What green pigment captures light energy in photosynthesis?

The green pigment that captures light energy in photosynthesis is chlorophyll.

Chlorophyll is a family of related pigments found in plants, algae, and cyanobacteria. In green plants, chlorophyll molecules are embedded in protein complexes within the thylakoid membranes of chloroplasts, where they absorb photons and help convert light energy into chemical energy.

Chlorophyll absorbs light especially strongly in blue and red portions of the visible spectrum, while reflecting more green light. That reflected green light is why leaves and many algae appear green. Chlorophyll a is the primary photosynthetic pigment in oxygen-producing photosynthetic organisms; chlorophyll b helps broaden the range of light collected by many plants and green algae.

Carotenoids and xanthophylls are accessory pigments that also assist with light capture and protect photosynthetic machinery. Phycobilins perform related roles in cyanobacteria and some algae, but the standard answer to this question is chlorophyll.