Light Up

Light Up, also known as Akari, is a Nikoli puzzle in which the aim of the game is to light up a grid by placing light bulbs on the white cells. The bulbs will shine in both horizontal and vertical directions, lighting up all the white cells in its path. The black cells block light.
The game can be played on any sized grid. The size of the grid doesn't always make the puzzle more difficult however, the positions of the black cells and the amount of number hints given is often what determines the difficulty level.

The rules are as follows:
- No two light bulbs can shine upon each other.
- All white cells must be lit up.
- Bulbs send light horizontally and vertically. The light continues until either the edge of the grid or until it hits a black cell.
- The numbers on the black cells indicate how many light bulbs are directly next to it (if any). Bulbs placed diagonally from a black cell do not count toward the total count.
- Black cells without a number can have any number of black cells.

Standard version

Light Up is perhaps one of the more time consuming Nikoli puzzles, but with some deduction work it's usually easy enough to solve within a relatively short amount of time. It's easiest to start with either a black cell that has the number 4 on it, meaning all sides will have a bulb, or with a numbered black cell that is blocked by other black cells, meaning the total options for placing bulbs around it has been reduced.

Another option is to look for more isolated cells and try to figure out how many possible options it could have to be lit, this often reveals some white cells can only be lit by 1 possible bulb placement.
The entire puzzle relies on deduction similar to this, so to the savvy puzzler it usually isn't too much of a hassle.

Converting it to an RPG setting.

Light Up provides a perfect opportunity for a darkness exploring puzzle, but other adaptations are possible as well (more on this later).
By having your players explore a cave or other area with light placements the tensions could rise, especially when avoiding monsters or finding loot relies on the correct placement of light bulbs.

In my example my character is trapped in a cave. The light brown cells are the cave ground and the black cells are steep cave walls, columns and other cave elements blocking light.
She's been told to place down and light braziers around the cave to ensure her own safety from those lurking in the dark, but she'll only be truly safe if she can light up the entire area. She's also given the information on how to solve a Light Up puzzle, with the twist that if she ever puts down and lights a brazier in a way that breaks the rules it'll explode, causing damage to her and perhaps alerting those that lurk in the dark.

If she does everything right she'll be able to light up the entire cave, which in turn will not only ensure her safety, but also trigger an event that allows her to move on to the next zone and the next part of the story.

As mentioned there are other adaptations you could make to Light Up. Instead of braziers you could have statues of guardians, which have to overlook all white cells. However, if they see each other they will come to life and fight each other or those in the cave.
Alternatively, you could think in a vertical plane and instead place bulbs in a cave entrance or other similar round gateway. The bulbs will form a net of lasers/magic/etc. covering all the white cells, creating a perfect protection barrier against anything that might try to pass through it.
There's far more you could do of course, but hopefully this guide and the examples thus far have given you enough inspiration to customize this puzzle to fit your personal story universe.