Loading... Please wait...


Common Issues with LED Lamps and Dimming

Posted by

We often receive calls from clients stating that they have installed new LED bulbs into their commercial, institutional, or theatrical (non-residential) lighting control systems and they can no longer dim the LED bulbs properly.  Are you having issues dimming your LED lamps?  What are some of the items you should consider when installing LED lamps into your dimming system?  How can you test for LED lamp compatibility with your dimming system?  Why do forward phase and reverse phase dimming matter?  Here are some of our conversations around why your LED bulbs might not be integrating properly into your lighting system.  This is a compilation of a series of blogs on our other website, www.knightsoundandlighting.com. Knight Sound & Lighting has 2 websites, both www.goknight.com and www.knightsoundandlighting.com.


We have successfully replaced many incandescent systems with new LED lamps and have had tremendous success.  Why switch to LED lamps? The biggest reason is the amount of energy you save by using an LED lamp which can be about a 20 times (or larger) savings over an incandescent lamp or 6 times savings for an LED lamp versus a fluorescent lamp.

What is the advantage of LED lamps over fluorescent lamps? 

  • LED lamps can save 20 times the energy of incandescent lamps 6 times the energy of fluorescent lamps 
  • LED lamps produce less heat so your HVAC costs are lower
  • LED lamps are not considered hazardous materials (there is mercury in fluorescent lamps) 
  • LED lamps do not break nearly as easily as a fluorescent tube 
  • LED lamps longer life reduces maintenance staff time to change out the lamps (think here of less time on ladders, lifts, and scaffolding replacing lamps)


As many of you may have found out, not all LED lamps and/or LED lighting fixtures are created equal.  A common problem that we run into within our industry is when a customer wants to replace their existing incandescent lamps with new highly efficient LED lamps and/or LED lighting fixtures. When they change out all of their LED Lamps and/or LED lighting fixtures and then turn them on, they often find them flickering.  

There are many reasons why an LED lamp can flicker, but the most common cause is a lack of resistance in the lamp to allow the dimmer curve to work correctly. This is not a new issue; it’s been around for a long time, but is becoming more “noticeable” with the major increase in LED usage.  We first saw this issue when dimmable fluorescent lamps and/or dimmable lighting fixtures became popular several years ago. The same issue occurred at that time, because the fluorescent lamp does not have enough resistive load between the load and neutral wires (complete circuit).

Over the years, we have done many things to try to stop that flickering issue with the fluorescent lamps and now with the LED lamps. The biggest key is often to add resistance, but this does not always fix the problem.  Many dimming manufacturers and LED manufacturers are now working together to prevent this issue. However, since there are so many new LED lamp manufacturers, it is hard to achieve much consistency within the industry.


The quickest advice I can give you at this time is try out the LED Lamps and/or LED fixtures on one circuit, before you order a whole lot of LED lamps. I recommend taking a circuit with between 1-5 lamps on it to replace with the LED lamps and/or LED fixtures. If the LED lamps will work on this type of circuit, then odds are high that it will work on the rest of your circuits.

What are the LED manufacturers doing to correct this issue? As mentioned above, they are getting together with the dimming manufacturers and are working on solutions. A simple solution is for the LED lamp manufacturers to add a resistant circuit to each lamp, which helps with the dimming process.  In addition, the dimming manufacturers are coming out with many new types of dimmers, which help to address the need for very little resistance on the dimmer by either adding resistance to the load or using different types of dimming such as forward phase or amplitude dimming. However, if you already have dimmers, it hardly seems like a fair trade to replace your dimmers to install LED lamps and/or lighting fixtures.


What is the difference between traditional "Forward Phase" Dimming and newer "Reverse Phase" Dimming technology?  The distinction is important because of LED lamps and drivers (drivers are the electronics that run the LED lamps). The lack of resistance in LED Drivers can cause problems in the dimming of LED lamps.  How can a Reverse Phase Dimmer help to correct the issue of a lack of resistance in the LED lamps driver and electronics? The simple answer is the cycle of power and how it is applied with a Reverse Phase or ELV Dimmer. The diagram below shows both a Forward Phase (Triac based; Diagram A-on left) and a Reverse Phase (ELV based; Diagram B-on right) Dimmer Curve.

Forward Phase and Reverse Phase Dimming ImageNow that you have seen the images of the Forward Phase and Reverse Phase Dimmer Curve, what exactly are we looking at in the image? If you think left to right (just like in reading), when you look at the images, then the power is coming from the left edge and then is flowing out of the right edge.  In Image A (Forward Phase Dimming), you see that the power comes in from the left, but is suppressed or prevented from operating until it has gone through approximately 1/3 of the cycle (this is shown with the dots on the curve). Then the power comes in quickly from the crossover line (center horizontal line) and goes to the correct level.  Whereas on Image B (Reverse Phase Dimming), the power comes in normal through approximately 2/3 of the cycle’s wave and then is cut out or suppressed for the last 1/3 of the cycle’s wave.

Both Forward Phase Dimming and Reverse Phase Dimming provide the exact same amount of energy to the light fixture, which they are powering. The BIG difference is that with Reverse Phase Dimming, the electronics in a LED Driver and/or Fluorescent Ballast are powered FIRST and then the dimming occurs second. Physically, we can not see the difference in the two types of Dimming, but the LED Driver and/or the Fluorescent Ballast sure notices the difference and will respond VERY differently to the two types of Dimming Styles.

