May 2008 Issue
Buyer's Guide

Transistorized Dimming

As the entertainment industry’s love affair with automated lighting has cooled a bit over the years, its interest in conventional lighting is as strong as ever. Sales of dimmers are at an all-time high and there’s no indication that they won’t continue to grow. There’s little mystery about it. Conventional luminaires offer warm light, good color rendering and very smooth dimming at a reasonable cost. They’re easy to understand, easy to maintain and easy to program and operate. But the news isn’t all good.


ETC Matrix MK II Dimming System 


With the heightened awareness of sustainable living, the rising cost of depletable resources like oil and coal, the falling cost and increasing output of LEDs and the development of alternative technologies like short-arc discharge lamps, compact fluorescent lamps, T5 and T8 fluorescents, conventional lighting is being closely scrutinized in every application. And there’s good reason for it. Incandescent lamps are among the most inefficient sources around. They convert about 3.5% of the energy they consume into visible light, and at 20 to 30 lumens per watt for an HPL, they lag far behind more efficient lamps like CFLs (about 60 lumens per watt) and MSRs (about 80 to 90 lumens per watt). But in many ways, it’s hard to beat the good old incandescent lamp. It’s familiar, it’s not overly complicated and it’s easily accessible the world over. And that’s why sales of conventional lighting and dimming are as strong as they’ve ever been.

Strand Sine Wave Dimmer Module 

There are more efficient incandescent alternatives on the horizon. Last year, General Electric announced that they are working on a High Efficiency Incandescent (HEI) that will eventually reach about 60 lumens per watt. And David Cunningham, the inventor of the Source Four, is working on an incandescent lamp with an infrared-reflecting coating that will improve the efficiency substantially.

Strand Dual Dimmers

But both of these new incandescent technologies have yet to make an appearance in prototype form as far as we know, leading one to wonder when and if they will ever be a reality. Until then, there are some steps that can be taken to maximize the efficiency of dimming systems. Transistorized dimming, including both forward and reverse phase- control IGBT (insulated gate bipolar transistor) dimmers and sine wave dimmers, offer marginal improvements in efficiency since they don’t use conventional filter chokes. But just like conventional SCR dimmers, even transistorized forward and reverse phase-control IGBT dimmers still produce harmonics, resulting in consumption of wasted “reactive” power that performs no work.  This is typically dealt with by using K-rated feeder transformers, but it’s an inefficient solution. K-rated transformers are designed to handle the extra heat generated by harmonic currents, but they contribute to the inefficiency of the system under low-load or no-load conditions, which, in a dimmer system, is most of the time.

ETC Matrix MkII iSine 4x3kW Dimmer Module

On the other hand, only transistorized sine wave dimming draws current in a sinusoidal waveform, and therefore does not generate harmonic currents. Therefore, K-rated transformers are not required in a dimming system using only sine wave dimmers. But for those of us who don’t have the budget for an all-sine wave dimming system (they have a significant price premium over other technologies), or don’t require absolute quiet in lamp filaments (the primary feature of sine wave dimmers) there is another green option.

Swisson XSD Sine Wave Dimmer 

Harmonic mitigating transformers (HMTs) are designed in such a way that third-order harmonics – the most troublesome of harmonics – do not re-circulate in the primary of the delta-wye transformer feeding the system. Therefore, they avoid generating waste heat and are also much more efficient with low loads or no load.


Swisson XSD - 148 Sine Wave Dimmer Rack

HMTs and transistorized dimmers are relatively new technologies , but they could be the technology of the future. To learn more about transistorized dimming, check out our Buyer’s Guide and talk to the manufacturers about what they have to offer.

Thanks to Steve Terry for providing the information about HMTs.


To view a PDF of the April 2008 PLSN Buyers Guide chart, click here .

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