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Use DALI, LED converters for high-tech dimming

Posted: 16 Aug 2013 ?? ?Print Version ?Bookmark and Share

Keywords:Digital Addressable Lighting Interface? DALI? light management? LED? luminaires?

The Digital Addressable Lighting Interface (DALI) international lighting standard is now firmly established in the professional lighting industry. It stands for intelligent light management that enables different lighting levels to be easily controlled, different lighting scenes to be set up and flexible adjustments to be made to lighting systems to allow for different room usages.

The benefits of DALI light management systems which have been designed specifically for professional lighting solutions in the commercial and architectural sectors are evident. These systems are easy to install and scalable. If used correctly they offer considerable energy savings of up to 80 per cent. Installation is made easy thanks to uncomplicated wiring. They can also be integrated in building management systems with very little effort. And no specialist knowledge is needed to operate these systems.

Lighting to suit the situation perfectly
With DALI it is possible to design the lighting to cover very different requirements and to change the lighting without the need for any further installation work C also for LED luminaires. This means that energy-saving daylight-controlled scenes can be set up as well as application-related lighting scenes, for example for office workstations or meeting rooms. On a DALI line up to 64 digital dimmable ballasts can be individually addressed and assigned to 16 different groups, and 16 lighting scenes can be programmed for each group. If the room usage changes, the luminaires can be easily assigned to different groups in a software package. There is therefore no need to any rewiring or modifications to the luminaires. It is basically possible for all the individual luminaires or the luminaires assigned to a group to be separately addressed, switched on and off, controlled and dimmed via the relevant control gear.

DALI control gear for LEDs
Control gear with DALI interfaces are now available for all light sources on the market, including LED. These LED converters are as easy to link to DALI systems as control gear for conventional light sources. The full scope of the DALI standard has been implemented in the ECO series of dimmable converters, so these can be easily programmed via the DALI interface. In view of the method in which they fade up and down, however, LED converters must be specifically matched to the characteristics of LEDs. This is because at low current amplitudes LEDs often tend to display shifts in the colour location or exhibit unwanted brightness tolerances, with the result that they do not always meet the visual requirements of the users when dimmed.

The new series of converters has been tailored to these special LED characteristics. The converters offer excellent dimming behaviour and have a dimming range of 1 to 100 per cent. They use two different dimming methods, namely analogue dimming between 100 and 35 per cent, and pulse width modulation from 35 down to 1 per cent. This ensures optimum operation throughout the entire dimming range because pulse width modulation means there are no shifts in the colour location at low current levels, and analogue dimming provides the necessary high resolution at the top end of the dimming range. The converters ensure that the connected LED light sources can be used for stripe-free photography and filming even at dimming levels as low as 35 per cent, and even if simple cameras are used which record images line by line. The energy efficiency of the lighting system can be improved not only by dimming but also by a reduction in standby losses. At less than 200 mW they are extremely low for this new converter series.

Some devices on the market suffer from a 100Hz current ripple which then has an effect on the LED module. In such cases, luminaire manufacturers have to build in a reserve for this ripple component when defining the nominal current, at the expense of efficiency. ECO converters allow the efficiency of the LED module to be fully exploited because the module can be operated up to the limit of the specified current.

Protection for the luminaire and the converter
Integrated protective functions such as ITM (Intelligent Monitor Guard) and ITG (Intelligent Temperature Guard) together with temperature sensors make sure that neither the LED module (and therefore the luminaire) nor the converter is exposed to high temperatures. Several temperature thresholds are provided to ensure that the prescribed temperatures are not exceeded C by temporarily dimming the lamp or, if absolutely necessary, by switching the lamp off. In this way the light source will have a long life and the high-value DALI luminaire will be protected. If the system of LED module and converter is integrated in a building management system and a light source is dimmed as it reaches a critical temperature or is switched off via the DALI interface a fault reporting can be generated.

Thanks to its reliability and dimming performance, the new converter series is capable of supporting various expansion options and is ideally prepared for the future with its fully implemented DALI interface. This is also evidenced by its CE/ENEC and RCM certification and its imminent CQC certification. With the aid of appropriate software it is also possible to implement further lighting functions via the DALI interface, such as reduced output at night for street lightingan application in which LEDs are now being used more and more.

About the author
Juergen Fink is Head of Global Product Management Gears at Tridonic.

To download the PDF version of this article, click here.

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