domingo, 22 de mayo de 2011

Controlling LEDs Part 9 - Control types for LED products

Phase controlImage via Wikipedia
The following control technologies refer to the signal and wiring between the control on the wall and the fixture or lamp. LED retrofit lamps generally only use forward or reverse phase control technologies. LED fixtures may use any method, and it is independent of the driver type (constant current or constant voltage).

The compatibility of a dimmer with a particular LED fixture begins with making sure they both use the same control method. These control technologies are used in standalone applications and control systems as well as in wired and wireless lighting control systems. Controls that use phase control to control a lamp may also use a wireless technology to communicate between loads or within an entire home lighting control system.

Forward Phase Control:

Typically used for incandescent and magnetic low-voltage (MLV) light sources, this is the most common method of dimming control. The National Electrical Manufacturers Association (NEMA) estimates that there are approximately 150 million forward phase control dimmers installed residentially, and many of these are likely to control LED replacement lamps in the future.

Working well with forward phase control is critical to the success of LED bulbs because of the huge existing installed base. Unfortunately, these controls were never designed for LED lights and are not UL listed to operate LED lights, so the performance is hit or miss and in many cases will cause LEDs to flicker, drop out, pop on or not dim very low. These dimming controls may also require multiple lamps per control in order to meet the minimum load requirements of the control.

New forward phase control dimmers have recently entered the market that have been specially designed to reduce or eliminate the problems seen with controlling LED loads on existing incandescent dimmers. These dimmers are UL listed with specific LED loads, ensuring an acceptable application.

Reverse Phase Control:

Typically used to control electronic low-voltage (ELV) light sources, reverse phase control is best for capacitive loads such as LED drivers. While it does not have the installed base that incandescent dimmers have, this control type is often more successful at high performance LED dimming without flicker.
Reverse phase dimmers were designed for the lower power “electronic loads” of electronic low-voltage  transformers, so they tend to work better with the drivers required for LED loads.
Unfortunately, these controls nearly always require a neutral wire to power the internal electronics, and not every electrical back box has a neutral present. Installing reverse phase dimmers in older buildings may require that a neutral wire is pulled to the box. Furthermore, these types of controls are not as widely available in the marketplace and are generally more costly.

Three Wire Control: 

This standard fluorescent control type is used by dimmers that were created for fluorescent dimming. Three-wire controls have a separate line voltage wire that carries the phase control signal separate from the power wires.
Three-wire is more precise than forward or reverse and the control signal is much more immune to electrical noise. There are over 30 years of history in the industry of using 3-wire controls to dim fluorescent ballasts to 1% without flicker, drop out, or pop on. Of course, to get this performance, a third line voltage control wire must be pulled to the fixture.

0-10V Control:

This analog control standard has been used in energy management controls such as occupancy and daylight sensors and is now becoming popular with many LED products. This control type is isolated and considered low voltage class 2, enabling it to be safe to the touch and allowing for simplified wiring.
One of the benefits of 0-10V controls is that it is defined in the IEC standard number 60929 Annex E. Unfortunately, some manufacturers don’t follow this standard. This leads to drivers and lamps that claim to be 0-10V compatible but drop out or pop on, or that dim backwards with the lowest light at the top of the  control and the brightest light at the bottom. Some 0-10V products do not work at all with controls designed for 0-10V ballasts, which are the majority of installed 0-10V controls. Since the control signal is a small analog voltage, long wire runs can produce a significant drop in the signal level resulting in different light levels from different drivers controlled by the same control device.


The DALI digital standard originated in Europe for control of fluorescent ballasts, but is now commonplace in commercial buildings in the United States. DALI is also defined in IEC standard 60929 Annex E. It allows for digital control of individual fixtures, maximizing the user’s control and productivity. DALI provide addressing of individual fixtures and status feedback from the drivers. This makes it easy to digitally assign occupancy sensors, daylight sensors, time clocks, manual controls and other controls to one or many fixtures without complicated wiring. This opens up an entire suite of energy-saving and system-monitoring control schemes where the design and setup is all done within software, making designing with them simple.


Typically used in theatrical applications, DMX remains popular with RGB LED applications where multiple channels are necessary for individual color control. Some manufacturers are using DMX as the control type for white light in general illumination applications, which can often be complicated in terms of wiring, addressing, and interacting with other controls in the space.