Light is fundamental - it interacts with life in profound ways. It tells us when to sleep, wake, eat; it tells plants which way to grow, birds where to fly and coral when to spawn. But light is changing, dramatically, and we don't truly understand the consequences. Nature writer Anna Levin explores the impact on the planet and on human health.

Spring marks the genesis of nature's year. As Earth's northern hemisphere tilts ever more towards the life-giving sun, the icy, dark days of winter gradually yield to the new season's intensifying light and warmth. Nature responds... Jim chronicles it all: the wonder, the tumult, the spectacle of spring.