A dimming system is composed of a dimmer having switchable power modes and at least one lighting device. When the dimmer is in a non-dimming bypass mode, an input power is directly transmitted to the at least one lighting device with the dimmer being bypassed so that the circuit in the dimmer consumes no power. When the dimmer is in a dimming mode, an output selector of the dimmer outputs a dimming output power having a dimming command therein to each one of the at least one lighting device for each lighting device to decode the dimming command embedded in the dimming output power and perform a dimming operation according to the dimming command. As the dimming operation lasts briefly, the power consumed by the dimmer is extremely small. Accordingly, no heat dissipation issue arises and the present invention is applicable to all sorts of high power lighting devices.