Otis Singleton
Dimmer switches are a clever way to control the brightness of a light, allowing you to set the mood or ambience in a room. But do they help you save on your electricity bill? The short answer is yes, dimming your lights will reduce power use. However, the amount of energy saved may not be as much as you think. This is because dimmers work by modulating the electricity given to the lamp over time, turning it on and off very rapidly, and this process generates heat, wasting some energy.
Characteristics and Values
| Characteristics | Values |
|---|---|
| Do dimmers reduce voltage? | Dimmers do not directly reduce voltage but increase resistance, which has the same effect as reducing voltage. |
| How do dimmers work? | Dimmers work by modulating the electricity given to the lamp over time. |
| Do dimmer switches save electricity? | Dimmer switches do save electricity but not in a 1:1 ratio. |
| Do dimmers produce heat? | Yes, dimmers produce heat. |
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What You'll Learn
Dimmer switches and electricity savings
Dimmer switches are often used to create a cosy atmosphere at home, but do they help save on electricity bills?
Modern dimmers use a TRIAC, a semiconductor switch that can handle alternating current, and a small microprocessor. The TRIAC reduces the amount of time the light is on by preventing electricity from flowing every time the voltage reaches 0. This results in the light turning on and off about 120 times per second, with the frequency of the on-off cycle increasing in newer dimmers. This rapid switching on and off creates the dimming effect.
The use of a dimmer switch does result in a reduction of power use. However, due to the circuitry in the dimmer, there is not a direct 1:1 energy saving. For example, dimming the light to 50% will not equate to a 50% reduction in electricity usage. Additionally, some energy is wasted as heat generated by the dimmer circuitry and the light bulb. The amount of wasted energy increases proportionally with the load. Therefore, it is recommended not to use dimmers if the light will be left on at maximum brightness most of the time.
Dimmer switches do not directly reduce the voltage. The voltage remains constant at about 230V (or 110V depending on the country). However, by interrupting the current flow, the dimmer effectively reduces the voltage across the light bulb. This can be observed when measuring the voltage with a multimeter, where a lower voltage is recorded when using a dimmer switch.
The use of dimmer switches with LED lights can result in greater electricity savings compared to traditional incandescent bulbs. In one example, an LED bulb drawing 10-13W at full brightness only consumed 2-3W when dimmed to roughly half as much light.
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How dimmer switches work
Dimmer switches are used to control the brightness of lighting by adjusting the amount of electrical energy supplied to a bulb. They do not reduce the voltage but work by modulating the electricity given to the lamp over time.
Dimmer switches typically use a semiconductor device called a triac. Mains electricity is constantly varying in a cycle that happens 50 to 60 times every second. The triac in a dimmer circuit stays off for the first part of a cycle and then turns on for the rest of the cycle, allowing only some portion of each cycle to reach the output. The smaller the portion, the dimmer the light. The potentiometer that you turn on the dimmer switch controls when the triac turns on, thus altering the proportion of each cycle that goes to the lamp.
Modern dimmers use a TRIAC and a small microprocessor. The TRIAC is a semiconductor switch that can handle alternating current and a wide range of currents. The dimmer works by modulating the electricity given to the lamp over time. A lamp that turns itself off and on for a millisecond uses about 50% of the energy of a lamp that is on all the time.
A dimmer switch "chops up" the sine wave of the fluctuating household alternating current (AC). It automatically shuts the light bulb circuit off every time the current reverses direction—that is, whenever there is zero voltage running through the circuit. This happens twice per cycle, or 120 times a second. It turns the light circuit back on when the voltage climbs back up to a certain level. This "turn-on value" is based on the position of the dimmer switch's knob or slider.
Old dimmers control voltage output by acting as a variable resistor in series with the light load. They cause a voltage drop and get hot in the process. Newer dimmers send out full voltage in pulses, sending fewer and fewer pulses as they go down. On an old filament bulb, the pulsing dims it even though the voltage is still full.
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Types of dimmer switches
Dimmer switches are an affordable, simple way to improve your home's lighting appeal and energy efficiency. They can be used with incandescent bulbs, halogen light bulbs, compact fluorescent light bulbs (CFLs), and some LED light bulbs.
There are several types of dimmer switches available, including:
- Leading-edge and trailing-edge dimmers: Trailing-edge dimmers are generally the best choice for LED lights due to their compatibility and smooth operation. However, some retrofit LED light bulbs can work with either type. Leading-edge dimmers have a higher minimum load, and the lower wattage of LED bulbs means they may not function correctly when paired with them.
