Markets: Lighting Control


as being dimmable, and we’ve gone along and they’re just not. We have to say to the client, ‘I’m really sorry, but this dimmer is just an on-off switch.’” So said Simon Buddle, technical director of residential integration company SMC, at a roundtable event last year organised by AWE Europe and which I chaired for our IE Residential newsletter. The situation he describes is clearly an unsatisfactory state of affairs. But which types of lighting are most susceptible to dimming problems like this – and what can be done about them? It turns out – somewhat ironically –


Dim and dimmer W


e’ve ended up on projects where someone else has specified the light fittings


that it’s the lower-energy alternatives to traditional incandescent lighting that, to a greater or lesser extent, have proved difficult to dim. Erik Larsen, market manager at ETC,


provides a historical perspective: “As soon as you move away from high- voltage conventional incandescent lamp technology, the troubles start. The first challenge here came with the move in commercial and residential lighting towards using low-voltage halogen lamps to increase efficiency. Dimming low-voltage electronic transformers was a challenge for traditional leading-edge dimming technology, and we saw trailing-edge dimmers developed to better handle that problem.” [See box item opposite.] So far, so good. But then we turn to


compact fluorescent lamps (CFLs), which, like their linear counterparts, contain a dimming ballast – in the case of CFLs, this is built into the base of the lamp. CFLs can be designed to be dimmable, but those that are built cheaply – such as the lamps that utility companies sent out free of charge to households in the UK and elsewhere in


Dimming can be a challenge for some lighting technologies


Europe – are not. For these lamps, an external dimming ballast could also be specified but, again, this would require extra spending. Even CFLs that have been designed


to be dimmable have not been free of difficulities. “There have been attempts to release mains-dimmable CFLs but these have not really ever performed to the standard of halogen or incandescent dimming,” says Mark Tallent, lighting and building controls product manager for Crestron UK. One issue here is that the cathodes


within fluorescents need to be kept hot in order to function, so the minimum current that this requires generally means that they cannot be dimmed below 20%.


Shedding some light However, the most contentious technology when it comes to control and dimming must be LED lighting – the subject of Simon Buddle’s comment at the start of this article. Guy Simmonds, energy solutions


‘LEDs in particular


don’t dim very well’ Austen Conway, Helvar


36 IE April 2012


manager at Lutron, points out that whereas dimming incandescent lighting requires just a controller and the fixture, with LED there is a driver unit in between – so there are two links in the chain (from controller to driver and from driver to fixture) that can potentially throw up issues. In addition, the driver manufacturer is generally not the same as the lamp manufacturer, increasing the


possibility of incompatibilities. Simmonds adds that when it comes


to overall energy efficiency of LED lighting designs, the efficiency of the driver is key. “LED companies often talk about the efficiency of the lamp, but the efficiency of the driver usually isn’t quoted,” he counsels. “LEDs in particular don’t dim very


well,” says Austen Conway, R&D director at Helvar. “You can see a massive variation in dimming performance between two different manufacturers’ drivers… Also, I’ve seen some retrofit LED lamps that dim over a wide range, while others only dim over 30% of the range available.” “All the other technologies are


several decades old,” points out Simmonds. “LED suffers from being the new kid on the block, and from the fact that it is evolving so quickly.” At the roundtable event, Philippe


Regnier of Philips Dynalite described the absence of standards for LED control as “a massive mess”, and explained that this situation has arisen because the technology lends itself to small-scale manufacturing: “[With LED] you can start your business in lighting by making luminaires in your garage. Previously the entry level was so high that it was quite easy to frame that industry. Now it’s a mess, and that’s why it’s so complex for [integrators] to use LEDs within their projects.” Conway explains some of the


Key points


. Once you move away from incandescent lighting, most modern lighting types present difficulties if you are looking for complete dimmability from 100% down to 0%


. Because of a lack of standardisation, particularly with LED, the only sure-fire way to know whether a combination of dimmer and fixture will dim as desired is to test it


. Even when dimming performance is as desired, the resulting change in colour temperature may not be


difficulties: “All LED drivers have a minimum level below which their LED produces no light output. The problem is these levels are all different, so using a dimmer with programmable minimum levels for each channel is a must. On slow fades having too low a minimum level for the driver results in a long delay before anything happens, then each lamp coming on at a different time.” Another issue sometimes encountered is for a driver to produce a sudden reduction in light level as the control is set to full. “To solve this problem, set the maximum level of the dimmer to, say, 90%,” he advises.


www.installationeurope.com


The move to more efficient forms of lighting has not been entirely smooth; in particular, some types of lighting do not exhibit anything like the same dimming performance as their incandescent equivalents. Paddy Baker sheds some light on the subject


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