In telecommunication, in the modulation of a carrier, a significant condition is one of the values of the signal parameter chosen to represent information. A significant condition could be an electrical current (voltage, or power level), an optical power level, a phase value, or a particular frequency or wavelength. The duration of a significant condition is the time interval between successive significant instants. A change from one significant condition to another is called a signal transition. Information can be transmitted either during the given time interval, or encoded as the presence or absence of a change in the received signal.