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July 11, 2023
DC lighting refers to the use of direct current (DC) electrical power to illuminate DC lighting fixtures (like LED lighting). A good example of a DC distribution system for lighting is PoE (Power over Ethernet), which converts alternating current (AC) power, into DC power, and distributes it to DC lighting.
What this article covers:
DC lights such as LED fixtures should have DC supplied to them via a DC power source. Unfortunately, alternating current (AC) power is usually what they get (because power grids distribute AC power). This means that LED fixtures, and other DC lighting, need to convert the AC power they get, into the DC power they need. The rectifiers executing these AC to DC conversions can be quite inefficient, often wasting up to 20% of the energy consumed by a light fixture each time it’s turned on. This energy is wasted in the form of heat, which especially impacts DC fixtures if their drivers are integrated (as opposed to remote). When an LED light fixture's driver is integrated, the LED and its rectifier (located inside the driver) are very close together. So, when energy is wasted in the form of heat by an inefficient rectifier, the heat emitted is therefore very close to the actual device, making LED fixtures with integrated drivers more prone to problems caused by thermal runaway.
Thermal runaway is a phenomenon that occurs when heat emitted by inefficiencies in an integrated driver start to wear down a device, creating more inefficiencies, in a positive feedback loop. This ultimately accelerates the deterioration of an LED fixture with an integrated driver (and rectifier).
The result is:
The problem with powering lighting with AC, isn’t with AC electricity itself, but more so with when it’s used in DC lighting applications.
AC power had its moment at the dawn of widespread electrical use in the early 20th century. At the time, incandescent lighting was practically the only option, even though only approximately 2% of the emitted energy from an incandescent source is used as visible light, while the remaining 98% of energy is wasted in the form of heat. Similarly to most electrical devices at the time, incandescent lighting worked on AC power. Thus, it was fitting that AC was distributed to homes and buildings. Now, however, DC consumption makes up about 74% of total electrical loads in homes that use electric vehicles and HVAC equipment with DC motors. In fact, every device that uses a battery or has a screen requires DC power. Consider your laptop, phone, tablet, camera, and everything else that could be considered digital. Despite most of our everyday devices requiring DC power, electrical distribution systems have remained mostly the same as about 100 years ago, and still distribute AC power.
There were, of course, more technical reasons why AC was chosen over DC in the war of the currents. You can read about those reasons on our blog: Why AC Power Really Won the War of the Currents
LEDs are our most efficient lighting option today, usually converting about 95% of their consumed energy into visible light (wasting only about 5% of consumed energy in the form of heat). As mentioned earlier, LED lighting can be made even more efficient by supplying it with the DC power it needs so that no inefficient AC to DC conversions are necessary, which also minimizes thermal runaway in order to get the most lifetime out of LED lights. Additionally, distributing DC power to DC lighting has many more benefits.
Here's a full summary of the benefits of distributing DC power to DC lighting:
1) Eliminate inefficient AC to DC conversions: As mentioned previously, when LED fixtures receive AC power, they need to convert that AC power into DC. Converting AC to DC power is executed by a rectifier that exists within a light fixture's driver. If this driver is integrated, the inefficiencies, emitted in the form of heat, heat up the fixture's electronics. This heat wears down the electronics, and makes them more inefficient, which means that more heat is emitted, and the electronics wear down at an accelerated rate. This positive feedback cycle is called thermal runaway. Distributing DC power directly to LED lighting (or DC lighting in general) eliminates the need for these inefficient rectifiers and, in turn, usually reduces energy consumption in DC lighting by about 20%. It also allows LED lighting to last up to the full lifetime of their LED chips, which is typically around 100,000 hours.
2) Improved reliability of DC devices due to minimal driver deterioration from thermal runaway: To jump off the previous point, LEDs with DC power distributed directly to them last longer. Two specific benefits to this are that LED fixtures won't need to be replaced as often, and they will not flicker.
