First of all, this is not to be confused with the somewhat controversial Luminosity program from Lumos Labs.
Luminosity is an arcade score attack game by an independent developer by the name of Windmill Games. There's a lot of games that strive to be 'retro' and evoke the old 8-bit or 16-bit days of the NES/SNES and Genesis, but Luminosity is a game that doesn't really bill itself as retro but nonetheless achieves that feel. It very much feels like some sort of modern version of an Atari 7200 game. And I don't mean to be derisive in that comparison.
A lot of gaming in that era of the Nintendo/Famicon, Genesis, Intellivision, et al, was spent trying to replicate the quality and experience of an arcade cabinet. And Luminosity feels like that arcade cabinet game that Atari games were trying to replicate. It feels like it would have been one of those. For a simplistic game, there's a kind of inordinate amount of polish into the actual game design. It shows a certain level of careful attention that is the exception rather than the rule for the gaming industry
The gameplay of Luminosity is pretty simple indeed: you control a pong-like paddle which creates lines subdividing the screen, and you are attempting to cordon of increasing amounts of the screen. There will be a series of bouncing obstacles and your beam or line does not create automatically, but rather must travel to the edges of the screen. If it collides with one of the obstacles you take damage. And other than some powerups or increasingly difficult obstacles, that's about what there is to it.
Personally, I would rather a game like this that does a very simple set of mechanics with a great deal of proficiency and care than a more complex game that flops. Unfortunately, with Steam how it is, there's a lot of much more complex games you can get for the same price point. It may be best to get it in a bundle or on a sale. But nonetheless, it's worth picking up, in my opinion. It's a well-made game that does exactly what it sets out to do.