It has never been a more exciting time to integrate LED lighting into residential spaces.
Lighting and interior designers have access to an ever-widening range of lamps and fixtures, with modern LED lighting systems now offering colour-temperatures akin to the lovely warm tungsten sources of yesteryear, yet with significantly higher efficiency. The days of cold or flickering LED lamps are over, or at least they can be. The long-lifetime expectations of LEDs mean that the light source no longer needs to be a user-replacable item, in the way that a filament lamp was, but instead fixtures can be designed with new shapes made possible by integral LED light-engines, which do not need to be replaced. LED fixtures enable lighting permutations that were not possible with traditional replaceable lamp packages.
This LED era is arriving at just the right time because new EC legislation, which comes into effect in September 2016, will remove directional halogen lamps (such as the ubiquitous GU10 type) from sale, with the same fate following for non-directional lamps in 2018. This energy-efficiency promoting legislation will inevitably fuel further growth in the LED lamps market, as they are used to fill the millions of sockets vacated by blown, “banned”, lamps.
However, all is not necessarily straightforward in the world of LEDs! Simply replacing older halogen light sources with new retrofit LED lamps can lead to problems with flicker, poor low-end-dimming performance, audible noise problems and even interference with other products (such as AV systems).
The part of the overall LED system which has most effect on performance is the “driver”. The “driver”, also known as the Electronic Control Gear, or E.C.G., is the part of the system which converts the incoming mains voltage (the 230V alternating-current, or AC) into the low-voltage direct-current (DC) required by the LED array. Different LED arrays require different voltages and currents.
All LED systems contain such a driver. In retro-fit lamps it’s hidden away with the lamp envelope, often within the stem, just above the cap used to connect to the lamp-socket. For LED fixtures the driver is sometimes inside the fixture housing or often connected “remotely” via trailing cables.
The nearly instantaneous response of the actual LED chips (the part which emits the light) to a changing current makes them highly susceptible to flicker, especially when compared to older incandescent sources where the filament’s white-hot temperature meant that instantaneous darkness from the lamp was not possible, and the slower cooling suppressed most fast flicker issues. One of the most important LED driver features (regardless of type) is the quality and consistency of the DC output voltage of the driver.
There are many types of driver, including Constant Current (used for driving LEDs in a series string with a fixed current to determine the brightness), and Constant Voltage (used for driving LED tape, where the exact length, and therefore the total number of LEDs to be powered, is unknown prior to installation).
There are two methods to dim an LED driver, and the right type must be selected according to the design of the driver:
- Chopping up the mains supply to the driver, also known as phase-cutting or mains-dimming
- Using a driver that accepts a fixed mains supply, and also a low-voltage control signal, such as DALI or DMX. The low-voltage signal is used to instruct the driver how much power to deliver to the load.
When mains-dimming, which is most common for retro-fit LED lamps because the driver only has mains connections via the lamp-cap, the challenge here in Europe is that whilst there are many standards for product safety which apply to lamps and fixtures, there are no industry standards by which to ensure the compatibility of light-sources and dimmers.
This means that the only way a designer can be certain that a system with retro-fit LED lamps will work satisfactorily is to test each combination of lamp and dimmer, as different combinations will yield wildly different performance.
Verifying compatibility must go far beyond a simple “look and see” test of dimming, as invisible issues such as inrush currents, power-factor problems, or electrical and audible noise, may variously affect both flicker, interference and system life.
Such thorough testing is very time-consuming, but in the absence of performance standards it is the only route to achieving success in the real-world conditions of a building project. Lutron freely publishes lamp-testing results at www.lutron.com/LED to assist designers in selecting from a wide range of lamps from different manufacturers. Over two thousand different lamp sku’s have been tested to date.
When controlling LED fixtures, rather than retrofit lamps, greater success can be achieved using a driver which takes a fixed mains supply along with a low-voltage signal. The low-voltage signal gives instruction to the driver circuit to indicate what proportion of the output power should be applied to the load.
Such instruction is communicated via a protocol such as DALI, DMX or a varying analogue voltage.
These techniques are less prone to flicker because the driver’s input power supply remains unchopped, meaning that the driver circuit will always have the power that it needs to perform the voltage conversion, no matter what brightness level is desired. Some protocols, such as DALI, offer greater immunity to electrical interference than others, such as 0-10V control. Other proprietary protocols exist, which give increased stability in larger systems. Flicker issues when using these methods are usually down to a mismatch between the driver and the LED load.
Whatever type of LED is used, compatibility, longevity and proper performance are only properly determined by thorough testing. The good news is that with good quality lamps, and robust controls, the LED era opens up many exciting possibilities to greatly enhance residential lighting projects.
Sam Woodward is Lutron’s Customer Education Leader for Europe & Africa. He also the co-author of the “IET Code of Practice for the Application of LED Lighting Systems”.