Solid-state lighting is energy efficient, but it has been questioned whether there is a more efficient way to power it. Thong Hunyh and Alec Makdessian explain how Power over Ethernet (PoE), technology provides networking and control benefits to LED lighting systems that AC mains cannot.
Solid-state lighting is energy efficient, but it has been questioned whether there is a more efficient way to power it. Thong Hunyh and Alec Makdessian explain how Power over Ethernet (PoE), technology provides networking and control benefits to LED lighting systems that AC mains cannot.
Solid-state lighting (LED-based) is becoming a mainstream technology. It replaces incandescent, compact fluorescent, and halogen lights (CFLs), in residential, commercial, and industrial settings. The many benefits of LEDs can be seen in their longer operating life, greater energy efficiency and small size for small-form factor fixtures. An LED lamp’s 50,000 hour lifespan is much longer than that of incandescent lamps (1000 to 2000 hours), and CFLs (5000 to 10,000 hours). Because LEDs last longer, they are easier to replace and lower labor costs. LEDs are also cheaper to operate, and the brightness of a 10W LED bulb is approximately the same as a 60W incandescent lamp.
Although LED lights have many benefits, it is still unclear how to best power them. We will explain how modern power over Ethernet (PoE), can provide DC power to LEDs. System efficiency is comparable to that of traditional AC mains power. The PoE technology is more efficient when you consider the advanced benefits of using Ethernet local area networks (LAN) to network the lights and the lower maintenance costs.
DC power combined with PoE technology
Inherently, LEDs can be used as low-voltage DC devices. Most LED drivers for lighting use an AC to DC converter to convert AC mains power into a lower DC voltage. This ensures compatibility with AC power. Designers have suggested DC-based power systems to reduce system efficiency. A few studies have shown that a DC-powered system is less expensive than the AC system. Carnegie Mellon University2 found that DC can be used to save $2,000 annually over AC. You could save even more money by using DC instead.
You can supply DC power to LED lamps using PoE technology today. This regulation is set by IEEE 802.3, which was originally published in 2003. It was updated in 2009. This standard requires that power and data be transmitted over a single standard network cable (e.g. Cat5) directly to connected devices. The power-sourcing equipment (PSE), located in the switch/hub, provides power. A powered device (PD) is the connected device that receives power, such as the LED lamp in this example.
The PSE supplies more power than the PD’s limit to account for worst-case network cable power loss. According to the original PoE standard (IEEE802.3af), the PSE should supply power at a maximum 15.4W for a voltage range between 44 VDC and 57 VDC when using Cat3 or higher cabling. The PD is restricted to 13W for a voltage range of 37 VDC to 57VDC. The IEEE802.3at standard later extended the power capabilities to 30W (PSE), over a 50VDC to 57VDC voltage range using Cat5 and better cabling. This scenario limits the PD to a maximum draw limit of 25.5W for a range of 50 VDC to 57VDC voltages. IEEE 802.3bt, which is expected to be ratified shortly, will increase PoE power capabilities. The minimum power level at PSE output can reach 90W.
RJ45 Connector
Each LED light fixture can be powered by PoE and can be a standard RJ45 connector plug-and play device with an individual addressable IP address. The LED fixture can be made smarter by adding sensors. This configuration allows each intelligent LED hub to collect data on temperature, humidity, ambient lighting, and other room-occupancy data, which it then transmits back to the controller. In this example, occupancy sensing could ensure that the lighting is turned on when someone enters a space and off when they are not (Fig. 1). Ambient light sensors are also able to enable daylight harvesting5 and adjust LED lighting to keep constant lighting even when there is no sunlight. PoE is ideal for connecting and controlling smart LED hubs via a LAN.
The LED lighting system is now part of an IT network. It can reach other services and buildings beyond the immediate area of the user, as well as any device connected to the network (e.g. phone, tablet, or PC). The system’s proximity sensors can be used by users to locate the nearest meeting room. Facility managers and owners now have a complete view of their facility’s energy consumption. Management can monitor, control, and measure all nodes in the network, including heat and ventilation, in real-time, allowing them to identify potential energy savings and operational efficiency improvements. This information allows them to adjust the temperature, lighting, or cleaning schedules based upon historical user behavior.
