The Core at the centre is the only light in this place — and it is also your life. Mana builds gems, grades gems, and is the exact quantity a breach takes from you.
Gems are not turrets. Every gem must receive light from the Core, directly or relayed through other gems, and intensity decays at every hop. A gem in the dark does nothing. Walls block creeps and block light alike.
Light is a budget, not a gift. It weakens at every hop, and it splits between everything a node feeds — a Core supplying six gems gives each far less than one supplying two. Grading up raises what a gem passes on, and a Prism splits far more cheaply than a gem. Long thin chains and fat stars are both traps.
Shards are paid by depth, never by victory — a run that ends on wave 40 pays forty waves' worth. Quitting is never correct and losing is never wasted.