Provisions in the new IEEE standard for power over Ethernet make it easier to use PoE in lighting applications.
While power over Ethernet (PoE)-based LED lighting has been available for the past half-dozen years, there hasn't been much attention devoted to this technology in the LED lighting industry until relatively recently. With the recent release of IEEE 802.3bt-2018 – IEEE Approved Draft Standard for Ethernet - Amendment 2: Power over Ethernet over 4 Pairs, that may be about to change.
PoE was initially used in proprietary Voice over Internet Protocol (VoIP) systems developed by Cisco in 2000 and each new generation of PoE standards and technology included higher power specifications. At the same time, LED luminaire efficacies have improved year over year so that by 2017, the 25.5W limit of the now superseded IEEE 802.3at standard sufficed to power nearly a quarter of all indoor luminaires.
The IEEE 802.3bt standard, approved by the IEEE Standards Association Board on September 27, 2018, includes some significant enhancements for LED lighting systems. The main driver of this improvement is the specification for up to 90W of delivered power for cable lengths of up to 100m through the use of all four pairs of wires. This allows for daisy chaining of several luminaires, which can simplify the installation process.
A power over Ethernet network. Source: H. E. Williams, Inc.
Other enhancements in the new spec include improved efficiency for current PoE levels of 25.5W of delivered power as the power loss in the cable is reduced by approximately half. For example, power sourcing equipment operating under the previous standard needed to supply a minimum of 30W to ensure that the power device receives 25.5W because as much as 4.5W can be lost in the Ethernet cable. Powering the same device under the new standard will reduce losses to less than 2.25W, translating to about a 7% efficiency increase.
In addition, the power sourcing equipment will now have the capability to determine the maximum power drawn by each connected device and set the delivered power accordingly, resulting in improved overall system operation. Last, the standby power requirements are now lower due to the reduction of the required duty cycle of the maintain power signature signal, with a mere 0.02W required to maintain a powered connection. As energy efficiency is probably the most compelling selling point for LED lighting systems, the changes in the new spec can help make the case for PoE control systems.
A recent visit to H. E. Williams, Inc. in Carthage, Missouri proved to be very illuminating (no pun intended) in terms of the nuts and bolts of PoE systems. As shown in the block diagram above, a PoE lighting system includes five basic components: the network controller, the user interface(s), the PoE switch, the luminaires, and any auxiliary devices such as sensors or switches.
Data and power delivery to the luminaires is accomplished via the addition of a "node" mounted inside the luminaire housing and connected to the LED light engine power and dimming inputs. Depending upon the capabilities of the connected luminaire and its associated auxiliary devices, other functionality is handled by the node as well. Igor Inc’s node allows multiple devices to be connected to a PoE network.
PoE network node from Igor Inc. Source: H. E. Williams, Inc.
The yellow PoE port in the image above provides the Ethernet connection to the PoE switch. The blue port functions via constrained application protocol and is used for daisy-chaining to other luminaires or auxiliary devices such as sensors. The network node in its enclosure measures 3.875×3.5".
With the new IEEE 802.3bt standard, Igor has made some modifications to the node form factor so that it more closely resembles traditional LED driver dimensions. Another nifty enhancement is the incorporation of a USB port as shown in the lower left-hand corner of the image below.
Igor's IEEE802.3bt-compatible PoE node. Source: H. E. Williams, Inc.
Due to the reduction in the number of AC-DC power conversions, PoE lighting systems can offer improved overall energy efficiency in comparison to traditional AC line voltage systems. Ethernet cable loss appears to be the main concern in terms of assessing total system power consumption, a metric that is particularly important to end-users seeking utility rebates for energy efficiency improvements.
NEMA/ANSI C137.3-2017 Minimum Requirements for Installation of Energy Efficient Power over Ethernet (PoE) Lighting Systems provides installation requirements. Specifically, the standard establishes the minimum wire gauges to limit average resistive line losses to less than 5% of the total power delivered assuming a 50m average cable length. However, since each installation is more or less unique, the total loss must be assessed on a case-by-case basis. Currently no standards exist for guidance on assessment methodology.
—Yoelit Hiebert has worked in the field of LED lighting for the past 10 years and has experience in both the manufacturing and end-user sides of the industry.