Big cities are changing over to LED lights for illumination of their streets. They find this to be a smart solution in terms of cost-reduction and efficiency. STMicroelectronics is taking an important next step by adopting LEDs for street illumination. They are doing this in conjunction with smart power supplies that turn the LED street lamps into intelligent devices. For example, the streetlamps reduce their brightness as the sun rises while gradually increasing their brightness with failing daylight. They also communicate with the smart grid in their effort to reduce the power consumption.
To avoid losses and manage electricity consumption smartly, STMicroelectronics is using LEDs that are dimmable and connected to smart grid systems. Microcontrollers drive the LEDs, and the system avoids the power losses commonly associated with non-optimized management of power such as with the use of incandescent bulbs and other forms of commonly utilized lights.
STMicroelectronics present their new solution in the form of a demo board based on STLUX385A, a digital power controller. Using a proprietary power conversion protocol, the controller drives a row of LEDs for the smart-lighting applications. DALI forms the core of the new STsystem for smartly driving the LED row.
DALI or the Digital Addressable Lighting Interface, is also standardized as IEC 929, and is a new interface for controlling lighting as defined by the lighting industry. The DCM or the DALI Communication Module generally implements DALI protocol. DCM is a serial communication circuit designed especially for controllable electronic ballasts – the device or circuit that provides the required starting voltage and operating current for the LEDs.
LEDs are different from CFLs and incandescent bulbs. LEDs require a supply of constant current. They start emitting light as soon as their forward electric threshold voltage is reached. Effectiveness of the illumination provided by a string of LEDs depends on the product of the current and the voltage applied to the string, and this must be stable in time.
HF fluorescent ballasts use the DSI protocol, and DALI is a step further. Unlike DSI and other 1-10V devices that address and control devices in a group, DALI can address each device separately on a segment of a data cable. Therefore, for achieving similar control functionality, DALI requires a simpler wiring topology as compared with DSI or 1-10V devices.
Devices that DALI can control include, apart from LEDs, wall switches, gateways to other protocols, motion detectors, PE cells, low-voltage transformers and HF ballasts for Fluorescent tubes. A single DALI network can address up to 64 DALI devices. When sites require more than 64, multiple separate DALI networks are established, each limited to 64 devices. DALI gateways then link these separate networks together, forming a data backbone running a high-level protocol, typically, DyNet from Dynalite.
Implementation of DALI facilitates equipment from different vendors to the integrated easily. This reduces the installation costs drastically, offering a finer granularity of control for a given price. However, DALI still does not totally remove the need for a data cable connect to fixtures. It also does not reduce the time required for programming and commissioning the lights. Additionally, unless extra equipment is used, DALI does not help to save the maximum possible amount of energy.
