Adding value with dimmable LED lighting

John Doyle, Managing Director of Doyle & Tratt Products Ltd, British manufacturer of the Varilight brand of dimmer switches, explains why wholesalers perform an instrumental role in ensuring compatible dimming options are selected by electricians.

Systems MArena Switched

More often than not, dimmer switches are required for a lighting scheme to deliver good aesthetics and flexibility for the user. With halogen light sources, dimming remains a relatively simple add-on but when LED light sources are specified, which is now most often the case, careful consideration needs to be given to dimming control to avoid any performance issues and additional costs.

Unaware of the challenges presented at a technical level, end users will expect their dimmable LED lighting to replicate the performance of incandescent lighting. However, certain characteristics of LED lighting can produce unexpected results when paired with dimmer switches not designed specifically for LED lighting.

For example, unlike incandescent lighting, LED lighting may be sensitive to normal fluctuations in the supply voltage and jump unexpectedly to different light levels. It is important therefore to recommend a dimmer which has a voltage stabilisation feature to prevent voltage fluctuations from affecting the LED lighting it controls.

LED driver

Many LED light sources are not dimmable and this remains the case even if an LED dimmer is used. Whether an LED light source is dimmable or not is determined by the electronics in the LED driver. This might be an external driver, similar in appearance to a transformer, or internal driver, components inside the lamp or fitting itself. Without provision within these electronics, it will not be possible to dim the lights effectively with any dimmer.

If an LED light source has a dimmable driver then, for the best dimming performance, it should be sold with a dimmer that is specifically designed for LED lighting. Specialist LED dimmers are usually packed full of features designed to deliver the optimum performance from dimmable LED lighting. Customers may expect to be able to use a standard dimmer with LED lights that are described as dimmable but attention needs to be drawn to the fact that choosing a specialist LED dimmer are manifold.

Minimum load rating

It might be necessary to address the many technical advantages of a well-designed LED dimmer at the point of sale but a simple reason why a standard dimmer is not suitable is its minimum load rating.

On traditional dimmer switches the recommended minimum load is likely to be 40W, 60W or even higher. Under-loading this type of dimmer is likely to cause flicker, flashing or shimmering effects, which in turn are likely to shorten the life of the LED lamp significantly.

For a successful installation, using an LED dimmer is not the whole story because performance varies between brands and types of lamp and indeed between brands of dimmer. If an end user requests to dim their lights, it is relatively straightforward for you to assist their contractor in choosing a lamp or fitting which is described on the packaging as dimmable.

But how can you easily acquire the depth of knowledge to differentiate between brands of LED and between particular lamps sold under the same brand?

As a leading dimmer switch manufacturer we are only too aware of the scale of that task. Our advice is simple, rather than opening a test laboratory in the storeroom, be sure to recommend an LED dimmer switch from a manufacturer whose product is versatile enough to deliver optimum performance from the various dimmable LED technologies in the market.

Multiple-mode dimmers offer more than one type of dimming technology, typically leading edge and trailing-edge. Both methods are “phase cut” with leading-edge being the conventional way to dim most traditional light sources. Trailing-edge dimming is more difficult to achieve but has many advantages, such as silent dimming and smoother control.

Trailing-edge dimmers

The majority of LED light sources perform better with trailing-edge dimmers. However, to further complicate the issues, this isn’t the whole story as some are specifically designed to be used with leading-edge dimmers. It is even possible that some lamps will prefer trailing-edge dimming up to a certain wattage but leading-edge when there are multiple lamps on a circuit. Therefore, a dimmer with multiple modes, which can switch from trailing to leading-edge dimming, can significantly improve compatibility with a wide variety of LED light sources.

Varilight V-Pro dimmer switches, for example, have three separate dimming modes and an adjustable minimum brightness setting. This approach achieves wide compatibility and delivers the best performance possible from a given LED load. In its default, “out-of-the box” mode, the V- Pro dimmer is compatible with the vast majority of dimmable LED lights on the market.

For some dimmable LED loads the performance can be improved by switching the dimmer to one of the other two modes. It is also possible to make further improvements to the performance of some LED lamps by adjusting the minimum brightness setting of the dimmer.


Due in the main to slight differences in the values of electronic components, an unavoidable part of the manufacturing process and known as “tolerance”, some LED lamps illuminate at a slightly lower power levels than others. If the dimmer being used does not have an adjustable minimum brightness feature then some of the lights may not illuminate at the lowest setting. The unsatisfactory result is that when the lights are dimmed right down some will turn off.

By the same token, if the dimmer is turned on at its lowest setting, some might not come on. By adjusting the minimum brightness setting of the dimmer to a level that is sufficient to illuminate all the lamps in a circuit this behaviour can be eliminated. This feature can also be used to ensure the full brightness range of a particular LED load can be exploited if the minimum brightness level of the dimmer is decreased to the lowest level that the lamps can handle and remain stable.

Further, unlike dimmers for incandescent lighting or halogen, the ratings for LED dimmers often include reference to the number of lamps permitted in the circuit as well as minimum and maximum rating in watts.

In addition to choosing dimmable lamps, an important consideration when helping customers choose LED lamps for dimming is colour temperature. The colour temperature of incandescent lighting decreases when the lights are dimmed, creating a yellower “warm white” light reminiscent of the candlelight that we all associate with a cosy ambience.

To replicate the warm white light of incandescent lamps choose dimmable LED lamps with colour temperatures of between 2700K and 3000K. Some LED lamps have been designed so that the colour temperature shifts to a warmer hue as they are dimmed.

LED strip

There are many more LED light source options available than replacements for incandescent and halogen light bulbs and this is where LED lighting schemes really come to life. LED strip, for example, is an extremely versatile option for under-cabinet, floor level or accent lighting and requires a DC power supply. This can still be controlled as Dimmable AC/DC converters are available from brands such as Varilight to allow customers to dim LED strip with an LED dimmer.

An opportunity clearly exists to trade up to dimmable LED lighting. And, electricians will be more inclined to recommend dimmable options to their clients if guidance to assist the choice is given. In turn, the end user experience can be enhanced by choosing dimmable lamps if the dimmer supplied is equipped with the features needed to produce consistent results.

It is important therefore for wholesalers to be armed with the knowledge to offer their customers the right product using these identifiable pointers ensuring they choose the right lamps and dimmers for a truly compatible dimming solution.