Photoperiodic injury (PI) in tomato is characterized by leaf chlorosis & necrosis when exposed to continuous (CL) or non-24-h artificial lighting photoperiods, suggesting a role for the circadian clock. PI is less obvious under high-latitude natural CL, thus it was hypothesized and discovered to have shifting solar spectra with geo-temporal information to clock inputs like phytochrome. In addition, circadian outputs including N-assimilatory enzymes become arrhythmic in PI-intolerant ‘Basket Vee’ (BV) under CL, whereas they do not in PI-tolerant ‘Micro-Tom’ (MT). Recently reported PI-tolerance from a light harvesting complex (LHC) gene was hypothesized to alter chlorophyll regulation’s effect on reactive oxygen species (ROS) rhythms such as superoxide. MT and BV shared similar short-term (<24hrs) CL acclimation through increased chlorophyll (Chl) contents, Chl a/b, PSII operating efficiency (YII), and dampening of superoxide rhythms. Unexpectedly, long-term (>5days) CL further damped rhythms regardless of cultivar while only BV’s Chl content dropped, and YII destabilized.