Friday, 5 April 2013

Turn your lamps down low...

The incompatibility of legacy dimming systems originally designed for use with incandescent lamps is causing headaches for lighting designers when they use them with LEDs. Nick Martindale reports and collects some best practice tips
Over the past few years LEDs have emerged as a viable means of enabling clients to save energy while giving lighting designers flexibility and the scope for greater creativity. Yet for many designers and customers there is a flaw: the thorny issue of dimming, particularly when attempting to retrofit LED lamps or luminaires into existing mains-dimmable systems.

For Peter Veale, co-director of Firefly Lighting Design, this has become an issue of late. “When a manufacturer comes in to show us their wares my first question is to ask whether they dim,” he says. “They say we can have any dimming we want, and that used to reassure me.
“But, after a particular project last year, where the LEDs weren’t dimming as much as we or the client had hoped, we now have to go a bit further and ask if we can have a sample of the driver we would get if we specified it, so that we can test it,” he adds. “A lot of clients have been in the halogen world and are now using LEDs and expect them to dim in a halogen way. But that’s not necessarily the case.”
James McKenzie, chief executive of LED solutions provider Photonstar, says the whole industry has made heavy weather of the dimming issue by attempting to support legacy systems such as trailing and leading edge that were originally designed for incandescent lighting. One problem is that of minimum load – the point where legacy dimmers cannot cope with the low power required by LEDs – while the quality of the dimmers themselves can also cause problems in an LED world.

Minimum load

“LED drivers are having to get incredibly sophisticated in a bid to guess what dimmer you’re going to use with the system,” he says. “It’s not just the dimmer that’s the problem, either. The wiring can create extra rings that the dimmer manufacturer doesn’t have a clue about. You have to ask why we’re trying to dim LEDs using an incandescent dimmer.”

The issue of minimum load is a particular problem with LED lamps, which often have an integrated driver and electronics combined with the LEDs themselves, says Peter van der Kolk, business development director at controls manufacturer Helvar UK.
“In many cases these LED lamps use phase-cut dimmable technology, which was originally optimised for conventional light sources, such as tungsten and halogen,” he says.

Alan Hayllar, engineering director at Mode Lighting (UK), says the problem has been made worse by the failure of LED manufacturers and distributors to confirm which products will dim, and to what extent. “Many of the LED manufacturers claim dimmability, sometimes with certain caveats, but many products do not fully live up to that claim,” he says. “If they stated they could be dimmed but also specified any limitation, it would enhance the reputation of LED products in the market.”

Fred Bass, managing director of Neonlite International – the brand owner of Megaman – suggests that only the “more serious industry players” are prepared to put in the legwork and provide accurate compatibility lists, but also points to the lack of a standard for phase-cut dimming.

“When making a lamp, because there is no standard for the dimming circuit it is going to run on, the only way to know if it will dim correctly on a circuit is to put it into a luminaire and see if it works,” he says. “In the worst cases, the lamp won’t work at all, but more commonly you may get unstable operation at lower dimming levels.”

As a partial solution, designers are sometimes advised to install resistors or even phantom loads to ensure transformers are able to detect the LEDs.

“We’ve talked to lighting controls people who have suggested putting in a ghost load, like a bulb in the ceiling, but that seems a bit detrimental if we’re trying to be energy-efficient,” says Veale. “I might suggest it as a last resort but I’d hope we could get transformers that could take a very low load.”

Compatibility issues

The issues of minimum load and lack of compatibility are not confined to lamps.

“Despite luminaires and downlighter fittings having more room for the electronic driver, they appear to be just as difficult to dim,” says Julian Kay, managing director of controls firm Danlers. “The only way to determine whether any lamp, dimmer and ballast combination will be successful is to carry out detailed analysis of the electrical waveforms.”
Guy Simmonds, head of sustainable solutions (Europe) at Lutron, warns that compatibility can be a significant factor in the overall performance of an installed scheme.

“One of the complexities is that there are two factors to consider: the compatibility between the LED driver and the control, but also between the driver and the lamp,” he says. “Everything needs to be working together in order to maximise performance for the designer and end-user.”

Controls protocols

The use of controls protocols such as DALI, DMX, DSI and 1-10V goes some way to alleviating these issues, with the dimming carried out by the ballast itself and the dimmer only acting as a controller, particularly in new installations.

“The use of controls protocols allows the employed electronics – drivers and ballasts – to control the lighting in an optimal manner for efficiency, long life and performance, whereas mains phase dimming compromises the ability of the electronics,” says Jason Ford, project manager for lighting management systems at Osram.

Even this is not without problems, however. Darren Orrow, director of lighting design consultancy Into, points out that on 1-10V with a good driver, LED and controller combination it should be possible to achieve minimum dim levels of 2-5 per cent of maximum brightness.

However, some combinations may only allow an LED to dim to 10 per cent of its maximum level, and this will need to be borne in mind at specification stage.

“DMX, DALI and mains dimming where remote drivers are used will allow you to dim lower, to 0-3 per cent of the maximum level, depending on the combination, but there are different costs associated with such dimming systems and compatible drivers,” he says.

But, on mains dimming where the driver is integral to the LED lamp dim, levels below 5 per cent are sometimes not achievable without instability, he adds.

The whole area has become such a headache that his firm has had to employ a full-time technical manager whose job it is to ensure compatibility.

Test samples

For now, the best designers and specifiers can do is to ask manufacturers for accurate information on compatibility or request samples of equipment so they can run their own tests before they make any purchase.

For McKenzie, though, there’s also a role to play in educating clients, possibly steering them away from dimming altogether.

“People mostly dim to save energy and they’re already doing that by installing LEDs,” he says.

In the longer term, he adds, the easy retrofit might be to replace the switch plate with something that could talk wirelessly to the fittings, thereby bringing down the cost of the more expensive protocols by making them less difficult to install.

In the short term, though, lighting specifiers will have to make the best of a bad situation.

“LED dimming compatibility is only likely to get worse on existing installations using phase cut dimmers, as more people transfer their incandescent lamps to LEDs,” says Bass. “In the long term, the only way that people are going to overcome this will be to replace their existing dimmer with a more LED-compatible model if they want the best of both worlds: energy-efficient lighting from LEDs and dimming.”


Because there are so many variables in LED dimming, it is difficult to produce a definitive checklist for lighting specifiers. So Lighting teamed up with the specialists quoted in this feature to highlight five tips which apply across the board:
  •  Manufacturer advice on compatibility is not exhaustive. Request a sample and test it yourself. 
  • Remember that with luminaires or downlighters you will need compatibility between the driver and the lamp, as well as dimmer and the driver. 
  • Consider the use of controls protocols such as 1-10V, DMX or DALI in new builds or large refurbishments. 
  • Be conscious that certain systems will not dim all the way down. If you want complete dimming, use DMX, mains or DALI with the correct drivers. 
  • Ask clients if they really need to dim. If it’s for energy- efficiency reasons, point out they will use far less energy than before, even without dimming. 

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