phototaxy

/ˈfoʊtoʊˌtæksi/
noun
  1. The movement of an organism or cell toward or away from a source of light.
    • Many insects show phototaxy, flying toward streetlights at night.
    • Scientists use phototaxy to study how simple creatures respond to light.
    • Algae exhibit positive phototaxy by swimming toward the water's surface.
Synonyms