This article was published in the March 2012 issue of LEDs Magazine.
View the Table of Contents and download the PDF file of the complete March 2012 issue, or view the E-zine version in your browser.
I wrote a feature article in the last issue of LEDs Magazine on lighting controls, and lamented the lack of a full standard network stack for lighting systems. Networks and controls will be very important in the continued growth of LED-based solid-state lighting (SSL). It turns out, however, that I was wrong about ZigBee lacking support for lighting. The ZigBee Alliance has recently published building- and home-automation standards that include provisions for lighting control. There are still a few missing pieces relative to SSL, but there is no reason that lighting manufactures should hesitate in adding ZigBee support to their products.
The alliance completed version 1.0 of the ZigBee Building Automation standard back in September. Moreover, the standard has been endorsed by the BACnet organization – the group working under ASHRAE (American Society of Heating Refrigerating and Air-Conditioning Engineers) that defined the BACnet data-communication protocol for building automation over wired networks.
My difficulty in assessing the state of ZigBee is the complex structure of the many different standards and specifications. For example, I had reviewed the building-automation standard and knew there were basic capabilities for lighting such as switching a ZigBee-enabled light on or off, or setting a dimming level. But I found no concepts for grouping fixtures in zones.
I asked Ryan Maley, director of ZigBee Certified at the alliance, about the concept of zones and groups. He immediately replied, “It is in the network layer standard.” The building- automation standard relies on functions embedded in other ZigBee standards. And I knew other documents defined the lower network layers, but I expected the logical concept of zones in the application-level automation standard.
It was Daintree Networks that called my statements about ZigBee into question, and I discussed some specific lighting features with them as well. For example, I couldn’t find any mention of the ability to monitor temperature in fixtures in the lighting portion of the automation standards. Such measurements may be a key to product longevity given the sensitivity of LEDs to hot environments.
Jason Choong, Daintree chief solution architect and vice president of product management, pointed out that there is a command cluster defined in the ZigBee Cluster Library Specification that defines how to implement temperature readings across all product types. Likewise you won’t find the cluster used to measure device power in the building-automation standard.
There are elements of the automation spec that are more focused on legacy lighting than SSL. For example, there is a specific definition of how to measure time since a lamp was changed. There is not an explicit definition of how to deal with an integrated luminaire without a replaceable lamp where you might want to know how many hours the luminaire has been powered on, or how much time has elapsed since a driver was replaced. The definition of dimming in the standard is also focused more on legacy lighting that doesn’t dim linearly, but you can work around that issue.
Choong and Maley pointed out that you can use manufacturer-defined commands for special features. Moreover, the standard will be regularly updated as deployments uncover deficiencies in the document relative to SSL or any issue.
I was also mistaken about the intent of another ZigBee standard under development called ZigBee Light Link. That standard is focused on SSL, but it’s not intended for installations with robust home- or building-automation systems. Instead it’s targeted at simple plug-and-play connections between say a remote control and an LED lamp or luminaire.
My second look at the status of ZigBee has me convinced that the technology is ready for prime time. Daintreee says that in fact its ControlScope product family is fully ZigBee compliant.
Still as things stand now, there are missing pieces. Today you still have to use a dedicated ZigBee controller mated with an LED luminaire to realize a workable system. What is missing is luminaires that have native ZigBee support integrated into the product. Actually, the lighting makers are likely to support ZigBee with some type of modular controller that buyers can specify as an option, and that costs extra. But even that type of add-on is missing for now.
I will be looking closely at Zigbee technology at Lightfair. I want to see if there evidence of support. I don’t see an imminently available alternative, so I would hope that the industry moves to adopt ZigBee and in doing so helps proliferate SSL. Meanwhile we hope to present a comprehensive contributed article on applying ZigBee to lighting soon.