Guest post by Steve Mesh
Power over Ethernet (PoE) lighting is part of a brave new world. The ascendance of LED fixtures has given rise to some new methods of providing and controlling light in our environments. Since LEDs are low-voltage devices that use direct current, they are a good match with a system that provides low-voltage DC power over Ethernet cables. Guess what? That’s a computer network! For several years, lighting (and computer) companies have been developing the idea of powering LED fixtures from what is essentially a computer network switch. As you might imagine, this gives rise to a host of questions about a variety of issues.
Centralized vs. distributed network switches — Typically computer network “switches” reside in IT closets in the core of the building. In that case, every single light fixture would require its own home run of Ethernet cable back to the IT closet. Light fixtures typically require more power than many of the other devices in a computer network. Therefore, there has been substantial voltage drop associated with first-generation PoE lighting systems where every fixture has its own home run. Obviously, this is also a lot of Ethernet cable runs back to the IT room. Some companies have developed “distributed” switches that are designed to be mounted in the plenum. This helps to reduce the voltage loss associated with a system that only uses one centralized network switch to send power to the lights.
Even though IT staff tend to prefer when everything is terminated in the IT closet, so they know where it is, lighting is a different animal. Perhaps these distributed switches in the plenum will become the norm for PoE lighting installations. Additionally, these systems typically have an initial “burn-in” function so that the settings selected in the software are written to the PoE devices – in this case, light fixtures. For example, some PoE fixtures have microprocessors as well as flash memory. That allows each fixture to store values that you set in the control system’s software, such as occupancy sensor time delays, target ambient light levels, schedules, etc. If the network goes down, then the fixtures can still operate as programmed until the network has been reestablished.
Installation — Some of the initial proponents of using PoE to power LED fixtures were from outside the lighting industry. Even so, lighting designers and engineers wanted to know who would actually install a PoE system – IBEW electricians who typically install line-voltage equipment or CWA electricians/technicians who typically install low-voltage equipment (data/signal, etc.). Depending on location, CWA electricians/technicians may charge less than electricians who install line-voltage equipment. That was part of the initial draw of PoE systems. However, historically, architectural light fixtures have been always installed by electricians qualified to install line-voltage products. So what happens when PoE fixtures and network switches are delivered to the job site? Someone has to install them – but who? This may be a good time for a paradigm shift in how architectural light fixtures are powered. However, even if that time has come, there will still be a transition period where people will have to work out these kinds of issues.
Right now, the most common scenario is for the electrician to mechanically install the fixture and plug in the Ethernet cable to the fixture. Then everything upstream from that (back to the switch in the plenum or in the IT closet) is done by a system integrator or datacom contractor.
Emergency lighting — PoE lighting systems use Ethernet cables which carry low-voltage to the fixtures. Therefore, there is no line-voltage at these fixtures. Typical methods of emergency lighting using the normal architectural fixtures use line-voltage power. Historically, there have been two major methods: 1.) using fixtures with integral batteries and transfer circuitry, so only power from a normal panel is needed, and 2.) bringing power to designated fixtures from emergency (EM) lighting panels. Some newer lighting control systems use a hybrid — i.e., where the EM fixtures are supplied from an EM power panel, but power from a normal panel is used by special EM relays to sense normal power loss. In that case, the relay(s) have to bypass the lighting system controller’s relay and also 0-10V (or any other) dimming signal.
Since PoE light fixtures wouldn’t normally have or use any line-voltage power, manufacturers making PoE lighting systems have had to rethink the methods for providing EM lighting. One method is to use a UPS (uninterruptible power supply) connected to the network switch. This is essentially the same thing that anyone would use to make sure that essential computer won’t shut off during a power loss. UPS’s have batteries that provide electricity immediately upon a power loss. Keep in mind that there are specific NEC and/or other regulations that govern how much light is required along the path of egress during a power failure, and for what duration of time (usually 90 minutes). Therefore, a UPS used for the purpose of providing EM power to PoE light fixtures must have the capacity to do so.
In any given locale, the authority having jurisdiction (AHJ) may or may not accept the use of a UPS in conjunction with a PoE lighting system. It really makes sense to determine this before making any final purchase decision about a PoE system. If the AHJ does not (or will not) accept the use of a UPS system, the only other solution may be to use wall-mounted “bug-eye” fixtures. Many owners will not accept this. According to Gary Trott of CREE Lighting, there are manufacturers that are starting to develop integral batteries for use with PoE light fixtures. This is a typical method of providing emergency lighting in applications such as office spaces, etc. When these manufacturers get integral battery units certified for use in PoE fixtures, that may be a great new solution to this problem.
Product offerings — Since PoE systems require drivers suitable for PoE power supply, you can’t just buy any fixture and use it in a PoE installation. Remember that LED drivers used in PoE fixtures are powered from Ethernet cables coming from a network switch. That means that these drivers are designed for low-voltage DC supply (as opposed to line-voltage AC supply like normal fixtures use). So far, manufacturers offering PoE light fixtures have fairly limited offerings. For example, a vendor might offer a typical recessed troffer and a round downlight. This may be adequate for a large percentage of interior spaces, but there will be applications requiring different kinds of fixtures – i.e., wallwashers, accent lights, pendant-mounted direct-indirect fixtures, etc. Unless and until vendors expand their PoE light fixture offerings, some spaces might require a mixture of PoE fixtures with other fixtures supplied by line-voltage AC power.
Peripherals — PoE light fixtures typically have integral sensors (occupancy sensors and photosensors). The signals from these sensors travel along the Ethernet cable back to the hub/server. Ethernet cables contain 4 pairs of thin-gauge wires (i.e., 26-gauge). If a PoE system uses 3 of these pairs to send power to the light fixture, the 4th pair can still be used to send data back and forth to the control system.
Keep in mind that almost every interior space requires some form of local control. Essentially this means a wall switch/dimmer. Manufacturers make wall switches/dimmers that tie into the PoE system using the same Ethernet cable. For retrofit situations, it might be valuable if vendors made peripherals (such as switches and sensors) that use a wireless signal to connect with a centrally located wireless gateway. As a result, you could avoid having to run wires down existing walls. Unless and until such peripherals are offered, PoE systems are easy to install in new construction projects where the Ethernet cables can easily be run throughout the plenum as well as down the walls to switch locations.
IoT — This is a big buzzword. What does it actually mean? According to Cree’s Gary Trott, IoT means “different software and different hardware work together to provide value that hasn’t been offered before.” That’s a broad definition and as such, in practice, this can encompass lots of different types of programs and products. What kind of added value can a PoE lighting system offer? Gary tells the story about a building in North Carolina where to date they have collected millions of lines of data. If every fixture has its own occupancy sensor (which PoE fixtures typically do), then the owner’s staff can develop a very precise history and knowledge about occupancy rates, patterns, schedules, etc. They can also get information about when conference rooms are in use (as compared to when they are scheduled, which may not be the same). If there are discrepancies, the owner can ask employees to be more responsible about reserving common spaces.
Power-over-Ethernet lighting and control systems are certainly the new kids on the block. It will take time for specifiers, electricians and code inspectors to get used to this radical new method of providing light in interior spaces. Make sure to ask lots of questions about anything that will affect the lighting and controls in a given application. This is very new stuff, and remember that it’s not the manufacturer’s responsibility to make sure that your installation will comply with all applicable code and life safety requirements.