Constant Power for LED units

What type of power do we need for LED lighting units?

What type of power do we need for our new LED lighting units and systems? And how much of it? And how do we get it? The answers to these questions are changing daily with all the new technology developed by stage lighting manufacturers across the board. Lighting units have better optics and use brighter lamps. LED technology is constantly improving along the lines of Haitz’s Law. Using this new gear requires some rethinking when mixing with traditional fixtures makes things even messier—even as we need more constant or clean power.

Do I need Clean Power?

Lighting gear with electronics inside requires non-dimmed power, or “constant power.” Some people call this clean power. Though “clean power” is usually what the sound department wants. Constant power works for us just fine. So what is this “constant power,” and why do we want it? For that matter, what is “not-constant power?”

What kind of Power do I have?

Power from the electric company comes into our facilities at a voltage between 100-240 Volts, and in some cases even higher. The power is transmitted with an Alternating Current, aka AC, with a sine wave pattern of either 50Hz or 60Hz (Hz stands for Hertz, which translates to Cycles per Second.) The standard for North America (all of the US and Canada) and much of South America is 110-120 Volts at 60Hz. Larger theaters will often also have electrical service at 208-240V AC. Most other countries and continents use 220-240 Volts at 50hz.

How Much Power do I Have?

Main Disconnect Circuit Breaker Amperage is the amount of power. Simply put, the more Amps used, the brighter the light is likely to be. Your theater will have a total amount of power that can be used overall. You can check your main fuse box to see what the main disconnect switch can handle. In the example shown here, we see a 200Amp switch. Check with your facilities manager to find out what the power limits are for your space.



How Much Power do I have at each Outlet?

20 Amp Circuit Breaker Most theaters in the US use lighting circuits rated at 20 amps. You can check your Amerage ratings at your dimmer rack or circuit breaker box. The small number on the breaker switch is its rating. This standard AC power is considered “constant” power, a steady 120V, 60Hz.



Royal Court Theatre Grandmaster

How do Resistance Dimmers work?

In theater lighting, we used to limit the power to the lamps via resistance dimmers. Thus, holding back 100% of the power from the lamp, full resistance equals the lamp is off, up to offering no resistance (0% resistance), which allows the power to flow freely, giving us a lamp at full brightness. Nowadays, we manipulate the sine wave instead.

How do Sine Wave Dimmers Work?

Current dimmers change the structure of the sine wave to dim our lamps more efficiently than resistance dimmers. The dashed line represents the full sine wave reaching 120Volts at 60hz (cycles per second). The solid line of this illustration represents a dimmer sending an adjusted pattern of the electrical energy sent to the lamps in our lighting units. The top and bottom sections of our standard sine wave are being cut nearly in half resulting in our lamp burning at approximately 50-60% of its potential full brightness. In other words, our light is “at 50.” The term for this particular pattern is called “forward phase dimming.” Other technologies include “reverse phase dimming” and “sine wave dimming.” All of these involve the manipulation of the sine wave in one way or another.

Even at full, a sine wave dimmer has a little chop to it. See the video below for a demonstration.

Half Sine Waves

Can I Park my Dimmers at Full?

Unfortunately for us, all of these flavors of sine wave manipulated dimming will negatively impact the switching power supplies within our moving and/or LED lighting units. Any device that contains electronics prefers a smooth sine wave—constant power. Unfortunately, dimmers parked at full are still limited in their ability to supply full power with a smooth sine wave continually. Thus, even if you never plan to dim a channel that an LED light is plugged into, the mere fact that the circuit is run through a dimmer is enough to make it dirty or non-constant and unusable for a whole host of fixtures.

What does a Dimmer Sine Wave look like?

I found this terrific video showing what a sine wave looks like on an ossiliscope.  

We have some choices to make to solve our power needs. Just like the bypass switch shown in the video, we need a way to bypass or replace the dimmer with a hardwired direct solution. The dimmer manufacturers are building some solutions, and some involve modifying your dimmers or circuits in house.

What is a Constant Power Module?

Dimmer manufacturers are making constant power modules that can swap out with existing dimmer modules. These constant power modules can be a simple circuit breaker switch controlled solely at the dimmer rack or an on/off relay module that can be controlled remotely via signals from your control board. Of course, those that wish to be able to reset electronic units without a trip to the dimmer room will prefer the switching relay module.

