One beam, many zones, ration the single spotlight to grow each zone before the dark wilts it.
Your terrarium holds several zones of growing organisms, but you own only one beam of light. Each tick you point it at a single zone, that zone glows and grows while every other zone dims and declines. A zone left in the dark too long dies. Keep them all alive across the run and grow as much total biomass as you can.
Photosynthesis is the constraint the whole design rests on: without light, a plant does not merely stop growing, it declines.
The original element is scarcity of attention rather than of resources. You own one beam, and the zone you point it at grows while every other zone dims.
That makes neglect an active cost rather than a pause. Most rationing puzzles divide a stock; this divides a single indivisible thing across time, so there is no allocation that keeps everything healthy — only a rotation that keeps nothing quite dying.
Borrowed Light reimagines the resource-rationing puzzle as a fragile garden tended by a single spotlight, where attention itself is the scarce resource. It is an original, free browser game on PlayPendium with daily and practice modes.