Lighting Controls: Dimming 101

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We can all likely agree that being able to dim the lights to create a mood is a great feature. But how does dimming work? And why do we sometimes encounter dimming issues with LEDs?

This article aims to answer those questions and more.

Primer on Dimming

Let’s talk about how dimmers work. When a light switch is “on,” it sends electricity (in the form of alternating current “AC”) along the wire to your light fixtures. When it’s “off,” it won’t pass along any current.

We don’t want to get too technical, but it’s worth noting that AC power frequently reverses direction (hence the name “alternating current”). This is important, because when we talk about AC power, we count the cycles, which look like a wave. When we use a dimmer, we alter that cycle or wave.

A modern dimmer will cut a portion of the AC wave. The more it cuts, the darker the source will appear to our eye. This is where energy savings come into play. The cutting of the AC wave is what saves energy.

  • Fun fact: Did you know that when you dim a light fixture, the light is flickering so fast that you cannot see the flicker? It’s true!

Why the Correct Dimmer Matters

Have you ever plugged in a new LED lamp and turned it on with your dimmer, only to discover that the fixture flickers or hums? It probably isn’t a defective fixture the dimmer is the likely culprit.

Not all lighting, especially LED lighting, can be dimmed the same way.

When an incompatible dimmer and fixture are used, problems can occur. Think buzzing, flickering, or the light not turning on at all.


Types of Dimming

Remember: a modern dimmer cuts portions of the AC wave. So we have different types of dimmers based on how they cut that waveform.

Incandescent Dimming

Often called TRIAC dimming (you might see this on an LED lamp lighting facts label; this type of dimming refers to typical 120V incandescent dimming). When dimming incandescent lamps, dimming is smooth and natural. This type of dimming is considered “forward phase,” because it cuts or modifies the front half of the AC wave.

You don’t typically use this type of dimmer with LED lighting, though there are some exceptions, such as LED replacement bulbs built specifically for existing fixtures.


MLV Dimming, also known as Magnetic Low Voltage

Do you have a track lighting system or maybe some kitchen pendants that use halogen lamps? You might have a low-voltage system, which uses a transformer to modify the amount of power going to the fixture.

  • Note: Two types of transformers modify current for low-voltage fixtures: magnetic and electronic. We’re going to address magnetic first. How can you tell what kind of low-voltage lighting system you have? Check the labels on your transformers.

MLV dimming modifies the same “side” of the wave (forward phase control). Use an MLV dimmer if you have a low-voltage lighting system that has an MLV transformer.


ELV Dimming, a.k.a. Electronic Low Voltage

ELV has become more popular in recent years. ELV is another dimming protocol that works with electronic transformers in low-voltage lighting.

The opposite of MLV dimming, ELV dimmers modify the back half of an AC wave. Electrically, this protocol offers some benefits over MLV, such as smoother turn-on. We have seen a lot more LED fixtures working on ELV transformers, hence the recent popularity of this type of dimmer.

Joe Radio Ra

Tips for Choosing the Right Dimmer

  • Check the lighting facts label. This shows important information about the LED bulb or fixture, as well as what kind of dimmer you should install with the fixture.
  • Choose a reputable dimmer manufacturer. When dimming LED sources, LED-based dimmers can get expensive fast. Make sure you choose a dimmer manufacturer like Lutron Electronics or Crestron, who have proven track records with dimming.
    • Pro tip: Some manufacturers test their products with light fixtures. These dimmer manufactures offer compatibility paperwork as well, proving that they can correctly dim that particular fixture.
    • Discuss options with a lighting expert. Our consultants can help you make sure that the lighting you have in mind is compatible with what you currently have in place or are looking to purchase.
    • Download our LED buying guide. This free resource has more information on dimming, what to consider when shopping for LEDs, and more.

Do you have questions? Get in touch. Our lighting experts would be happy to assist you.


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