It's no surprise that LED lighting continues to carve out an increasingly larger share of the $50 billion lighting market, given its superior energy efficiency compared to CFLs (fluorescent lamps) and incandescent bulbs. However, LED luminaires are expensive to manufacture due to the high cost of the LEDs and their heat dissipation design. In addition to competing with CFLs on energy efficiency, LED lighting manufacturers must differentiate their products by offering more advanced features than their CFL competitors.
For example, LED luminaires can easily provide color retention, meaning the same LED can emit warm white or cool white light, or any color in the color spectrum. CFLs cannot currently do this. Communication capabilities also make LED luminaires smarter and enable better control, diagnostics, and automation. Since all lighting fixtures connect to power lines to convert electrical energy into light, many manufacturers want to use power line communication ( PLC ) interfaces as the primary communication and control link.
Power line communication
Power lines form the world's largest copper wire infrastructure. With power outlets in every corner of homes and office buildings, power lines are a completely enveloping network. Communication of everything from basic color and brightness information to more complex information such as color schemes (predefined color patterns for different light fixtures) and fade-in/fade-out (color transitions) can be achieved without installing any new wiring. Furthermore, leveraging advanced fixture discovery and binding mechanisms abstracted from the user, a PLC-enabled lighting control network can be established without remembering a number or risking accidentally turning off a neighbor's lights.
Powerline networks employ a bus topology, offering high configurability and enabling control of multiple devices from a single controller. This controller can manage all lights in a room, or even all lights in a house. Furthermore, the bus topology allows multiple controllers to control a single light. Thus, lights in one room can be controlled by lights in other rooms (e.g., turning off all the lights in the house from the bedroom). This topology also allows the controller to continuously track all devices on the network and act as a backbone server, enabling scalability and "plug-and-play" installation; any new light can immediately become part of the network.
Traditional lighting architectures allow for independent control of a single lamp, while standards built on bus topologies support independent control of multiple lamps. Note that while DALI and DMX512 can control multiple lamps independently from a single controller, both require additional control cabling.
Traditional lighting architectures have dedicated lines for independently controlling each bulb. In a bus topology, these lines are shared by multiple bulbs, meaning that signals from the controller are received by all the lights. To distinguish between different lights, the controller must be individually bound to each light and assigned a unique address to each.
For example, suppose light fixture A has address 1 and light fixture B has address 2. If the controller sends a message with a destination address of 1, only light fixture A will process the message; light fixture B will not. Similarly, if the message is sent with a destination address of 2, only light fixture B will process the message. Likewise, if the message is sent using addresses, these lines are connected to multiple light fixtures.
Previous systems required users to manually assign addresses to each light (e.g., using DIP switches or dial pads), and then select that address on the controller. However, this method had several drawbacks: 1) setup required additional time; 2) users had to be very careful in assigning a unique address to each device; and 3) if multiple lights were controlled from a single controller, the user had to remember the address number of each light. The current method is more complex and sophisticated: it first lets the controller (not the user) discover newly installed lights on the network, then finds an available address on the network, assigns that address to the light, and finally provides an easy-to-use interface for binding and controlling single (or multiple) lights.
To detect the arrival of a new light fixture on the network, the fixture needs to send a signal indicating its availability. This is best achieved by broadcasting a message so that all controllers on the network are aware of the new fixture. When a controller receives the message, it alerts the user to the addition of the new fixture. If the user decides to control the fixture, the controller sends a binding request message to it. If the fixture is still available for binding, it sends an acknowledgment message. If binding is not possible, it sends a rejection message. Once bound, the fixture will only process messages received from the controller address that bound it.
When a luminaire hasn't been assigned an address, how it receives binding message requests remains a problem. This can be solved by assigning each luminaire a unique 64-bit address (similar to a MAC or physical address). Then, when a luminaire first broadcasts that it's available, it can include its unique address in the message. The controller can then directly send a message to it to bind.
Since a 64-bit address is too long to send normal color control messages, the controller can assign a shorter 8-bit address (called a logical address) to the light fixture after binding is complete. To ensure that the new logical address value has not yet been used, the controller can send a ping message on the power line. If a response is received, the new address is tried again until no response is received.
The user decides to bind only the first available light fixture. Once binding is complete, the controller can begin sending color information to control the light fixture.
Common challenges in power line communication include: the luminaire cannot receive messages from the controller; the luminaire is controlled by the wrong controller.
If the light fixture cannot receive messages from the controller, it is usually due to one of the following three reasons: 1) There is too much noise on the power line; 2) The controller and receiver are not on the same phase on the power line; 3) The distance between the receiver and controller is too far. If the noise on the power line is too great (e.g., from a vacuum cleaner, high-powered appliances, etc.), it is recommended to move the system away from the noise source. If the controller and receiver are not on the same phase, the user should try moving one of them to be on the same phase.
If this is not possible, a phase coupler can be used to bridge power line communication signals on different phases. This coupling can be achieved using a large capacitor or a wireless connection. If the distance between the receiver and controller is too great, an interruptor can be used to retransmit the signal until they reach the desired destination. Some implementations integrate the repeater and the lighting fixture into the same device, thus incurring no additional cost.
