Lighting controls in building automation

The selection of LED power supplies with DALI interfaces has always been greater than the selection of KNX LED units. As a result, KNX power supplies were often integrated via a KNX-Dali gateway into modern KNX systems for use in building automation. Now, however, there is a wide range of constant current and constant voltage power supplies available that allow direct integration of LED power supplies into the KNX bus. A major advantage here comes not only from the larger number of selectable functions in the products, but in particular from the dimming behaviour.

There is a difference between measured light intensity and what the human eye perceives. To achieve the best possible visual dimming behaviour and to provide users with different options, KNX LED power supplies such as MEAN WELL’s PWM series offer a choice of three different dimming curves in the ETS application database: The linear dimming curve, the DALI dimming curve, and the logarithmic dimming curve (log).

• The DALI dimming curve is based on a formula specified in the DALI standard and offers users an outstanding dimming experience. The light difference between the dimming levels is designed to remain constant, and the minimum dimming level, according to the DALI standard, is 0.1%. This dimming level amounts to approximately 3% of the light perceived by the human eye.
• The logarithmic curve specifies the logarithmic behaviour. The minimum dimming level using the log curve is just 0.01%, or 1% of the perceived light. The option to choose such a low dimming level takes into account potential use in applications requiring very low illumination levels.

Users are free to choose any one of the three available curves, depending on which one delivers the best result for a particular application.

Changing the light level of constant voltage LED lamps is achieved using pulse width modulation (PWM). Dimming with PWM is suitable for applications that place particularly high emphasis on dimming behaviour. For PWM dimming, however, high frequency is required to avoid flicker and stroboscopic effects and to keep the effect on LED colour temperature to a minimum.

► Tipp: With the power supply units (60, 120 and 200W) in MEAN WELL's PWM series, all offering a KNX interface, users can change the output frequency from 200Hz to 4000Hz via software. The power supplies cut frequencies below 80Hz, the threshold below which flicker can be seen by the human eye. With a maximum PWM frequency of 4000Hz, the units thus meet the recommendations of IEEE 1789-2015 as well as the specifications and limits of the "SVM" (Stroboscopic Visibility Measure) measurement method included in the new ERP Ecodesign Directive for LED power supplies. Regulation (EU) 2019/2020 will enter into force on September 1, 2021.

Constant voltage power supplies are used in four different LED applications:

• With LED strips
• To replace the conventional power supply of 12VAC lamps in traditional design with LED technology
• For direct DC power supply, e.g. for 24VDC LED spotlights
• For operating constant current luminaires using a downstream DC/DC converter.

At Schukat electronic we offer the extensive range of products from manufacturer MEAN WELL. The company has over 35 years’ experience in the development and production of power supplies and LED drivers for a range of applications in lighting and building automation:

• High-quality KNX constant-voltage power supplies PWM-60KN, PWM-120KN, PWM-200KN
• LED constant current series with integrated KNX interface: LCM-25KN, LCM-40KN, LCM-60KN
• Other KNX power supplies and universal switch actuators
• LED power supplies, inrush current limiters, and DIN rail power supplies in overvoltage category III

In addition, our technical sales team is here to help with customer-specific questions about power supplies and more.