How does LED Dimming Work?

Dimming LED Lamps

One of the advantages of LED lights is that depending on how they are configured, they can be dimmed. However, even LED lamps that say they designed to dim sometimes do not work with certain dimmers, resulting in some challenges.

 

Overall, it's always important to make sure to read the packaging or check with the manufacturer to make sure the LED you are using is designed to dim. You never want to use a non-dimming LED with a dimmer as it can greatly shorten the life of the lamp.

 

Here's a look at how dimming in LED lamps works and some options that are available.

 

Why Dim LEDs?

There are quite a few positive benefits that dimming an LED lamp can bring. First and foremost, being able to dim an LED lamp offers additional energy savings at about a 1:1 ratio. So if you can dim an LED lamp to 50%, that means it will only need to use about 50% of the energy it would normally need to illuminate. Plus dimming an LED lamp will allow you to possibly extend it's already long lifespan even further as there is less heat made and less stress on the lamp's components. Over time, that can add up to a lot of savings!

 

Another benefit of LED dimming is what it brings to the environment in terms of ambiance. Being able to dim an LED lamp gives you the flexibility to set the mood for whatever type of situation you are in. This can be very important in business and office environments where owners and managers want the ability to set the light brightness to the visual needs of their employees. And consumers also want the same ability they had with incandescent bulbs to make the light in their home what they want.

 

LED Dimming Issues

One potential issue with dimmable LEDs is that unlike traditional incandescent bulbs that almost always can dim down to about 1%, LED lamps have a much larger range -- anywhere from 5% to 20% -- that varies between manufacturers. That means you really have to do your research to make sure you're getting the appropriate dimming percentage you need for your project.

 

Additionally, even though an LED is dimmable, it may still have some issues. One known potential problem with dimming an LED is called "drop out" -- this is when as the LED is dimmed almost to its maximum percentage, it suddenly just completely turns off. A similar issue can also happen when you start to raise the brightness of the LED lamp from being dimmed -- it may suddenly "pop on" to its full illumination.

 

Other potential LED dimming problems can also be flickering -- either constant or sporadic -- and an issue called "dead travel," which is the amount you can change the control before the light itself also changes. For example, if you slide a dimmer almost half way before the light itself actually begins to dim, that would be explained as a 50% "dead travel" for that dimmer.

 

And another potential issue to keep in mind is what the dimming may do the LED driver. As we discussed in our article on LED drivers, LEDs require a driver to convert AC power into the DC power the LEDs need, and it keeps the power coming consistently, offering protection from power surges that could cause the LEDs to overheat and fail. Sometimes dimming an LED can cause the driver to lose efficiency, which could lead to it not doing its job well in protecting the LED lamp.

 

LED Dimming Options

There are two main in ways in which LEDs are dimmed -- Pulse-width modulation (PWM) dimming and constant current reduction (CCR) – and each type has its own pros and cons.

 

PWM Dimming

Pulse-width modulation (PWM) dimming works by turning the LED on and off at a very high speed. Although it actually ends up making the light flicker, it's so fast that the human eye doesn't notice. PWM works by using the exact amount of electrical current the LED requires, and quickly switches between that current amount and 0. So either the LED is running on its necessary amount of power, or it's off.

 

A benefit of PWM dimming is that is allows the LED to be on for less time, helping to lower its internal temperature and potentially adding to is lifespan. Another benefit is color temperature -- PWM dimming keeps LEDs running at their rated electrical current level, so the expected color temperature of an LED lamp does not change and stays constant through dimming.

 

Some possible drawbacks to PWM dimming is the potential for some noise generation from the lamp, and some flickering can occur if the appropriate PWM frequency is not used. Additionally, sometimes PWM drivers can generate electromagnetic interference (EMI), making them unsuitable for certain applications such as medical.

 

CCR Reduction

In constant current reduction (CCR) dimming -- also sometimes known as analog dimming -- as the electrical current that is needed to illuminate the LED lamp flows through it, the current itself is lowered to dim the lamp.

 

Again, CCR dimming can help increase the life of an LED lamp as a lower current equals lower heat generation, helping to decrease stress to the lamp's components. Additionally, CCR dimming does not result in any noise generation or flickering.

 

On the flipside, CCR dimming an sometimes have some issues with dimming LED lamps at very low current -- or deep dimming -- levels, and may also sometimes result in slightly changing the color of the emitted light as the lamp is dimmed.

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