Dimming LED Lamps and Luminaires

By Daniel Mozey, LC, MIES

For decades, dimming residential and commercial lighting was fairly straight forward – just match the total wattage to be dimmed with the wattage capacity of the dimmer.  The rise of the LED has changed this simple formula to one that requires more thought and preparation.  It’s not complicated, but understanding the basics will help avoid dimming issues. Before ordering luminaires and dimming products for your project, thoroughly research and understand the dimmers you intend to use.  The following is a brief overview of the technology and best practices to help your project go smoothly. 

Dimming & Control Schemes

While there are a number of different dimming protocols, it’s possible to separate them into four basic groups: Legacy Dimming, 0-10V Dimming, Dedicated Data Line Control, and Networked Lighting Control.

Legacy Dimming  would include all TRIAC and ELV dimmers. These dimmers are sometimes referred to as “phase dimmers.” Originally for use with incandescent lamps and luminaires, these basic dimmers have existed for a long time and have been modified over the years to work with LED lamps and luminaires. These phase style dimmers modulate the existing 120VAC line going to the luminaire to provide dimming. The driver must interpret the drop in energy with an equal drop in light output. In most situations, LED Rated ELV dimmers can do an adequate job for typical household applications.

0-10V Dimming  uses a dedicated Class-2 low-voltage cable to send a 0-10 volt dimming signal from the wall dimmer to the driver. The luminaire still has a 120V line going to the dimmer as well. The big advantage of 0-10V Dimming over TRIAC/ELV is that there is excellent compatibility between the various 0-10V dimmers and 0-10V rated luminaires, and that the dimmer’s performance is very smooth.

Examples of Dedicated Data Line Control are DALI and DMX. In both cases the luminaires can be grouped and controlled by computers running dedicated software. These two dimming protocols do use a “network” to control luminaires, but they are a dedicated closed network and do not directly hook up to the building’s computer network. DALI uses a simple 2-wire data cable, aka data bus, to communicate with the luminaires. Each luminaire has an address and can be controlled individually or in user assigned groups. If so outfitted, luminaires with DALI drivers can also send information back to the control software. DALI is for commercial building applications and can be integrated into building management systems. DMX was developed by the entertainment industry and uses either 3 or 5-wire data cables, typically with an XLR style termination. When you see a music concert or theatrical show, the dozens of theatrical lights are almost certainly being controlled by a DMX system. Besides theatrical, DMX can be used to dim auditorium lighting. In many ways DMX functions similar to DALI, but is best suited for entertainment venues. To address ever more capable and complex theatrical lighting, DMX over Ethernet was developed to allow significantly more communication channels.

Networked Lighting Control  is relatively new to the commercial lighting market. Known as Power Over Ethernet Lighting, or PoE, this recent development uses the building’s own data network to exchange information and power the luminaires.

Common Types of Wall Dimmers

There are four common wall dimmer types:  LED Rated Dimmers, LED+ELV Rated Dimmers, 0-10V dimmers, and DALI Dimmers.

Standard LED Rated wall dimmers use the existing 120V wiring to dim the luminaire.  Typically, these dimmers use a method of dimming called Forward Phase which works well with LED lamps. While these standard type of LED Rated dimmers work with most LED lamps, they often have incompatibility issues with the drivers found inside LED luminaires.

Another dimming option for LED luminaires is the LED+ELV Rated wall dimmer. These also use the existing 120V wiring to dim the luminaire and typically offer Reverse Phase and Forward Phase dimming.  The electronics in these type of dimmers are much more flexible in how they match up to the variety of LED drivers found in luminaires. 

If the option is available for your LED luminaire, the best choice of dimmer is the 0-10V type. 0-10V dimmers can offer greatly improved dimming performance, are simple to use, and are a top choice for residential and commercial dimming. It’s important to remember that 0-10V dimmers do not work with LED lamps (aka LED light bulbs).

DALI dimming, although not used much in the U.S., is very common in the rest of the world.  DALI is more complex than 0-10V, but offers excellent performance. 0-10V dimmers and DALI dimmers completely avoid driver incompatibility issues and load limitations, but do require additional low-voltage wiring between the luminaire and dimmer.

Selecting a Wall Dimmer

If you plan on dimming, use LED lamps/luminaires that specifically indicate that they work with dimmers.  Likewise, only use dimmers that are designed to work with LED luminaires.  If you find yourself upgrading a home to LED, then make sure to replace the old dimmers with new ones rated for use with LED.  For commercial projects, electrical wall switches and remoted relays should be chosen to have extra capacity to handle the brief Inrush surge. (For further information regarding Inrush, see our article on the QuantaLight website.)

When purchasing a wall dimmer, reading the outside box of a dimmer can be misleading. A wall dimmer that says it works with LED does not necessarily mean it will work with LED luminaires. Much of the confusion is from how dimmer manufacturers label different types of wall dimmers.  For example, the following is a table of their terminology:

WALL DIMMER TERM = MEANING

LED = LED Lamps  (but not LED Luminaires or LED Drivers)

ELV = Electronic Low Voltage  (meaning 120V input and 12VAC or 24VAC out; a holdover from the late 1990’s when ELV was used to power halogen MR16’s)

Electronic Solid State Transformer = LED Driver and/or ELV  (the meaning seems to vary)

Dimmable LED with Integrated Driver = LED Driver / LED Luminaire

0-10V = 0-10 Volt Dimming

Standard (non-LED) TRIAC and ELV dimmers are common because they are relatively cheap and use the existing wiring. Unfortunately, standard TRIAC and ELV dimmers most often do not work with LED luminaires. This is due to the inherent complexity in the design of dimmers and LED drivers. Don’t be surprised if a standard TRIAC or ELV dimmer causes flickers, gets hot, or simply does not work.

