"Edith Widder grew up determined to become a marine biologist. But after complications from a surgery during college caused her to go temporarily blind, she became fascinated by light as well as the power of optimism. Her focus turned to oceanic bioluminescence ... On her first visit to the deep ocean, in an experimental diving suit that took her to a depth of eight hundred feet, she turned off the suit's lights and witnessed breathtaking explosions of bioluminescent activity. Concerns about her career went out the window. She just wanted to know one thing: why was there so much light down there? ... Alongside Widder, we experience life-and-death equipment malfunctions and witness breakthroughs in technology and understanding, all of it set against a growing awareness of the deteriorating health of our largest and least understood ecosystem"--