The original version of this story appeared in Quanta Magazine.
Most of life’s engines run on sunlight. Photons filter down through the atmosphere and are eagerly absorbed by light-powered organisms such as plants and algae. Through photosynthesis, the particles of light power a cellular reaction that manufactures chemical energy (in the form of sugars), which is then passed around the food web in a complex dance of herbivores, predators, scavengers, decomposers, and more.
On a bright, sunny day, there’s a wealth of photons to go around. But what happens at low light? Biologists have long been curious about just how little light photosynthesis can run on—or how many photons need to