Energy harvesting ambient sensor for tunable white control

Light quality is a very important factor in human wellbeing. In addition to lighting intensity, CCT, the colour of white light, also has a fundamental influence on our mood and performance. The possibility of CCT regulation, called Tunable White, has in recent years become a standard aspect of higher-class lighting solutions. To meet this need, manufacturers have developed a variety of Tunable White control methods ranging from manual and remote control to wired-protocol controls such as DALI.

More complex control devices even offer the possibility of dynamic daylight simulating CCT regulation across a set time period, such as throughout the day, to support the healthy functioning of the circadian rhythm. However, no matter how complex the algorithms of CCT regulation are, they can never facilitate dynamic reactive control based on measured ambient CCT values unless there is a sensor to provide feedback measurement.

The advantages of using ambient light sensors to regulate lighting intensity are well known. iLumTech has already developed the innovative DALI Ambient Sensor, which is capable of sensing not only ambient light levels but also ambient CCT values. The DALI Ambient Sensor is directly connected to a DALI bus, making it possible to configure it directly to measure ambient lighting intensity and CCT values and, if desired, additionally regulate the illuminance and CCT output of connected luminaires.

However, such wired connection restricts the mounting of the sensor to ceilings as the presence of DALI wiring would be inappropriate and limiting in any other relevant location, such as on a table top. Ceiling mounting also means that sensors can only be placed in one static location, necessitating the use of several sensors to cover larger areas, even if they are not used regularly. What’s more, measurements taken by statically located sensors can be negatively affected by objects and surfaces under the sensor as it only measures reflected light, especially if those objects and surfaces have non-ideal reflectivity.

This issue can, however, be eliminated by proper sensor calibration. Another limitation of ceiling mounted sensors is that they measure light from luminaires reflected from a range of surface colours, which has a modified spectrum due to reflection. To achieve accurate measurement data about the light emitted from luminaires, it is necessary that sensors sense it directly - in other words, the ideal location for an ambient lighting intensity and CCT sensor is on the table top. In answer to this dilemma, iLumTech have developed a wireless ambient lighting intensity and CCT sensor. The solution is wireless both in terms of communication and power supply.

We live in an era of smart and environmentally responsible technologies, a trend becoming central in the lighting control industry. Every light source represents a natural source of energy, energy that is almost entirely wasted. iLumTech has combined its existing Ambient Sensor technology with smart technologies to bring to the market the Energy Harvesting Ambient (EHA) sensor, which is powered by a PV cell.

The size of the cell is a compromise between optimised harvesting and practical application. Depending on the location of the sensor, it is able to make up to five measurements per minute, with the data needing to be read by a control device to facilitate lighting regulation. The Bluetooth Smart (Bluetooth 4.1) interface is used for wireless transmission of the measure data. As there is not enough energy supplied by the PV cell to establish connectivity, the data is broadcast transmitted using advertising mode. Now that Bluetooth Smart is becoming a standard feature of smartphones and tablets, the data transmitted by the EHA sensor can easily be read by almost any Android device with the appropriate app installed.

To facilitate control, iLumTech has developed BlueBridge and interface between Bluetooth Smart and standard DALI buses. BlueBridge is powered directly from the DALI bus and so does not need any power source. Using BlueBridge allows for complete control via a DALI installation, even of type eight devices (colour control). The GUI is an app that runs on Android devices that support BluetoothSmart. The control features of BlueBridge can be used generally for any type of DALI installation where the range of Bluetooth Smart is sufficient (up to 50m without obstacles).

Furthermore, BlueBridge is fully compatible with the EHA sensor. Using the app, users canconfigure a simple regulation loop that reads data from an EHA sensor and control Tunable White luminaires (defined by group addresses) using BlueBridge as an interface with the DALI bus. The EHA sensor is a pocket-sized solution for accurate and realistic measurement of ambient lighting intensity and CCT values at task areas in offices and homes. In combination with BlueBridge and compatibility with Bluetooth Smart, it allows for comfortable data presentation and wireless control of DALI installations (exclusive ofthe wiring of the luminaires).