  We argue that transient systems with luminosity between novae and supernovae
(SNe) are powered by gravitational energy of mass accreted onto, or a companion
merges with, a main-sequence star. These transient events are termed
Intermediate-Luminosity Optical Transients (ILOTs; other terms in use are
Intermediate-Luminosity Red Transients and Red Novae). We show that despite the
wide range of 10^{45}-10^{50} erg, the typical energy released by ILOTs can be
expressed as a function of fundamental variables: the planck constant, speed of
light, gravitational constant, electron mass, neutron mass, and ignition
temperature of hydrogen. This expression explains why ILOTs are located between
SNe and novae with respect to their total energy. We also put an upper limit on
the power (luminosity) of ILOTs, which explains their lower luminosity than
SNe.
