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Facts About Dimmers Switches

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Common questions are answered about dimmer switches that control your light fixtures.

Dimmer switches are an effective means to for saving energy and extending bulb life. Along with the practical benefits of placing a light fixture on a dimmer switch, most people utilize dimmers to create visual effects and ambience in a room.

Dimming Bulbs

1. Incandescent

2. Halogen

The most common dimmers will control both incandescent and halogen bulbs and lamps.

3. Fluorescent - fluorescent light bulbs require a ballast to turn them "ON". Most fluorescent light fixture ballasts will not work with dimmers. However, there are ballasts that are designed specifically to be dimmed. It will state on the ballast if it is a "dimmable" ballast. If you do have a dimmable ballast in a fluorescent fixture that you wish to control with a dimmer you must purchase a dimmer that is specifically rated for dimming fluorescent fixture ballasts.

4. Compact Fluorescent Light Bulbs (CFL) – These bulbs are basically fluorescent light bulbs made to replace standard incandescent bulbs that come in similar shapes and sizes of incandescent bulbs. There are dimmable CFL bulbs but there are typically only dimmable down to about 50 to 75% of their original power consumption. This is due to the fact that an arc must be created and maintained inside the bulb to produce light and below a certain level, the arc will not stay on and flickering and shortened bulb life will result.

A dimmable CFL

Typical Dimmer Switch Diagram

Common Questions

Can you have more than one dimmer in an electrical box?

More than one dimmer can usually be mounted in an electrical box. However, it should be noted that this usually decreases the wattage rating of each of the dimmers within the common electrical box. Installing multiple dimmers in an electrical box is referred to as “ganging.” Check the manufacturer's specifications for their rules on ganged dimmers.

Do dimmer switches save energy?

Yes, dimmer switches lower the light output by using a transistor like device called a TRIAC to switch the electricity on and off very rapidly,120 times each second. A typical modern dimmer switch is more than 99 percent efficient. Less than 1 watt is wasted by controlling every 100 Watts of light.

See the table below

Do dimmer switches extend the life of bulbs and lamps?

Yes. The table below how the life of an average bulb can be extended.

While this table is for incandescent lamps, halogen lamps show similar extended life characteristics.

Should my dimmer switch be warm?

Electronic dimmers dissipate heat. The closer the dimmer is to its specified full load, the warmer it will feel. As long as the load (wattage) that the dimmer is controlling is within its specifications, the dimmer will function properly. A good dimmer switch dissipate less than 2% of the energy consumed in heat, but even this small amount of heat is one of the reasons that the dimmer loads are lowered when ganged in the same electrical box.

Is it normal for lamps to buzz or hum when a dimmer is used?

Humming and buzzing is not uncommon and is usually caused by the lamp filament vibrating. The buzzing is most noticeable around the 50% level. There are four things you can do in an attempt to remove or reduce the buzzing noise.

1. Use bulbs that are designated "Rough Service".

2. Use a bulb that is physically smaller than the current bulb that buzzes.

3. Use a lower wattage bulb.

4. Some manufactures supply a device known as a lamp de-buzzing coil (LDC) which is installed in the circuit where the buzzing lamp is operating.

Are other electronic devices affected by a dimmer switch?

High quality dimmers will produce less “noise” in your electrical system. You may hear some static or buzzing noise on radios, especially in the AM frequency, and other communication devices. The buzzing noise is caused by radio frequency interference (RFI) generated by the dimmer. The quality dimmers have electronic circuitry within them that suppresses RFI, but even a high quality dimmer can create buzzing noises under certain circumstances.

There are a few fixes that can be tried to eliminate or reduce the buzzing noise

1. Move the affected communications device farther away from the dimmer, at least 6'.

2. Plug the affected device into a different circuit, that is not the same circuit as the dimmer is on.

3. Add a power-line filter to the device that is buzzing.

4. Contact the manufacturer for alternative solutions.

Can a dimmer switch be used with a 3-way or 4-way switch?

Yes you can use a dimmer switch that is designed for 3-way or 4-way switch applications.

Can a dimmer switch be mounted horizontally?

Refer to the manufacturer's specifications but most dimmer switches are designed to work in a vertical mounting position only.

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Daniel Snyder

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