- Plug-in light dimmers: These dimmers plug into wall outlets and are designed for use with lamps.
- Smart dimmers: These dimmers can be controlled via Wi-Fi, Mesh, or Bluetooth, allowing you to adjust your lights from your device. They are widely available for most lighting types, especially incandescent and LED.
- MLV and ELV dimmers: These dimmers use a transformer to reduce the voltage. MLV dimmers reduce a 120V AC current to 12 or 24V, which, when delivered to an incandescent or halogen bulb, produces less light.
- Standard incandescent dimmer switches: These dimmers introduce a resistor to the circuit, reducing the amount of current reaching the bulb.
- Halogen dimmers: These use a technique called "phase control" to switch the light circuit off and on very rapidly, about 120 times per second.
- Ballast dimmers: These dimmers are used with fluorescent lights and reduce the voltage that the ballast produces.
- Single-pole and three-way dimmers: A single-pole light switch controls only one circuit and is the most common type found in homes. A three-way dimmer switch can control multiple light fixtures independently.
- Push-button, toggle, and rocker light switches: A push-button light switch is a classic design that has enjoyed a style revival. A toggle light switch is the most common type, with a switch lever that protrudes out from the wall and toggles up and down. A rocker light switch has a flat design that sits almost flush against the wall and rocks back and forth to turn the lights on and off.
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Dimmer switch circuitry
Dimmer switches do not reduce voltage but instead reduce the brightness of bulbs by modulating the electricity given to the lamp over time. This is achieved by chopping off part of the voltage cycle or sine wave, which results in a lower voltage output.
A dimmer switch can be understood as a variable resistor in series with the light load. The dimmer switch causes a voltage drop across it, similar to a light bulb, and this causes the dimmer to get hot.
Modern dimmer switches use a TRIAC (Triode for Alternating Current) and a small microprocessor. A TRIAC is a semiconductor switch that can handle alternating current and a decent range of currents. It is used to switch on a connected load in response to an external DC trigger. In a dimmer switch, the TRIAC is used to regulate AC so that the output to the load can be reduced to any desired value.
TRIAC dimmer circuits generate a lot of RF disturbances, so an RC network is required to reduce these. The RC network consists of resistors and capacitors in parallel, which act as a low pass filter to reduce the RF disturbances.
Dimmer switches can be dangerous to work with as they are connected directly to the mains AC.
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Dimmer switch installation
Dimmer switches do not reduce voltage, but they do lower the brightness of a lamp by modulating the electricity supplied to it over time. This means that the lamp is turned on and off very rapidly, so it is on for a millisecond and off for a millisecond, using about 50% of the energy of a lamp that is on continuously.
Dimmer switches waste a lot of power and do not save energy. They are a variable resistor in series with the light load, and they cause a voltage drop across the load in the same way as a light bulb, using up some of the voltage and giving off heat.
To install a dimmer switch, first, turn off the power to the circuit at the main fuse box. You can test that the power is off by using a non-contact voltage tester near the wires where you will be working. Once you are sure the power is off, remove the existing light switch and disconnect the wires. Connect the dimmer switch wires to the appropriate wires in the wall box—typically, the black wire from the dimmer switch connects to the black wire from the wall, and the white wire from the dimmer switch connects to the white wire from the wall. Secure the dimmer switch to the wall box with the provided screws and attach the dimmer switch cover plate. Restore power to the circuit and test the dimmer switch to ensure it is working correctly.
It is important to note that dimmer switches are not suitable for all types of light bulbs, such as LED bulbs, which may require a minimum wattage to function correctly. Always check the compatibility of your light bulbs with a dimmer switch before installation.
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Frequently asked questions
Electrical dimmers do not reduce the voltage but rather interrupt the voltage in a certain way to produce a dimmed effect. Modern dimmers use a TRIAC, a semiconductor switch that can handle alternating current, to reduce the amount of time the light is on.
A TRIAC prevents electricity from flowing every time voltage reaches 0. This creates a waveform where the light is turning off and on 120 times per second. With every cycle, a small amount of power is saved.
Yes, modern LED bulbs that can be dimmed save a lot of power. On several bulbs, a 10-13W "bulb" dimmed down to roughly half as bright draws only 2-3 Watts.
Yes, dimmer switches get hot due to the inefficiency of the transistors inside. The higher the voltage and more current flowing through, the hotter the unit gets.
