Sunlight influences an array of biochemical processes in plants, animals, fungi, and bacteria. In numerous organisms, phytochromes—a special class of photoreceptors—absorb red or far-red light and transform it into signals that trigger corresponding physiological reactions. In Nature Communications, an international team including scientists from Bayreuth has now reported a surprising discovery: two bacterial phytochromes function in contrasting ways despite having a similar structure. These findings offer new starting points for research into light-controlled processes in nature and for biotechnological applications.