Almost all dimmers made in the world prior to the year 2010 were Forward Phase (Triac Based) Dimmers. That is why a lot of time, the LED Drivers and/or Fluorescent Ballast do not work well when connected to existing dimmers. Since there are so many Forward Phase Dimmers around the world, the leading LED manufacturers are working with the Dimmer Manufacturers to try to make their LED Lamps/Drivers work with Forward Phase Dimmers. However, since LED Lamps/Drivers is a growth industry and it seems like everyone is getting into the industry, there is a lot of room for error in the design of the LED lamps and/or drivers to work with Forward Phase Dimmers. 

When you are choosing an LED Lamp, LED Driver, Fluorescent Lamp, and/or Fluorescent Ballast make sure that is Forward Phase Dimming Capable.  This is really important if you have existing dimmers.

One note is that the Fluorescent lamp and ballast manufacturers have already worked out a lot of these issues and the vast majority of Fluorescent lamps and ballast that say “dimming capable” are Forward Phase Dimming Capable.

If you are doing new projects and can select both the LED Lamps and Drivers for your project, then you should take some time and plan accordingly. Yes, you can purchase Reverse Phase Dimmers from several lighting manufacturers, which will work very well with dimming capable LED Lamps and Drivers. Again, you must make sure that the LED Lamps and/or Drivers are dimmable, even with a Reverse Phase Dimmer. Several LED Lamps and Drivers are NOT dimmable and will not work, whether you use a Forward or Reverse Phase Dimmer.

Hopefully, this very basic discussion of issues around LED lamps and dimming will provide you with some more context when planning your next lighting project.  Please keep in mind that Knight Sound & Lighting can help you with your project planning, bill of materials, or technical issues when you are working on dimming and control options for your facility.  Please call us at 1-866-457-5937 if you would like to speak to a lighting technician about your system.

Source:  Interview with Mark A. Knight, CEO of Knight Sound & Lighting

Additional Resources:

View Comments

Leviton Remembrance Stations are discontinued from new production but existing units can be repaired to full functionality

Leviton Remembrance Stations (RMB81) and Colortran Remembrance (CTP-8) stations are discontinued from new production.  However, we can repair your existing Leviton Remembrance stations and bring them back to full functionality!Leviton Manufacturing has discontinued the new production of Leviton Remembrance Stations.  These are Leviton RMB81 and Colortran CTP-8 model numbers and include both analog Remembrance stations [...]

Read More »

​Do I HAVE to replace my Colortran ENR (aka Leviton or NSI Topaz) system?

No! –The Colortran ENR (aka Leviton or NSI Topaz) system can operate efficiently for many more years!As a technician in the field, I hear this question all the time and my response is simply, “NO!” Knight Sound & Lighting has been working with this product line for over 25 years and continues to keep thousands of Colortran ENR systems [...]

Read More »

Knight Sound & Lighting can repair the discontinued ETC SmartFade lighting consoles!

Extend the life of your ETC SmartFade lighting consoles with a factory repair! ETC has announced the discontinuation of the SmartFade lighting console series effective June 1, 2017.  This means that ETC will no longer manufacture new SmartFade lighting consoles after that date.  The SmartFade family of control consoles includes the SF1248, SF2496, SF1296, SFML, and [...]

Read More »

Why will my new lighting console not gain control of my existing Colortran ENR of Leviton Topaz dimming system?

Why will my new lighting console not gain control of my existing Colortran ENR of Leviton Topaz dimming system?  You need a Leviton IF501 converter! This blog is designed to help the end users of Colortran ENR and Leviton Topaz Dimmer Rack Systems understand how their dimmer racks receive their commands to turn on, off, and dim [...]

Read More »

How to Fix a MicroLite card with bad LED indicator lights

How do you fix a MicroLite card with non-functional LED indicator lights?  On a MicroLite ROM card (also known as the "black handled card") the top LED indicator light should be flashing and the bottom LED indicator light should be on at all times.  When the LED indicator lights are in this state, then the [...]

Read More »

Colortran ENR dimmer rack with airflow error

Do you have a Colortran ENR dimmer rack that is having airflow issues?If you have a Colortran ENR or Leviton Topaz dimming rack, then you might have seen this before. If you look at the bottom of the dimmer rack near the control module, or "brains" of the system, WHILE THE SYSTEM IS ON, then you might [...]

Read More »

Microlite (Musco) Lighting Controls Retrofit - Heinz Field Case Study

Musco Lighting’s Microlite 1000 Relay Control System at Heinz Field Retrofitted with Intelligent Lighting Controls (ILC) LightLEEDer Retrofit Control System by Knight Sound & Lighting August 2016; Cuyahoga Falls, OH – Knight Sound & Lighting announced it has recently completed a lighting controls retrofit for PSSI Stadium Corp’s Heinz Field Stadium, home of the NFL Pittsburgh [...]

Read More »

Ways to reduce sound system noise to other tenants in a shared commercial space

Question:  We are an exercise studio in a commercial space with another tenant right next door to us. The tenant next door is complaining our music is too loud and they can hear the "thump thump" of the bass through our shared wall. Is this an issue your company may be able to help with? Thanks [...]

Read More »

MicroLite Relay System User Manuals and Programming Manuals

Are you looking for a MicroLite relay system User Manual or MicroLite Programming Manual?    Knight Sound & Lighting - www.goknight.com - now has FREE Microlite User Manuals and MicroLite Programming Manuals available for download. If you don't see the user manual that you need, then please call Knight Sound & Lighting at 1-866-457-5937 [...]

Read More »


Recent Updates

Sign up to our newsletter

Connect with us: Facebook Twitter