APPLIANCES AND EQUIPMENT

Energy-efficient Lighting Control

Energy-efficient lighting control based on a variety of technologies have been proven to reduce lighting energy consumption in commercial and industrial buildings by up to 70%. Examples of the most common types of lighting controls include occupancy sensors, time scheduling, bi-level switching, and dimming technology. They can be used solely or in combination depending on the lighting requirement.

Dimming technology became more popular in recent years. Analogue dimming was the first attempt to dim lamps (such as fluorescent lamps) by reducing power of ballasts in electromagnetic type. It involves the use of a 1-10 V DC control voltage and a potentiometer (either rotary or slider type) that has a dimming range down to 1 or 3%. However, when the wiring distance is long, the voltage drop is usually significant and makes it inaccurate. Also, its proportional scale nature does not reflect true sensitivity of human eye.

Schematic diagram of analogue dimming (source: Ansell, UK)

Following the development of micro-processors and network standards such as LON, EIB, C-Bus etc., dimming control is now moving towards the digital technology that the control system sends the data bit for the level required. The ballast requires a digital signal from an external source, via a digital serial interface (DSI) to instruct the ON/OFF and dim operation.

Typical equipment for intelligent digital control using DSI.

Digital signal simply gives the lighting level required. The control of ballasts is by a 2-wire bus at the voltage of 12V and universal polarity. It allows precise commands, disturbance free signal to all ballasts based on a logarithmic scale (127 log(%) + 1) to reflect true sensitivity of human eye.

Eye sensitivity dimming curve

Proper control using appropriate equipment can significantly reduce the energy consumption of lighting systems. One of the examples is the Digital Addressable Lighting Interface (DALI), which is a digital communication standard (an addition to IEC60929) that guarantees the exchangeability of dimmable electronic ballasts from different manufacturers. It provides a simple and digital way of communication among intelligent components in a local system in a way that is free of interference. DALI provides simple wiring of control lines, no separate conduit/trunking is needed. It allows control of individual units (individual addressing) or groups (group addressing). Also, simultaneous control of all units is possible at any time. The figure below shows a typical configuration of a DALI control system.

Typical DALI lighting control system

With the DALI, the lighting system in buildings can be designed to suit various dimming and functional requirements via Central Control and Monitoring Systems.