3) The most energy efficient devices usually require DC power to operate: Distributing DC power can support the proliferation of energy efficient technologies because they usually need it to operate. Here are some examples of energy efficient options for three different markets. Each of these require DC power:
4) Smart systems and devices usually require DC power to operate: The world is shifting towards smarter phones, fridges, door locks, TVs, cars, and more, and there are huge opportunities for energy savings when smart devices and systems are used. For example, you can automate lighting brightness to adjust depending on the availability of natural light (daylight harvesting), which can save up to 70% on lighting if motorized window shades are also automated. The smart bulbs and fixtures used in these systems are usually LED due to their flexibility and energy efficiency advantages over fluorescent lighting. Thus, the lighting in smart systems usually requires DC power. Additionally, smart devices are digital, and therefore utilize semiconductors, which also need DC power to operate.
We need a revolution in just basic electricity before a lot of our smart building technologies will be implemented - Brad Koerner, SBC 2020
Smart systems also offer benefits aside from energy efficiency, take a look at our blog to see what else you can achieve with built-in intelligence: 3 Main Benefits of Smart Lighting
4) It’s less dangerous to come into contact with DC power: Due to the nature of AC power (namely that it alternates at a frequency that makes it able to pass through our bodies, at relatively low voltages), it can more easily interact with our nervous system by penetrating our skin (which is an insulator with resistance, capacitance, and inductance properties). DC power, on the other hand, is still dangerous at certain voltages, but can't penetrate our skin as easily because it doesn't have a frequency, and therefore is blocked by the capacitance of our bodies. Thus, AC is less safe than DC at the same voltage.
5) DC lighting could act as a tailwind for the proliferation of renewable energy sources like solar: The more devices that use DC power, the more demand there will be for DC power generation. While traditional sources, like hydroelectric, nuclear, and coal power plants generate AC power, more renewable sources like solar generate DC power. When AC power is generated, but needs to be converted into DC power, large rectifier equipment is necessary, which can lead to extraordinary costs in transmission. One way to cut down the cost of this equipment is to generate DC power directly with solar. At the moment, there are technological challenges that prevent solar from being generated at a large scale. Storage and voltage regulation technology, for example, haven't reached the point where high voltages of DC power can be generated, stored, and stepped down when necessary. To explain this further, AC power is compatible with transformers, and DC power is not. Transformers are devices that can easily step voltages up or down depending on voltage requirements, and they also isolate electrical power for safety. In order to use DC power in transmission systems, rectifiers must therefore be used to convert DC power into AC before it’s stepped up or down (with a transformer). Then it can be converted back into DC. Thus, depending on if AC has to be converted back into DC after the fact, 1 - 2 large scale rectifiers are necessary in HVDC transmission. The cost of this additional equipment can often be justified because of how efficiently DC flows through cables, but only at a “break-even” distance (about 600 km). For now, DC power can much more realistically be generated and distributed at a smaller scale. It’s commonplace to see solar panels on the roofs of buildings, such as schools and offices. These DC microgrids supply energy sustainably, and can also provide DC devices, like LED lighting, with the DC power they need. If more people decide to distribute DC power to their DC lighting, this could be one of the driving factors pushing for the proliferation of renewable energy sources like solar, even if it's only used to generate power at a small scale for now.
Despite the challenges involved in large scale DC power generation and transmission, there have recently been big strides in small scale DC power distribution, see our blog to learn more about fault-managed DC distribution systems. These are an alternative to DC microgrids that still provide DC power to devices that need it: The Next Big Thing In Energy Efficiency: Fault-Managed Power
So now you know why DC lighting should be powered with DC electricity, but how exactly does this work? There are a few different methods of small-scale (building level) DC power distribution, so it's easiest to explain DC power distribution to DC lighting through the use of an example. Two prominent small-scale DC power distribution systems are Class 2 and Class 4 rated power systems. Class 2 and Class 4 are ratings given by the National Electrical Code (NEC) in the USA to DC power systems that meet specific criteria. Class 2 power systems are generally low-voltage (up to 100W), and are considered safe from both fire and electric shock hazards. Power over Ethernet, and Cence LVDC are considered Class 2 rated power systems. Class 4 rated power systems are a new addition to the NEC as of early 2023, and can be found in Article 726 of the 2023 version of the NEC. This addition was made to acknowledge, and standardize, the emergence of fault-managed, DC power systems. Fault-managed, Class 4 rated power systems can monitor cables for a defined set of faults using a Class 4 transmitter and receiver at either end of a cable. These systems shut power off almost immediately if a fault is detected, which allows Class 4 systems to be considered safe from fire and electric shock hazards in the same way that Class 2 systems are. The main difference, is that Class 4 power systems can distribute much higher voltages than Class 2 systems, with a capacity to distribute up to 450V DC along cables and no real wattage limitation.
