LED Dimming Technology

Since LED lighting has become popular, one of the most common topics that I am asked about on a daily basis is dimming.  What used to be a fairly straight forward proposition dimming incandescent fixtures has been made more complicated by the fact that the new LED technology is very finicky about how it is dimmed.

The dimming methods that I see used the most with LEDs are reverse phase dimming (Electronic Low Voltage, or ELV), forward phase dimming (Magnetic Low Voltage, or MLV), and 0-10v.

Reverse phase dimming
In reverse phase dimming, each power line cycle is only energized for the initial part of the sine wave.

Forward phase dimming
In forward phase dimming, each power line cycle is only energized for the trailing part of the sine wave.

0-10 volt dimming.
In this method, the LED driver is monitoring for a control signal that ranges between 0 and 10 volts.  10 volts will usually be 0% dimming, or off.  0 volts will usually be 100% or full brightness.  This is so that in the event of a failure on the device sending the signal, the light defaults to fully on.

Advantages / Disadvantages
Reverse Phase
The advantaged to reverse phase are that it is designed as a semiconductor rather than a transistor, which allows it to be more efficient and can have a higher load to dim.  By controlling the off cycle of the sine wave, it reduces dimming "hum or buzz" like the forward phase can, but without the need of a choke.

A disadvantage to the technology that reverse phase uses, is that it can produce a lot of heat from controlling the dimming of the sine wave.

Forward Phase  
The advantages here are that forward phase is budget friendly, it is common, and has high quality chokes that will produce less dimming "hum or buzz."

One disadvantage is that while the hum or buzz should be quieter, it still may be present, which is a downfall of the technology.  Also, it may not perform well with electronic ballasts or dimmers due to the distorted nature of the waveform generated.  This can damage or destroy equipment that is not designed to work with this technology.

0-10v
The advantages to 0-10v dimming are that you can run the signal wire fairly long distances, and that for the most part, drivers are universally compatible with the 0-10v signal.  You can also mix lamp types, you can run 0-10v fluorescent and LED on the same signal.

The disadvantages are that over a long distance, the 0-10v signal suffers voltage drop, meaning that if your last fixture on the run is only receiving 8 volts, it will only come up to 80% where other lights are at 100%.  The other disadvantage is that there are still electricians who are unfamiliar with the technology and do not understand that they have to pull the additional control signal wire to each fixture.  This can be a problem if the job has been sheet rocked before they install the dimmer to test it.