Lighting in Design Q2 2018

Any person struggling to find a suitable driver not need despair: reputable driver suppliers can be contacted to assist in making the right selection. Programmable drivers Let’s go into a bit more detail about the operating current offered by constant current LED drivers. Many of these drivers offer a single operating cur- rent (350 mA or 700 mA) but we see more and more programmable drivers being used. Program- mable drivers offer not a single operating current but an operating current range (for example, from 200 mA to 700 mA). This greatly increases the versatility of the driver, as the same driver can be used for different LED solutions. Another advantage of programmable drivers is that it is possible to optimise the LED solution for energy-efficiency or lowest initial investment, since a low operating cur- rent increases the efficacy of the solution and a high operating current reduces the component costs. To set the correct operating current for LED drivers, different programming methods are avail- able: using dipswitches, resistors or software and programming the driver using Near Field Com- munication. Programmable drivers are also called ‘window drivers’ as they not only offer an output voltage range, but also an operating current range. When visualis- ing both the output voltage range and the operating current range in a graph it looks like a ‘window’. Im- portant is to realise that the driver is able to offer any combination of output voltage and operating current as long as it is within the window.

- Size/form factor: LED drivers are available in many sizes and form factors, in linear, rectan- gular and round shapes. - Mounting options: Most drivers are designed to be built into a luminaire, but there are also drivers with a so-called strain relief, which can be placed on top of a ceiling and then connected to an LED solution. - Application: As outdoor lighting is a particularly demanding application, there are drivers spe- cifically developed for use in outdoor lighting. These drivers are often potted, have a high immunity against voltage peaks/transients and higher lifetime specifications. Indoor drivers have specifications aligned with indoor use. There are also specific drivers for industrial lighting, these have some of the higher speci- fications in common with outdoor drivers, like higher immunity, and better lifetime in relation to ambient temperature. - Dimming: Many drivers are for fixed-output use. However, there is also a wide choice when it comes to dimmable drivers. Important is the communication between driver and control devices. Communication can be based on protocols like 1-10 V, DALI or DSI, or it can be based on using concepts like phase-cutting or switch dimming (using a bell press). Advice is to spend the necessary time matching the control device/control system with the right driver. - Ingress Protection (IP) rating: Most drivers are rated IP20 and are designed to be built into a luminaire. There are however more and more drivers with a higher IP rating, mainly for out- door applications. - Power factor: Most drivers have a high power factor (usually 0.95 and higher). However, some low wattage drivers might have a low power factor. - Ripple current: The output ripple current of an LED driver determines the ‘ficker’ (better de- scribed as ‘unacceptable light variation that is directly perceived by an average observer’) of an LED solution.The lower the ripple current of the driver the lower the risk of ficker. In this in- stance, knowing the application is important, for example, a driver used in a foodlight installed in a stadiumwhereTV images are recorded should have an extremely low ripple current, while a driver used in a foodlight to light up your yard can have a higher ripple current.

Figure 2: Example of an ‘operating window’.

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LiD Q2 - 2018