Depending on the system, Class 2 systems can accept a handful of different power input types. Cence LVDC, for example, can connect to 4 different types of power inputs: renewable energy microgrids, energy storage, AC electrical panels, and Class 4 DC power. The main power supply in a Class 2 power system, such as on the one in the lower compartment of the Cence LVDC panel, can be either a rectifier or a Class 4 receiver. For example, if Class 4 power is sent to this main power supply, the system steps down voltage levels, and distributes Class 2 power (100W) through internal drivers, which regulate voltages depending on the needs of the connected light fixtures. If AC power is sent to the panel, however, then the internal rectifier makes one, centralized conversion from AC to DC power, and regulates the voltage level to distribute Class 2 power in the same way through the drivers on the panel. Essentially, main power supplies in Class 2 systems can operate as voltage regulators, so that the appropriate type of power, and voltage level, are sent to LED drivers, and then sent to connected light fixtures.
Class 4 power systems are usually connected directly to a building's AC electrical panel. Class 4 transmitters receive this AC power, regulate it, and transmit up to 450V DC of Class 4 power to Class 4 receivers or transceivers (a combination of a transmitter and receiver) along fault-managed cables. Class 4 transmitters contain rectifiers to convert power from AC to DC, and they adjust voltage levels in order to send Class 4 power to Class 4 receivers (or transceivers). Essentially, Class 4, fault-managed, power travels from transmitters, along fault-managed cables, to receivers or transceivers, which act as the final voltage regulator before power is sent to connected light fixtures. These transmitters, along with the receivers, or transceivers, additionally have integrated safety computers that intelligently monitor cables for faults, and shut power off if any occur. In this way, cables can be monitored for faults from point A to point B, along the entire length of cable (which can be up to 2 - 3 km long). Providers of fault-managed, Class 4 power systems include Voltserver, Panduit, and Cence Power. Being fault-managed is what allows Class 4 power systems to send such high voltages, while often still making use of low-voltage wiring practices.
To delve a little more deeply into when a Class 4 transceiver vs. receiver would be connected to the initial transmitter, it comes down to daisy chaining. If you'd like to maximize the power yield of a Class 4 transmitter, and make use of its total available power at 450V DC, then it's ideal to connect more than one light fixture to each transmitter. In order to do this, receivers must be both transmitters and receivers so they can transmit Class 4 power, as well as receive it.
There you have it, that is an example of how a Class 2 or Class 4 DC power distribution system works at a small scale (when applied in a commercial, industrial, or multi-residential building, for example). However, there are other features that define a DC distribution system for DC lighting. For one thing, an electrical system can either be centralized or decentralized, or have remote (external) or internal drivers. Additionally, some systems, like the Cence system, have an added layer of intelligence by providing a secure mesh network for all system components, and connected devices, to wirelessly connect with.
A centralized DC lighting system sends DC power from one, central location, to connected devices, whereas a decentralized system powers each light fixture at an individual level with decentralized drivers. Class 2 power systems are typically centralized, as shown in the diagram above, so they regulate voltages and distribute power directly to LED fixtures from centralized locations.
Class 4 power system, on the other hand, can be considered both centralized and decentralized. This is because, although they regulate and transmit power from centralized transmitters, the individual, external transceivers also regulate voltages, and send the appropriate power to connected light fixtures.
