Multichannel flash spectroscopy (with microsecond time resolution) has been applied to carotenoid (Car)-containing and Car-less reaction centers (RC) of Rhodobacter sphaeroides with a view to investigate the interaction between the Car and its neighboring pigments at room temperature. Under neutral redox potential conditions, where the primary quinone acceptor (Q_A) is oxidized, the light-induced spectral changes in the 350–1000 nm region are attributed to the photochemical oxidation of the special pair (denoted here as P₈₇₀), the generation of P ₈₇₀Q⁻_A, and the attendant electrochromism of adjacent chromophores. A bathochromic shift of <1 nm in the visible absorption region of Car reveals the sensitivity of Car to the P₈₇₀ photooxidation. Under low redox potential conditions, where Q_A is reduced, P₈₇₀ triplets (P^†₈₇₀) are formed. The time-resolved triplet-minus-singlet (TmS) spectrum of Car-less RC shows a deep bleaching at 870 nm, which belongs to P^†₈₇₀, and additional (but smaller) bleaching at 800 nm; the entire spectrum decays at the same rate (with a lifetime of about 50 μs). The bleaching at 800 nm arises from the pigment interaction between P^†₈₇₀ and the accessory bacteriochlorophylls on A and B branches (B_A,B). In Car-containing RC, the TmS spectra of Car are accompanied by two smaller, negative signals—a sharp peak at 809 ± 2 nm and a broad band at 870 nm—which decay at the same rate as the TmS spectrum of Car (ca 10 μs). The former is ascribed to the perturbation, by Car^†, of the absorption spectrum of B_B; the latter, to the TmS spectrum of P^†₈₇₀, a species that appears to be in approximate thermal equilibrium with Car^†. These assignments are consistent with the absorption-detected magnetic resonance spectra obtained by other workers at low temperatures.