Astronomers can identify distant galaxies beyond the reach of our telescopes by the light they emit, focusing around other galaxies and stars closer to us. The developers of popular iOS game God of Light use some of the same (if somewhat exaggerated) gravitational properties of photons to craft an addictive and endearing puzzler. Observe:

In God of Light, you're a benevolent space being called Shiny, and the description is pretty apt. The point of the game is to get beams of light to their destination using a combination of mirrors, prisms, black holes, and other handy items that will transform and move rays of light 'round the game board and into the "Source of Life." (Remember that one scene with the mirrors from The Mummy?) That's all pretty simple, but it's the presentation that's worthy of attention: the only way to "see" around the level, and subsequently pick up the various baubles required to get the high score on each one, is to light them up with your frustratingly narrow beam.

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The no-rush pacing and soothing music put God of Light broadly into the "zen" subgenre, but anyone who's ever tried to work out a trick shot on a pool table should be able to find some enjoyment from this geometrical puzzler. The game is free, but offers in-app purchase "hints" in the form of fireflies that can better illuminate the levels. Sadly the game also features the odd advertisement too, but at least it's got Google Play Games support.