available: Clack! In this one, every tile has a separately specified behavior as to which of the neigboring tiles also switch. Sounds like a nice variation!
[Update 30 April 2009] Another one: Trixel. In this one turning a tile either turns all orthogonally connected tiles as well, or alternatively all eight tiles around the centre.
[Update 7 May 2009] A nice variation: Leds. Instead of the classic orthogonal pattern from Lights Out this one also has options like a knight’s jump pattern (all tiles change that are a knight’s jump away from the chosen tile) and it allows for the field to be interpreted as a torus, so if you chose a tile on the border, tiles at the other side of the board will change as well. (see also my earlier post on torroidal sliding block puzzles in the app store). Also three different states are possible, like in Quantum Lights.
[Update 22 May 2009] All Lights.
[Update 26 May 2009] Puzzle On Off.
[Update 6 June 2009] Ligths Out on a torus: All Switches On. In practical terms, this means that the sides of the board are connected, so the neighbors swap around the board. See also the list of toroidal sliding block puzzles in the app store.
[Update 16 June 2009] A slight variation on the Lights Out theme: Logic Bulbs. All orthogonal adjacent lightbulbs change state, but the tapped bulb itself does not change. Interestingly, the different levels consist of selected number of bulbs of the grid (so not all points in the grid have a lightbulb).