Significance Photosynthesis uses carotenoids as light-harvesting pigments and for photoprotective energy dissipation. The carbon–carbon double bond conjugation length of carotenoids ( N ) affects the carotenoid-to-(bacterio)chlorophyll energy transfer efficiency, but the photoprotective capability was considered to be independent of N . Using light-harvesting complex 2 from the model photosynthetic bacterium Rhodobacter sphaeroides containing ζ-carotene ( N = 7) or neurosporene ( N = 9), we demonstrate that decreasing the conjugation length increases the carotenoid-to-bacteriochlorophyll energy transfer efficiency, in the case of ζ-carotene to ∼100%. However, unity quantum efficiency comes at the cost of photoprotection, suggesting that naturally evolved photosynthesis tolerates some energetic loss to allow essential energy dissipation, explaining why longer-conjugation length carotenoids are utilized in native pigment–protein complexes.