The Internet of Things: PoE Lighting
Written by Dave Harris, trueCABLE Technical Specialist, BICSI INST1 Certified
The Internet isn’t just for people anymore. Nowadays there are actually more devices operating autonomously on the Internet than there are people. So what kinds of “things” are on the Internet? Among other things, they include telephones, cameras, security devices, wireless access points, smart doorbells, refrigerators that report on their contents, and even a connected toilet seat that tracks the user’s blood pressure. It is predicted that many more devices will feature Internet connectivity as more technologies are developed.
One of the most useful technologies in the Internet of Things is connected lighting. The light fixtures themselves are connected to the Internet, so that they can respond to signals from other devices on the Internet. Switches, dimmers, occupancy detectors, light meters, and smart window shades can now all share data to provide more convenience for the occupant as well as more efficient use of energy.
However, more and more electric devices means more and more AC electrical pathways and more ballasts and transformers for fluorescent or LED light fixtures, all of which create electromagnetic interference (EMI). In a commercial installation, most of the electrical conduit and light fixtures are located above a suspended ceiling. Some of those spaces are starting to get kind of crowded. In some cases, it’s hard to find any room to install copper Ethernet cable where it will be safe from EMI (See “Top 2 Things to Consider When Running Ethernet and Power Cable.”)
Figure 1. Above-ceiling space in a commercial installation. With all the AC electrical conduit, it’s hard to see where one might install Ethernet cable. And with all that EMI around, you would definitely want to use shielded cable! (Image by Singleton Electric Company)
Figure 2. Above-ceiling space in a seventy-year old hospital building. So much technology has been added over the decades that there is no space left for anything new. Those green cables are for a new Wi-Fi system rushed for the benefit of COVID patients. Yes, they are definitely shielded.
Most new lighting installed in commercial buildings these days uses an LED source. These “Light Emitting Diodes” run cooler and use less power than any other current lighting technology. (See Table 1.) They are also able to change color and intensity in response to data input. Another important attribute of LED lights is that they are powered by low voltage DC current. So every LED light fixture that uses an AC power connection must not only depend on relatively high-voltage AC power cables, but it must also use a transformer to step the voltage down and rectify it to DC power which actually runs the lights. AC power lines, transformers and rectifiers are all sources of EMI, which can cripple network performance. If only there were a local source of DC power for the LEDs, a whole lot of cable, conduit, transformers, and EMI could be eliminated.
Hmm, ever hear of PoE?
Table 1. Power in watts consumed by different types of light sources at various light outputs. Note that LED lighting is the most efficient light source.
Power over Ethernet (PoE)
Power over Ethernet (PoE) is a technology that allows low-voltage DC current to be transmitted over the same cables used for data transmission. This enables devices like cameras, wireless access points, telephones, and even some Ethernet switches to operate without a separate source of power. In most cases, the Ethernet cable does not need to be installed by a licensed electrician, which saves on installation costs.
Another important advantage of PoE is that AC current continuously emits EMI. DC current does not.
Recent advancements in PoE technology now make it possible for Ethernet cables to transmit up to 100 watts of DC power while maintaining data transmission performance. Now PoE can power things like HVAC servos, smart window shades and yes, even lighting.
For more information about PoE, check out “The Power of PoE.”
With light fixtures that are powered by PoE, only one Ethernet cable needs to be run to the fixture. That cable transmits both DC power and data. If routed using cable trays or J-hooks, much less conduit needs to be installed, which saves on installation costs.
Figure 3. A light fixture that runs on PoE. The only cable connected to the light fixture is an orange Ethernet cable. The bundles behind the fixture are the horizontal cables for data (blue) and PoE lighting (orange) for this wing of the building. There are large HVAC ducts, water pipes, and fire suppression pipes, but the only AC conduit runs are mounted high and against the wall. And with no transformers needed for the lighting, very little EMI can be expected to proliferate in this area.
Using PoE-powered LED lighting offers many advantages over traditional lighting technologies. They include:
- Lower construction costs
- Lower cost to operate and maintain
- No separate emergency lighting system is required
- Lights can change color to respond to situations like fire drills, storm warnings, God-forbid an active shooter, etc.
- With no AC transformer required, lights run cooler, use less energy, and require less physical space
- Connected lighting can interface with sensors, PoE window shades, and environment controls to save money and reduce carbon footprints
There are a couple of possible issues to be aware of when designing a PoE lighting system. The first issue is heat generated by DC power running through the relatively narrow conductors used in Ethernet cable. This is not nearly enough heat to offset the heat produced by traditional lighting, but it should be considered in any design. Transmission of heat can be reduced by the use of shielded cable. Most negative effects of this heat can be mitigated by simply deploying smaller cable bundles. Nevertheless, cable manufacturers are busy designing Ethernet cables that attempt to deal with the radiation of heat by experimenting with larger wire gauge sizes, and cables with discontinuous shields. See Power over Ethernet (PoE) Installation Best Practices for more detail on controlling heat radiation in PoE installations.
Another issue is the sheer number of cables that will need to be run back to the telecommunications room (TR). Figure that your TRs will now have about twice the number of Ethernet cables compared to a traditional lighting installation. Be prepared to design and build larger TRs with a lot more cable. Additional racks, patch panels and PoE switches will probably also be needed. Nevertheless, when compared to the initial cost of a traditional lighting installation, PoE lighting wins the competition by far.
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