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DALI and daylight harvesting

Taking your over-the-counter lighting offer up a notch with DALI and daylight harvesting

Peter Staniforth, Technical Manager, Timeguard Ltd

If you thought DALI  and daylight harvesting was mainly for the big contractors dealing direct with manufacturers think again.  They are finding their way into the mainstream wholesaler channel, with one of the most trusted brands in the channel throwing its hat in the ring with a new range of DALI-compatible PIRs. The Timeguard reputation for quality and great support at the end of a phone line, will be encouraging more installers to add to their offer. After all, and as you sales figures will show, they are happy with relatively complex zoned heating and lighting systems – why not DALO and daylight harvesting?

What is it?

The Digital Addressable Lighting Interface (DALI) is a standard that enables different devices on a system to talk to each other – they don’t even need to come from the same manufacturer. It’s an international standard, specifically created for lighting, for a two-way communication system that gives easy control and versatility. In a traditional system, control signals are one-way. In a DALI system, signal traffic is two-way, meaning LEDs can be commanded to perform requested actions, such as switch ON/OFF or DIM, but they can also be asked to provide information. The LED driver or switch can provide, for instance, information about intensity and energy consumption, or it can simply verify that it is working. 

A DALI network consists of a controller, a power supply (which may be built into the controller) and one or more slave devices (eg ballasts, drivers, dimmers and PIR detectors) that have DALI interfaces. The controller can address devices individually or by multicast. Each device can be assigned to up to/any of 16 groups and can store up to 16 scenes that can be controlled by a single command

DALI sends messages around, and just like computer networks, the ballast with the right address picks the message up and follows the instruction: it might be ‘turn all the lights in the corridor on’, or it could be ‘switch to the theatre lighting scene in the conference room’.  

Now that you know the basics, the decision may be a little more straightforward. Do you want to light several multi-function rooms that require different lighting options depending on time of day, usage etc. If so, think about DALI control with the new Timeguard range.

When to use DALI?

There are clearly cases and places where ordinary lighting is fine: if the application is simple and doesn’t require daylight harvesting (an important energy saving feature now specified in Building Regulations) , dimming, occupancy control or individual user control,  DALI isn’t the answer. But when installers do need to design in or add any of these functions, then it is well worth a look . 

A DALI system just needs a DALI bus for communication between different points on the system such as the controller and a PIR.  So, an extra pair of cables between devices and control points of the system is needed : standard 2-core, minimum 1.5mm2 is sufficient. A DALI loop can contain up to 64 devices – typically LED drivers or PIRs - with multiple loops linked for larger projects.

When to opt for daylight harvesting

If the project doesn’t warrant DALI scene setting, then installers can use these new PIRs as standalone detectors and offer their customers daylight harvesting. That’s just another way of saying that lights will turn on and off in response to changes in the natural light, as the sun goes  in and out, as well according to the time of day. You may also have heard this referred to as constant light control and, in the past, it has been the preserve of PIR detectors designed – and priced – for the top end of the market.

This article first appeared in Wholesaler & Electrical Distributor, June 2018.

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