How Does Dimmer Switch Work?
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Current
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An alternating current passes through the circuit connected to the bulb and dimmer switch. The alternating current alternates in polarity between negative and positive charges (it is a sine wave). Because of this alternation, there is a point where polarity is neutral and zero charge is going through the circuit. Voltage thus is variable based on the fluctuation of the sine wave.
Dimmer Parts and Function
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Inside a dimmer switch, there is a triode alternating current switch (triac). This is connected to two terminals, which are wired to two ends of the circuit. The circuit also contains a variable resistor that connects a gate. As the current flows through the dimmer switch, the variable resister controls the voltage on the gate. The amount of voltage determines the switching action of the gate. When there is a large enough voltage going through the gate (remember, the current is a sine wave and fluctuates), then electrons can move easily through the triac and the electricity is conducted through the dimmer switch. This is what allows the bulb to be on.
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The Dimmer as a Whole
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A dimmer switch essentially cuts the sine wave of the current into pieces. Every time the polarity of the current equals zero (as in each time the direction of the current changes), the voltage that passes through the gate is zero and the switch turns off the bulb. The voltage of the current eventually climbs back up as the sine wave fluctuates. The setting on the dimmer switch determines at what point in the sine-wave fluctuation the light circuit will be turned back on and the bulb will function again. A low setting means the gate will be open (nonconductive, leaving the circuit incomplete) for a longer period and the bulb thus is off for a longer time. A high setting means the gate will be open for a shorter period and the bulb will be off for a shorter time.
Perception
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Regardless of the setting on the dimmer switch, the opening and closing of the gate (and thus the circuit) occurs many times per second. It happens so fast that we do not perceive the individual starts and stops with the naked eye. We instead perceive the circuit change in terms of brightness. The more the gate is open (the lower the dimmer setting), the fewer times the bulb is turned back on and the dimmer the light appears. The more the gate is closed, the more times the bulb is turned on and the brighter the light appears.
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