For several years, I have been seeing a new hole in the theoretically 100-percent-complete electrical drawings we are provided for bidding. Within the last year, the problem has gotten bigger, driven by increasingly strict energy-usage requirements. The problem is light-emitting diode (LED) controls and dimming. Many engineers are simply not addressing the issue. While the LED fixtures are in the fixture schedules and on the plans, the controls are not. For the most part, on-off controls, including standard switching, motion sensors and relay panels, have not changed. However, if dimming or color controls are required, they often become the estimator’s problem.

My first time

The first time I had to deal with this was on a hard bid for a retail center. The fixture schedule clearly showed that some LED fixtures had red, green and blue (RGB) LED lamps. 

After completing the takeoff, I became suspicious there was a problem because no controls or control wiring were shown for the colored lamps. If all three colors were simply to be turned on and off, what was the point of using RGB lamps? A quick trip to the Internet provided the answers. The fixtures required a proprietary control panel and preassembled cables that carried both power and control signals to the fixtures. This would have been a big miss in 
the estimate.

I have estimated many jobs with RGB or dimming LEDs since then, and all of them had either the RGB and dimming controls shown incorrectly—or on most occasions, not shown at all. Because of this, I have added a new procedure to our estimating flow charts. I now require the specifications and installation instructions for all RGB and dimming LED fixtures be studied and understood before completing the estimate.

Types of dimming and controls

Just to keep things clear, let’s go over all of the current dimming methods. The first is called 2-wire, forward-phase dimming (aka, leading-edge, triac and SCR dimming). These dimmers have been around a long time and have been used primarily for incandescent lamps. They can still be used with some electronic low-voltage (ELV) transformers and LED drivers. The wiring required for this system is simply the same hot and neutral needed for a regular switch.

Next is 2-wire, reverse-phase dimming (aka, ELV, trailing-edge and reverse-phase). These dimmers were created to control ELV transformers used for 12-volt (V) MR16 lamps. They can also be used to control some LED lamps. ELV dimmers also require only a hot and a neutral wire.

Even though it requires an extra wire, Lutron Electronic Co.’s Hi-Lume 3-wire dimming system has become popular because of its ability to smoothly dim LEDs down to 1 percent. The system also allows for driver remote installation. This system requires a dimmed hot, a switched hot and a neutral wire.

Four-wire dimming (aka, 0–10V, 4-wire dimming and low-voltage dimming) has been around for years for fluorescent lighting, occupancy and daylight sensing systems, and it is becoming a standard for LED dimming. Lately, I have even seen projects that call for all LED fixtures to have 0–10V dimming drivers, regardless of whether they are dimmed. The wiring for these drivers includes two standard 600V wires for the switch leg and neutral and two low-voltage wires for the 0–10V signal. Several of the manufacturers I spoke to prefer a No. 16 stranded wire for the low-voltage signal. There is a limit on the amperage available from the dimmer, so you will need to calculate the number of dimming drivers that can be attached to one dimmer. There is also a limit on the length of the low-voltage wires because voltage drop can be a problem.

Also worth a mention, because they do not require wiring, wireless dimming systems are available from several manufacturers.

Finally, there are a number of digital control systems that can address LED fixtures, including digital multiplex (DMX) and digital addressable lighting interface (DALI). DMX was the system used in the retail center I mentioned before, and it required a special cable that carried both the power and the control signals. DMX systems can also be configured with separate power and control wiring. I have also bid a number of projects that used the DALI system for lighting control. The DALI protocol requires all devices involved with lighting and control to have a DALI interface, including dimmers, ballasts, drivers, daylight and motion sensors. All of the devices are then interconnected on a control network. The exact wiring for each digital control system can vary, so ensure you research the requirements for every control system you bid on.