The primary consideration in a DC power distribution system for DC lighting, however, is really just that it eliminates individual AC to DC conversions that can be prone to thermal runaway, and cause premature failure of connected fixtures. Both Class 2 and Class 4 power systems achieve this by executing a centralized AC to DC conversion at the panel level. The only voltage regulation necessary after this point is DC voltage regulation in the case of the Class 4 system.
A major problem with traditional AC systems for DC lighting is that these AC to DC conversions are decentralized, meaning they are executed at an individual level by drivers connected directly to light fixtures. As mentioned earlier, these conversions are typically inefficient, and cause light fixtures to fail prematurely.
You can read more about the benefits of centralized power systems on our blog: Make Buildings More Efficient With Centralized Power Systems
DC lighting systems can be further defined by differentiating between remote (external) and internal drivers. In traditional AC power systems for DC lighting, the drivers are typically built into the light fixtures and are therefore considered "internal". This is because they are not separate from light fixtures. This is typically the case, so that AC power can be connected directly to the fixture. Remote drivers on the other hand, are separate from light fixtures. Remote drivers have many benefits, one being they are not limited by space constraints, and can therefore be larger than internal drivers. Because they can be bigger, they can also be more efficient (and usually are) without being more expensive.
Aside from remote drivers typically being more efficient, they are also easier to maintain because they can be located in easier to access locations. Additionally, they can regulate voltages for multiple LEDs as long as those LEDs can be daisy chained together, this is opposed to internal drivers, which can only be connected to individual LED fixtures. Because of these three benefits (efficiency, ease of maintenance, and multi-fixture support), it's ideal for LED drivers to be remote. In the diagram above, you can see an example of a Class 2 and 4 power system with remote drivers.
You can read more about remote vs. internal drivers in our blog all about them: The Most Efficient Remote Power Systems
Maybe you’re wondering what the difference is between AC and DC power anyway. The root difference between the two is the direction the electricity flows; DC power travels in a straight, direct path on a graph of voltage vs. time, whereas AC power alternates polarity 50 - 60 times per second. This gives AC power a frequency, and having a frequency results in both negative and positive outcomes. For one thing, having a frequency means that AC power is compatible with transformers, which often makes it inexpensive to step up voltages for long distance transmission. In fact, this is ultimately why AC power was chosen as a result of the war of the currents. On the other hand, having a frequency makes it more prone to line losses than DC power. Because DC power has no frequency, it’s not prone to any line losses except for some types of resistive line losses. This is what makes it cheaper to use a high-voltage DC transmission system after the break-even distance of 600km (as discussed earlier).
If you’re interested, you can read more about line losses in our blog about them: The 3 Types of Line Losses
In conclusion, supplying DC lighting with the DC power it needs is an approach that’s quickly gaining traction for it's efficiency, and more. AC lighting, such as incandescent bulbs, are significantly less efficient than DC lighting such as LEDs, and supplying AC power to DC lighting makes DC lighting less energy efficient. Eliminating AC to DC conversions in DC lighting with DC microgrids, or another form of DC power distribution, results in increased energy efficiency, and minimizes thermal runaway. This not only translates into cost savings but also contributes to a more sustainable future by minimizing energy wasted in lighting. The rise of smart lighting, which also relies on DC power, further underscores the advantages of DC lighting, enabling advanced control, automation, and energy management features. Additionally, DC lighting can serve as a tailwind for renewable energy generation, particularly solar power. Since solar panels produce DC electricity, utilizing it with DC lighting systems simplifies the overall energy infrastructure and promotes the utilization of clean and renewable energy sources. As we move towards a greener and smarter future, DC lighting holds immense potential for transforming the way we illuminate our spaces.
We improve the value of commercial and multifamily buildings with an intelligent DC power distribution system that's pain-free to install. It combines the benefits of low-voltage wiring practices with voltage capabilities of up to 450 Volts DC.
