The signals from photoreceptors modify plant morphogenesis and regulate the timing of flowering. In the long-day plant petunia, flowering is accelerated under blue (B) and white (W) light compared to red (R) light. In Arabidopsis thaliana L., ELF genes are involved in circadian clock-associated regulation of flowering under different light conditions. In this study, we aimed to assess the involvement of ELF genes in control of flowering by light quality in petunia. Two ELF4-like genes, PhELF4-1 and PhELF4-2 with 76% and 70% similarity to orthologues in pepper but low overall similarity to ELF genes in A. thaliana L., were characterized in petunia and their expression patterns studied under different light qualities. Both genes showed a rhythmic expression pattern and higher expression under B light from light emitting diodes (LED) and W light from fluorescent lamps than under R LED light from LED. For both genes, the expression peaked towards the end of the day, 12 h after start of a 14 h photoperiod. Compared with PhELF4-2, PhELF4-1 expression showed higher amplitude with significantly higher peak expression. As investigated for PhELF4-1, such an expression rhythm was kept for two days after transfer of the plants to continuous lighting using B LED, indicating a circadian rhythm. PhELF4-1 also responded with a phase shift after transfer to short days of an 8 h photoperiod. These results indicate that PhELF4-like genes in petunia are under photoperiodic control involving a circadian clock and play a role in signal transduction from one or more B light photoreceptors.