LED lighting fixtures
Futureproofing is possible with a PoE network of LED lights. The smart sensor hubs and LED lighting fixtures are already placed where they are needed, with power and data wired to the most important locations. Fig. 2 shows how new communication or sensor modules such as short-range wireless access point distributed short-range wireless access can be easily added to existing systems at a low cost and with minimal labor. 2).
This is where it leads us. PoE makes it clear that IP-enabled devices can be deployed and installed at a lower cost. This applies to sensors as well as LED lamps. Because data and power are shared on the same cable, cabling costs are lower. Installing the network cable requires no licensing. This means that installation costs are lower. The PoE DC voltage is safer than 110 VAC (or 220VAC) and makes installation easier. PoE networks allow for better network power management. They provide both control over the power of connected devices and backup power in case of power outages. Super Bowl(c), which saw 35 minutes of darkness, was an example of PoE technology’s added value.6 The stadium’s Wi Fi(c) network, powered by PoE with battery backup, was unaffected.
These are just a few of the many benefits that a PoE-connected lighting system offers. They have also rekindled the AC versus DC power debate. Many people wonder about the ohmic loss that Cat5 (or better), will cause. Some might wonder if these losses are low enough to allow for efficiency improvements.
We examine three possible scenarios to power a 10W or 20W LED lamp. These PoE scenarios will follow the IEEE802.3af (15.4W PE and 13.0W PM) and the IEEE802.3at (30W, 25.5W) standards. AC is based upon the standard mains power of 230 VAC.
What effect does length of cable have on efficiency
Fig. 3 is a block diagram showing a typical PoE lighting system. The mains power of 230 VAC is fed to a CUI Inc PSE-1000 1000W power supply. This has a 90% efficiency. The 40W MAX5984 PSE controller controls the PSE, while the 70W MAX5982 controller controls PD. The Cat6 23AWG cable has 67O/1 km of 0.067O/m per Strand. Fig. Table 3 and Table 1 give more information about the assumptions.
Futureproofing is possible with a PoE network of LED lights. The smart sensor hubs and LED lighting fixtures are already placed where they are needed, with power and data wired to the most important locations. Fig. 2 shows how new communication or sensor modules such as short-range wireless access point distributed short-range wireless access can be easily added to existing systems at a low cost and with minimal labor.
AC versus POE: The ultimate comparison
If you assume a dimmable LED fixture, your AC system efficiency (82.9%) will only be slightly higher than that of the 10W PoE fixture with the maximum length 100m cable (82.3% efficiency). The AC efficiency of the 25m Cat5 cable is actually lower at 1% (82.9% vs. the PoE LED lamp’s 83.9%). The PoE system efficiency decreases as the power of individual fixtures rises and it becomes less efficient than AC.
The lighting requirements of each application will ultimately determine the efficiency of an AC system versus a PoE system. If the output power of each PoE system is low and the length of the Cat5/Cat6 cable is shorter, then PoE power efficiency will be superior to an AC system. The more precise the lighting, the more efficient the PoE-powered LED will be compared to AC power.
Although LED lights have many benefits, it is still unclear how to best power them. We will explain how modern power over Ethernet (PoE), can provide DC power to LEDs. System efficiency is comparable to that of traditional AC mains power. The PoE technology is more efficient when you consider the advanced benefits of using Ethernet local area networks (LAN) to network the lights and the lower maintenance costs.
One more note. Our analysis assumed that 23AWG Cat6 cable resistance was used. PoE lighting efficiency can be improved even more by using 22AWG Cat6 cable resistance. This is not as common, but it could become more widespread as PoE lighting becomes more popular.
Conclusion
The system efficiency was the only focus of our previous analysis. The actual costs of system installation were not taken into account. Local rules and regulations will determine the cost of permits and licensing electricians to install lamp or system. These labor costs are necessary to compare the cost differences between AC and PoE-powered lighting.
We must remember that LED light fixtures powered with PoE can be easily paired with wireless communication modules and embedded processors to create smart hubs. The LAN can be connected to smart LED lighting/sensors hubs. This will enable the hubs to support emerging technologies such as the Internet of Things (IoT), without the need for additional lighting replacement.
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