CPM Article: Modern Dimming - Choosing the Right Technology
by: David Martin Jacques

Copyright © 2006 by David Jacques

Published in the December, 2006 issue of Church Production Magazine
By: David Martin Jacques
For: Church Production Magazine

The music is gently softening from its loud crescendo, and in response you slowly pull down the faders to dim the lights. As the serene quiet washes over the congregation, you start hearing that annoying buzz. Where is it coming from? Is it the guitar amplifier? A short in the microphone cable? That old Leslie speaker? No, it’s probably noise emanating from the filaments of the lamps in your lighting fixtures.

Where does this filament noise come from? Chances are that your dimmers are creating it. SCR (Silicon Controlled Rectifier) dimmers have been around since the 1970’s, and although they have improved greatly with technology, they cannot escape the basic physical flaw of their design.

SCR dimmers work by varying the switch on point of the lamp current each half cycle. These dimmers slice the waveform in half, and using chokes, increase the rise time, and use the inertia of the filament to smooth out the switching change. This causes the filaments in the lamp to buzz (creating noise and shortening lamp life). In addition, the electronic spikes that occur in these dimmers create radio frequency interference. You hear the unfortunate results of this cross-interference through other electronics (like amplifiers and wireless devices). Although lighting equipment manufacturers have improved these negative artifacts with advanced technology and high-quality chokes, it is impossible to completely silence these dimmers.

In some of today’s extreme noise-sensitive environments such as opera houses, television studios, and houses of worship, modern SCR dimmers may just be too noisy. If you desire complete silence from your lighting system, sine wave dimming may be for you.

Unlike SCR’s, sine wave dimmers produce a pure sine wave output with variable amplitude to control lighting levels. Through the use of transistors to slice the mains into pulses, these dimmers vary the current using pulse-width modulation, average the result, and produce a continuous, variable amplitude smooth sine wave. This in turn eliminates the noise to the filament. In addition this technology lowers the operating cost as it uses less ‘reactive’ power (produced by harmonics in SCR dimmers), lowers the maintenance cost as lamps last longer, and eliminates radio cross-interference.

Sine wave dimming also allows you to dim almost any kind of load. This includes neon, HMI, LED, and even some motors. Try this with a conventional SCR dimmer and you may be in for an unfortunate surprise.

European theaters and opera houses have employed sine wave dimmers for several years, enjoying the benefits of the silent technology. And sine wave has now caught on in the US. Major manufacturers of theatrical dimmers offer various configurations of SCR and sine wave dimmers. ETC (Electronic Theatre Controls) offers various configurations of SCR and sine wave dimmers. Strand Lighting’s C21 dimmer racks allow the user to mix sine wave and conventional SCR dimmers in the same rack.

So is sine wave technology for you? It is important to recognize your needs as you may not require such quiet dimmers. Due to its added cost (approximately twice the cost of SCR); it may not make sense to upgrade. However, if you desire ultra-quiet dimmers, longer lamp life, and the ability to dim everything from Lekos to neon, then sine wave dimmers may be just the ticket.

Another crucial decision is the type of dimming distribution that would be appropriate for your house of worship. The days of being limited to placing dimmer racks in a closet are over. You now have a choice of centralized or distributed dimming.
Centralized dimming systems are situated in one central location. The dimmer racks are installed in this location with the power mains supplying voltage. High power circuits are run from the dimmers to the remote connector strip and plug box locations in the theatre. From these locations lighting fixtures and other loads are connected.
Distributed dimming is the new wave of control design. Instead of being located in a dimmer room, the dimmers are placed close to their fixtures and loads. These dimmers come in many designs depending on the need. They are completely self-contained and have internal protection devices including circuit breakers. Although the cost per dimmer may appear higher, distributed dimmers eliminate the need for high-capacity power circuits, plug boxes, and connector strips.
The major lighting equipment manufacturers offer several solutions for distributed dimming. ETC offers the SmartModule, the SmartBar, and soon the SineWave Power Module. The SmartBar is a remote dimmer module that is 6’ long and houses 4 – 600W dimmers. We are using 16 SmartBars in our small theatre on campus. This allows us to locate these dimmers almost anywhere in the theatre.

ETC is not the only company producing distributed-dimming products. Entertainment Technology, a Genlyte company, offers the IPS Dimmer Box and Dimmer Strip, as well as the Bak Pak Individual Dimmer. Strand Lighting offers a “CD80 Single” dimmer for remote locations, and Leviton has their DDS line of remote dimmers. Like ETC’s products, all you need to do is to run power and control cables to these dimmers.

Some dimmers are small enough to be located inside the actual lighting fixture. The ETC Revolution moving light comes with an internal dimmer, and the Vari*Lite VL1000 can be ordered with or without an internal dimmer. I have designed several small churches with precisely this scenario. The only conventional dimmers in these churches are the ones that control the house lighting.

So how do you decide if you need a centralized or distributed system? If you are considering a centralized system, you must first ascertain if you have enough room and ventilation for a large dimmer rack. Installing racks can be very expensive, and depending on their location, running power and proper ventilation can be cost prohibitive. You must also figure in the cost of a complete electrical circuit distribution system so that the lights can be powered throughout your church. Also, with conventional SCR dimmers, these high-capacity power circuits may cause cross-interference with nearby audio and wireless communication equipment.

The benefits of distributed dimming includes the flexibility of locating the dimmers where your lights are (easily moving the dimmers if you need to move the lights), using less power, and requiring only a mains supply (usually 20A or 50A single phase per unit) and a control signal (DMX or Wi-Fi Ethernet). There is also significant installation cost savings. The disadvantage is that many of these dimmer modules are of smaller capacity, limiting you to one fixture per dimmer.

Although this may seem to be an easy choice, every church is different with varying needs and challenges. A good lighting consultant can guide you in making the right decisions regarding dimming technology and distribution systems. They can also protect you from those nasty buzzes, and the resulting nasty looks from the sound technician.

David Martin Jacques is a professional lighting designer and consultant. He has designed the lighting for venues in the United States, Europe, and Canada. He serves as Head of Design for California State University Long Beach and can be reached at djacques@csulb.edu .