Constant Power Relay Module from ETC

Can I rewire my Dimmers?

Solutions created in-house have included bypassing the electronics within a dimmer module and wiring straight to the circuit breaker. This might be particularly advantageous for those theaters that have dimmer modules that are nonfunctional and/or in need of repair. (As with anything involving the words “wiring” and “circuit breaker,” please keep in mind that any act of that nature should only be done by fully trained, competent and authorized personnel.)

For the annual Stage Lighting Super Saturday workshop, held in New York City, manufacturers showing their equipment often request constant power. When theaters in which the workshop is held do not have constant power modules, Lite-Trol Services has come in and “strapped the dimmers.” In other words, Lite-Trol hardwired jumpers to safely bypass the sine-wave altering electronics inside the dimmer modules of our hosting theater. Without their assistance, we would need to rent power distribution boxes and tap into the building power to supply constant power to the manufacturers displaying their electronic equipment. Not to worry, the dimmers were restored afterward.

Unstrapped Dimmer

Dimmer with wires where they are supposed to be.

Strapped Dimmer

Two yellow connectors combined, bypassing the dimmer

A third option is to bypass the power to the grid completely and plug in fixtures to a standard building outlet in the wall.

I had the opportunity to design a production of Joseph and the Technicolor Dreamcoat in a large high school theater built in the 1970s. Over the stage were three pipes containing 40 feet of R40-type strip lights as downlights and covering the CYC. Of course, 90% of the lamps were burnt out. Renting MR16 strip lights for the CYC would have been an option, except that the existing strip lights were hardwired to the dimmers, and I had no way of plugging rental units in. My solution was to rent 40 feet worth of LED strip lights, daisy-chain them all together, and plug them into a single wall outlet. The power consumption of these LED strip lights is so low that I could plug all nine of them into a standard wall outlet at the back of the stage. For control, a single 250-foot DMX cable was run over the ceiling from the booth to the back wall.

During the planning phase of the design, I had to calculate how many strip lights I needed. My 40′ needed nine units to cover our backdrop/CYC. Could this work with just one outlet? Looking at the spec sheet for the LED strip lights, I figured out how many I could plug into the wall outlet by looking to see how many Amps each unit requires. Each strip needed 1.2 Amps, and our outlet (in this theater) is rated at 20 Amps. In theory, we could plug 16 of these into our 20 Amp circuit. Note that the manufacturer specifies daisy chaining no more than 11 together. My nine units had room to spare.

Row of Strip Lights

What Connectors Should I Use?

An almost guaranteed method of making sure that your expensive electronic lighting units are not accidentally plugged into a standard dimmer circuit is to use a different type of connector at the end of the power cable. For theaters that use traditional 2P&G stage pin connectors for their dimming circuit, using a round twist lock type connector for all devices wanting constant power is a terrific solution.

We have a 2P&G (2 Pins plus the Ground) used in many theaters. These are rugged connectors that can be laid flat on the floor. The twist lock has the benefit of being securely connected with a twist-to-lock action, hence the name. Another twist lock version is the PowerCon True1 connector, which is becoming popular on newer LED and automated lighting units. These are color-coded to show what goes with power in and power out. A google search revealed several new products designed to help keep it all straight using PowerCon connectors. Lex products make a new 20Amp “Breakout Box” to be used with Multi-Cable, and the version shown has six individual circuits. Imagine using this with those LED strip lights mentioned earlier. The strip lights can daisy chain eleven lights in a row in a circuit. With six circuits, we can have 66 strip lights on one multicable.

Cable runs, circuit plots, and power and cable management are all made easier with preplanning and paperwork. Using the lighting designer’s light plot allows the production electrician to figure out what type of power is needed where. This is yet another reason for the lighting designer to have the plot in the hands of the electricians as early as possible. Gone are the days of simply hanging all the lights and figuring out how to plug them in later.

What is 208V power?

This video teaches us about 208V and how it comes from using two phases of three-phase power.

In 2015 Stage Directions asked me to write about the power needed for LED and Automated lighting units. Any unit that has an internal power supply. The article was published in the May 5th, 2015 issue. Much of the above was used in the article above.