So, there was a solid concept here. Light is both your health and your bullets. Every shot was dangerous.
Enemies came in fast and hard. And you had upgrades.
But, due to how much light there was, it never came into effect. And the lack of enemy variety meant that I kinda got used to the game extremely quickly which took away a bit of tension.
Some upgrades were interesting, but after a certain point I just became immortal. Only way to die was getting stuck by enemies (I recommend for this genre, turning off enemy collision with the player so the player doesn't get stuck), but that never happened. Maybe a nice timer to give the player a winning condition too.
Also books and enemies got stuck at the "wall"? Alot? Meant there was alot of pick ups I couldn't get. And pick ups came too regularly regarding said books.
Honestly though, if you adjusted some things and added some more unique book items, there's a strong idea here. I could see myself running around trying to fire at every enemy I can to find some healing. Make that more brutal and you got a real high degree of tension with the game. Goodluck with the rest of the jam.