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Markets: Lighting Control Trailing and leading edges


Old-fashioned rheostat dimmers worked by adding a variable resistance into the lighting circuit. They were inefficient because they simply diverted electrical energy away from the lamp and dissipated it as heat. Instead, modern dimmers work by switching on the current to the circuit at an adjustable time during each half-cycle of the AC supply. There are two kinds of dimming in common use. Trailing-


edge dimmers are on at the zero point of each half-cycle and switch off partway through.


Leading-


edge dimmers switch on part- way through the cycle and stay on until the zero- crossing point.


The high peak currents from leading-edge dimming can create buzzing in LED drivers. Trailing-edge dimming is usually silent. If a driver specified for trailing-edge dimming is used with a leading-edge dimmer, the high peak currents may damage the driver or reduce its lifetime. Universal dimmers can operate in both


modes and are suitable for mixed load types or when the nature of the load is not known.


Progress is being made when it comes to dimmable, colour- shifting energy efficient products


While it’s clearly a problem if a dimmer doesn’t dim at all, how much does it matter if the dimming range is a little restricted? “Not all types of lighting applications need a dimming range from 100% down to 0%,” points out Larsen. “In many commercial applications it’s enough to be able to adjust from 100% down to closer to 20%, working with daylight sensors to simply adjust the light level based on daylight conditions.” The consensus is this: don’t assume


that any type of low-energy lighting will dim in the way you want to. Test out samples of the products prior to


installation, or find some documented proof that the dimmability you require is achievable. For larger projects, you may find the control manufacturer will do this on your behalf. Simmonds points out that Lutron’s website features results from the company’s LED testing centre. “We take lamps from the major manufacturers, and test how they perform against our various dimmers,” he explains. Once the question “Will it dim?” has been dealt with successfully, the next question is “What will it look like?” Tallent says: “The key reason for dimming has always been to create ambience. Traditionally, dimming a light source always resulted in less output and more warmth. Although recent years have seen vast amounts of R&D and investment in LED technology, the biggest challenge to the lighting manufacturers is still the accurate replication of halogen or incandescent when dimming energy- efficient light sources.” Larsen echoes this point: “In talking


about the challenge of dimming, we have not even touched another serious issue that has come very close with the demands for power saving technology:


light quality. Discharge lamps, and especially LED technology, do not have the same spectral quality as we used to have with tungsten – but that is another story.” Obviously, some sectors have been


more accepting of these shortcomings than others: most commercial lighting sectors have tolerated them, but, says Tallent: “Residential and hotel sectors have suffered most due to the lack of warmth, colour consistency/rendition, temperatures and different outputs within each room.”


Facing the challenge Progress is being made year on year, though he adds: “Currently, the challenge is for lighting manufacturers to launch the first dimmable, colour- shifting energy efficient product – but many are still on the fence as to whether replicating incandescent or halogen will be truly achievable.” So, what will the future bring?


Conway points to two initiatives that are likely to make for easier lives all round in the near future. The first is the Enlight project – a Europe-wide initiative, currently in the first year of its three-year duration, with the stated aim of exploiting the full potential of solid-state lighting. Co-ordinated by Philips Lighting, the project’s 30 partners include global lighting manufacturers, semiconductor companies, knowledge institutions, a utility company and innovative small and medium-sized enterprises. With the aim of delivering energy reductions of 40% compared with LED retrofits, Enlight is pursuing breakthrough innovations on the use and integration of LED modules, non-conventional lighting, and intelligent lighting systems. “They will go a long way towards standardising solid-state dimming, which is the thing that we lack currently,” says Conway. While Enlight is aimed mainly at commercial and corporate lighting, a second initiative has more resonance in the residential field. IEC


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‘As soon as you move away from high-voltage conventional incandescent lamp technology, the


troubles start’ Erik Larsen, ETC


standardisation work is taking place on digital loadline transmissions (DLT) which would drive the trend towards localised rather than centralised dimming. He explains: “Dimming would be done locally at the lamp, so you could retrofit a DLT lamp, put in a DLT dimmer, and then dimming could be targeted at that lamp.” A more distant prospect, Conway


reports, is retrofit lamps that contain a dimming engine and IP addressability built into the base of the lamp. This conjures up an image of absolute control of dimming from any device with a web browser. However, it also raises a variant of the classic question: how many IT support staff does it take to change a light bulb? IE


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IE April 2012 37


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