Because there can be multiple controllers on the same power line bus, it's possible for a light fixture to be controlled by the wrong controller. This can happen for several reasons, including address allocation and binding mechanisms. If addresses are manually assigned, it's possible for two light fixtures to be assigned the same address. This could be because the user forgot they already used that address, or someone else (such as a neighbor sharing the same power line) assigned the same address.
If the intelligent address allocation and binding method described above is used, all addresses are unique 64-bit physical addresses, making this error impossible. If 8-bit logical addresses are used in intelligent address allocation, the controller will ensure by pinging the network that it will not assign an address that is already in use. Even with intelligent address allocation and binding, it is possible for different controllers to bind to non-target luminaires (e.g., a neighbor binding to a luminaire that a user just plugged in). In this case, the luminaire should have a button that forces it to unbind from the controller, allowing it to freely bind to the correct controller again.
Color control
Color information is typically presented in one of two forms: CIE color coordinates or direct LED dimming values. Direct LED dimming values contain an independent value for the intensity of each LED. For example, if there are three LEDs—red, green, and blue—there are three dimming values. The CIE coordinate system is two-dimensional and can represent any available color in the color spectrum. Together with intensity (luminous flux), CIE coordinates can be blended into direct LED dimming values, depending on the device and the package information of the LEDs used. For example, two red LEDs can emit slightly different shades of red light. The color blending algorithm will take this factor into account so that the resulting color truly represents the desired color.
The type of color information transmitted via power lines depends on the user input, the level of color control precision, and the implementation cost. If the user input is direct LED control, then the direct LED dimming value will be sent. If the user input is a specific color and intensity, then the information type depends on where the color mixing is performed. If the color mixing is completed at the receiver, the CIE coordinates and intensity will be sent.
This is a typical choice because LED package information is usually stored in the luminaire. However, with a PLC , each luminaire can send unique LED package information to the controller, which then stores this information and loads it when performing color mixing. Ultimately, the controller will send the direct LED dimming value.
Advanced color control
As controllers become more advanced, color control can also become more sophisticated, going beyond simply sending a direct color to a single light fixture at a time. Scene setup, fade-in/fade-out, and sequencing are some interesting examples. When setting up a scene, multiple lights can be assigned specific colors, allowing them to emit different colors and intensities (e.g., color gradients) with the touch of a button. During fade-in/fade-out, lights can be instructed to transition to the next color within a specified time. In sequencing applications, multiple lights can change color synchronously (e.g., lighting displays, mood lighting, etc.).
Power line transceivers are typically low-voltage DC-powered ICs. To connect this device to a power line, an amplifier and a coupling circuit are required. The coupling circuit can be modified to support the required voltage range (e.g., 110-240VAC for global home applications, 24VDC for pool lighting, etc.), thus the same power line transceiver IC can be used for any required power line voltage range.
Controller implementation can take different forms, depending on the available physical area and the required level of control. For basic wall switch installations, the lighting control interface can be a simple on/off switch, a dimmer, or multiple dimmers, allowing individual control of the luminaire's color. Additionally, at least one button is used to index available luminaires, and another button is used to bind to a node. LED indicators are also useful for displaying the luminaire's status (available or bound).
Typically, a microcontroller is needed to process these inputs and connect to a power line transceiver. For example, using Cypress's power line communication technology, the microcontroller and power line transceiver can be integrated into a single device that performs input processing, smart bonding, and advanced color control via power line communication.
An innovative approach to replacing traditional mechanical buttons, switches, and dimmers is the use of capacitive touch sensing technology. With this technology, the controller panel can be a flat surface, displaying the control interface using decals. When a user touches a location on the panel, the controller translates that touch into a button press, a switch activation, or a dimming change, the specific function depending on the finger's position. This method provides users with a smooth, clean, and durable interface for controlling lighting fixtures.
Capacitive touch technology can deliver a better user experience by providing two-dimensional control. For example, a controller can detect the x and y coordinates of a finger's touch point and convert them into CIE color coordinates. Capacitive touch technology can also be conveniently used for color control; the panel can be made into a color palette, allowing users to change to any color with a simple touch of their finger.
For more complex lighting control (such as a central home automation system), the controller can run on a PC. In this case, the interface will be a graphical user interface (GUI). The GUI can display all available lights in the home to the user and allow the user to execute more advanced color control schemes. The PC can be connected to the powerline transceiver via USB or wirelessly. Figure 3 shows a feasible example of a controller implementation.
Since a user interface is not required on the lighting fixtures, embedded microcontrollers are typically used to process received messages and control LED colors. Leveraging Cypress's power line communication and high-brightness LED control technology, a power line transceiver and a precision LED color controller can be integrated into a single device. Only an external LED driver is needed to set the LED color. Alternatively, using CypressPowerPSoC technology, a precision LED color controller and LED driver can also be integrated into a single device, allowing for easy connection to the power line transceiver via an I2C interface.
Power line communication (PLC) technology is ideally suited for performing complex LED lighting control, offering low installation costs and eliminating the need for new cabling. Users can control the color, brightness, light variations, or lighting effects of LED lights using traditional wall switches/dimmers, capacitive touch sensors, or PCs. Leveraging advanced fixture discovery and binding mechanisms abstracted from the user, a PLC-enabled lighting control network can be established without the need to remember a number or risk accidentally turning off a neighbor's lights.