There are different types of LED approved dimmers.  Dimmable LED lamps typically work with any LED approved wall dimmer, on the other hand, many LED luminaires are offered with different drivers to accommodate different types of dimming schemes, so always check which type of dimmer your specific LED luminaire is designed to work with.

Using LED Dimmers

When using an LED or LED+ELV wall dimmer it is important to understand the steady-state load limitations of your dimmer. A LED or LED+ELV wall dimmer’s LED load rating is typically 60% – 75% lower than the published incandescent load rating.  With a remodel project, when upgrading from old incandescent to new LED, keep in mind that when using these dimmers you may not be able to dim all the LED fixtures on the existing single circuit. Again, check the total load you wish to dim. To prevent problems, always read the specifications and instructions of the dimmer you intend to use.

Proper setup and wiring of a LED+ELV Rated wall dimmer is important, so always carefully read the specification sheets and directions. Ideally, before the LED luminaires are installed, the dimming performance should be tested.  Lamps usually work fine with Forward Phase dimming. On the other hand, LED luminaires typically work best with Reverse Phase.  If your dimmer has selectable phase, and you have LED luminaires, try the Reverse Phase setting first.  If that does not dim properly, then try Forward Phase.  (See the dimmer’s instructions for details on changing settings.)  Some dimmers have an “auto phase” selection setting.  Also, how the dimmer is wired can affect performance, so see the dimmer’s wiring diagrams.  For Reverse Phase dimming to work properly with ELV, the dimmer will usually require a Neutral connection.

LED luminaires, as well as other electronic equipment, exhibit a condition called Inrush.  For residential homes this is rarely a problem, but Inrush can be a problem when there are lots of luminaires on one circuit such as found in commercial applications. The momentary Inrush current is much higher than the rated steady state current of the luminaire’s driver. Depending on total circuit load, to prevent nuisance circuit breaker tripping you may need to de-rate the total load on each circuit.  For commercial projects, heavy duty wall switches are also recommended. Work with your electrician to calculate the correct load of wall switches and circuit breakers to accommodate the momentary Inrush.

Not all LED+ELV wall dimmers are the same. Higher grade LED+ELV dimmers have better circuitry and can offer features such as “selectable phase.” Being able to change the “phase” of the dimmer can greatly increase the odds that your dimmer will work smoothly with the LED luminaire. It’s best to purchase from established high quality brands. Again, before purchasing your luminaires and dimmers always do research on the dimmer company’s website, read their knowledge articles, and read all directions and specifications. If you are remodeling, work with your electrician to understand your existing wiring and whether or not you will need to add circuits.

For the best performance, new commercial and new home builds should opt for 0-10V dimming. Remodel projects should also consider 0-10V dimming. (Keep in mind that, in addition to the 120V lines, a 0-10V dimming system does require low voltage lines going from the dimmer to each luminaire.) Less common and more costly are DALI and DMX. A DALI based dimming system is an option for commercial properties when more complex control of lighting is desired. DMX based dimming can often be found in entertainment venues. All three of these dimming options – 0-10V, DALI, and DMX – require “Class 2”  low-voltage wiring or a data line, but the dimming performance is excellent.

Following these basic suggestions should help you avoid dimmer related issues.  For a deeper and more technical discussion on dimming take a look at the following article link:  Deep Dive in Dimming 

Luminaire Connectivity and Emerging Schemes

DALI dimming was first developed in Europe in the early 1990’s as way to integrate lighting control into building automation systems. Besides offering good dimming performance, the strength of DALI was that it was capable of two-way communication. A DALI luminaire could, depending on its features, send back data on its performance. Each DALI capable lighting ballast/driver is individually addressable so that one fixture, or multiple fixtures in a Zone, could be controlled by a DALI wall dimmer or central computer. Dedicated 2-conductor DALI data cables are used to interconnect the control computers, dimmers, and luminaires. By the early 2000’s the first DALI systems were being rolled out in commercial buildings. While DALI was embraced by most of the world, installations in the U.S. have been much lower.

More recently a new dimming and connectivity protocol has emerged. It’s called PoE Lighting. With the rise of LED luminaires and their low energy draw it is now possible to power some LED luminaires with low voltage wiring (with a LED driver designed for this application). For commercial buildings PoE is functionally similar to DALI, in that it can send and receive information from the luminaire, and can be integrated into building software. The big difference is that instead of a dedicated closed network like DALI, PoE devices use the buildings internal communications network and in many cases PoE can also eliminate the 120VAC power lines going to the luminaires. By using CAT6 data lines which are DC powered, PoE can provide up to 53 watts of energy to a luminaire. PoE LED luminaires simply connect to the building’s data network, and like other PoE devices such as occupancy and temperature sensors, they use the network for both communications and operating power.

Much like other innovations – such as Sony’s Betamax™ – only time will tell if PoE Lighting becomes widely adopted. Currently there are limitations due to the limited number of LED drivers available. Another potential issue is the limited power available through the CAT6 wiring, and because of the small conductor size, the losses due to cable run length. Further, the longevity of the RJ45 terminations suppling the power to the luminaires is a concern. Yes, the contacts within an RJ45 jack are “gold plated,” but their contact area is really small and their physical contact pressure is low. Will these connections survive the heat, humidity, and high current draw over many years? How about those flimsy plastic tabs found on the RJ45 connectors? If the plastic tab breaks or is weak the contact pressure will be inadequate or worse, slip out. What happens if the network goes down? What happens if the building management software is hacked? PoE Lighting is a neat idea, and perhaps these concerns will be worked out. For now, if you are considering PoE for your project, make sure you ask lots of questions. For large buildings, the ability to control luminaires and monitor their use through a PoE system integrated into a building management platform is certainly appealing.

Copyright 2019; QuantaLight Inc.