Component of the central CCA1/LHY-TOC1 feedback loop in the circadian clock that promotes clock accuracy and is required for sustained rhythms in the absence of daily light/dark cycles. Part of a corepressor complex consisting of ELF4, ELF3, and LUX involved in the transcriptional regulation of APRR9. Increases ELF3 nuclear distribution and localization in nuclear bodies. Required for responsiveness to continuous red, by regulating phytochrome B (phyB) signaling (including during seedling de-etiolation) and gene expression. Mediates both entrainment to an environmental cycle and circadian rhythm sustainability under constant conditions. Controls flowering time. Necessary for light-induced expression of both CCA1 and LHY. Homodimer. Interacts with ELF3. Diffuse distribution. Targeted to nuclear bodies after interaction with ELF3 (PubMed:22327739). Follows a light-dependent circadian-regulated expression with a peak in the evening, about 12 hours after dawn. Induced in seedlings and roots by continuous far-red light (FRc) via the phyA signaling pathway and by continuous red light (Rc) via the phyB signaling pathway. This light-mediated induction is repressed by ELF3, CCA1 and LHY. Impaired in their ability to sense day length leading to early flowering in non-inductive photoperiods (probably through the misexpression of CO), and elongated hypocotyls and petioles in short days (SD). Attenuated light-regulated expression of CCA1 and LHY, central oscillator components. Transient output rhythms with highly variable period lengths before becoming arrhythmic. Reduced responsiveness to continuous red, but not continuous far-red light, suggesting a role in phyB signaling but not phyA signaling. Belongs to the EARLY FLOWERING 4 family.