The intention was to mimic a typical small installation where there are existing GU10 filament lamps on a dimmer and where the client simply wants to swap them for LED versions.
We obtained popular LED GU10 lamps from five different manufacturers. The lamps were typically 5W – 6W and produced 400lm – 500lm. We then put four identical lamps on a mains track (so the load was 20W – 25W) and connected it to a range of wall-plate type dimmers.
The one indisputable conclusion is that you should use a dimmer designed for use with LEDs. Some 'tungsten' dimmers worked fine with some LED GU10 lamps and not with others. The results varied widely. The dedicated LED dimmers almost always performed better.
Some GU10 will continue to work even though they are flickering quite badly. We have simply noted the point where flicker starts to become really noticeable. Since flickering and instability most often occurs when dimming to low levels, some dimmer manufacturers have an adjustable minimum brightness setting so that the lamp simply switches off at a certain point.
We used some dimmers that were specifically designed for LED loads and also some that were for regular, filament GU10 lamps. The latter represents the situation where there is an existing dimming system and where the client doesn’t want the expense/work of changing it.
Some dimmer equipment manufacturers produce compatibility charts but due to the huge range of GU10 LED lamps on the market it is impossible to cover every product. More lamps come on to the market every month. Besides, the GU10 lamp manufacturers frequently change the internal circuitry of their lamps, even within the same range and having the same product reference. A lamp type that is compatible today may not be compatible a few months later simply due to changes in production. The reverse can also be true.
DIMMER: Budget brand dimmer suitable for GU10
The Enlite, GE, Kosnic and Verbatim all dimmed to below 20 percent. The Enlite and GE performed particularly well. The Supacell would only dim to 35 percent and it was noisier at all levels. The Verbatim did flicker slightly at some intermediate levels but this could be cured by adjusting the output up or down a small fraction.
DIMMER: MK Logic Plus
To be fair, the instructions do say that the dimmer is not suitable for any kind of fluorescent or Energy Saving lamp. However, we chose it because MK is a highly reputable, quality manufacturer and this dimmer will have been in tens of thousands of installations.
It gave smooth dimming down to less than 10 percent on all the lamps bar one. Most produced a slight hum. The Kosnic performed particularly well and was silent. Unfortunately, the Supacell wasn’t really compatible; below about 50 percent, the flicker was too severe.
Of course, MK also make dimmers suitable for LED GU10 but we wanted to test a retrofit situation.
DIMMER: Hamilton H-LEDSTAT
This is an 'intelligent' dimmer suitable for LEDs. At the initial power on, you push the button for a few seconds and it then automatically selects the best dimming mode. You can also select a minimum lighting level. It dimmed all the lamps smoothly and silently down to less than 5 percent. It even held the Verbatim steady at 1 percent. The only exception was the Supacell which would only dim to about 35 percent.
DIMMER: Doyle and Tratt V-Pro
This is another dimmer designed for LEDs. It worked straight out the box and gave smooth operation with all lamps. It even managed to dim the Supacell to about 10 percent and other lamps were as low as 1 percent or 2 percent.
DIMMER: Lutron Rania
Rather than a rotary knob, this has a sleek, brushed stainless steel faceplate with a push On/Off plus Up and Down arrows. There is a column of seven minute pinholes which glow green depending on the dimming level.
At initial switch-on, there is a slight pause as the circuitry chooses the best dimming mode. It was then smooth and silent down to less than 5% with all the lamps except the Supacell.
Most lamps performed fairly well on all the dimmers. The exception was the Supacell which worked best with the V-Pro. We told Supacell of our results and they say that new versions of this lamp will have an improved NXP driver. This should reduce flicker and noise.
The firmest conclusion is that if you have an existing 'tungsten' dimmer, you should change it for a dimmer specifically suited to LEDs.
The Doyle and Tratt, Hamilton and Lutron dimmers were designed for LEDs and produced much better results over the whole range of lamps. They were quieter and dimmed to lower levels.
- Look for a dimmer with an adjustable 'minimum brightness' setting. Many dimmer manufacturers offer this option and it helps to avoid any instability at low level.
- Make sure the LED load is above the minimum for the dimmer. Many dimmers have a minimum load, say, 20W. If you are connecting just a few low wattage LEDs, you need to exceed the minimum load required. If this isn’t possible, adding a resistive load can often help and many dimmer manufacturers offer one as an accessory.
- Don’t overload the dimmer. This is unlikely if you are replacing filament GU10 lamps by their LED equivalent. However, if you are buying a new dimmer specifically for LEDs, you may find that it has one wattage rating for filament GU10 and a lower wattage rating when using LEDs. This may be 25 percent lower or an even smaller wattage.
We would like to thank the companies mentioned together with Danlers and Fab Controls for their assistance with this article.
- You can find out more about dimmers at Lux Live, which will take place on the 23-24th of November 2016 at the Excel Centre in London. It's free to attend and you can find out more here.