Electric Lighting Controls PDF

9. ILLUMINATION SYSTEM CONTROLS 9.0 IMPORTANCE OF CONTROLS Controls are switching devices which may manually "or automatically activate the lighting system. These may take the form of "on-off" control or controls which vary the power input to the system in accordance with actual nee...

9. ILLUMINATION SYSTEM CONTROLS 9.0 IMPORTANCE OF CONTROLS Controls are switching devices which may manually "or automatically activate the lighting system. These may take the form of "on-off" control or controls which vary the power input to the system in accordance with actual needs. Controls cover a broad range of devices, each suited to a particular system's requirements. These requirements must be established prior to selecting any control device. To save energy, two factors may be varied : Power allocated to the lighting system Length of time that power is used. The length of time that power is 'ON' is dependent upon the needs of the occupants and the effective use of controls, 9.1 WHICH LIGHTS SHOULD BE CONTROLLED? When the building operation requires round-the-clock use of lighting (such as a computer centre which operates 24 hours a day) extensive controls will be of little value. However, should the function of a building permit all or part of the lights in any particular space to be turned 'OFF' at times, an opportunity may exist to save electricity through controls. When lamps are switched 'on' and 'off’ their life may be reduced slightly so that in the past when electricity was cheap, lamps were never turned off. Now, lamp replacement casts are generally much less than the value of the electricity saved so that such replacement costs are no longer considered in energy studies 9.2 HOW TO SELECT A CONTROL SYSTEM A control system must be based upon the use of the space. Where it is intended that the occupants will control their own lighting, the control devices must be located conveniently. Some of the examples are given below To obtain a greater degree of control in large rooms, individual work areas may be switched separately, This would permit some people to keep lights in their area 'ON' while adjacent unoccupied areas may have the lights ‘OFF’. In rooms with more than one exit, it may be desirable to locate a control device at each entrance. This may increase the use of the control devices since the occupants can turn the lights off, when leaving from either exit. 9.3 VARIOUS CONTROL SYSTEMS The following are the some of the types of controls employed to save electricity. 9.3.1 Circuit breaker control The most common 'ON-OFF' control of lighting is by branch circuit breaker. This circuit breaker function, however, is not to work as a switch but to protect the circuit against overload. The wear and tear of repeated use is not intended by the manufacturer. Moreover, the building panel board is often inaccessible to the occupants of the space being served, depriving them of control over their own use of the lighting. 51 9.3.2 A.C. Snap Switch The A.C. Snap Switch is wired directly into the power Circuit supplying the lighting fixtures. The switch provides manual 'ON-OFF' control by closing or breaking the power circuit which supplies electrical energy to the fixtures The switch is rated for operation at the power line voltage and to carry and interrupt maximum branch circuit current. The A.C. snap switch is a low cost, simple device that may be installed in any location, where manual 'ON-OFF1 operation is desired. Its usefulness in retrofitting will depend upon the extent of rewiring involved. Since the A.C. snap switch is manually controlled, it depends entirely on the occupants of the space to realize electricity savings. 9.3.3 Low Voltage Remote Control The low voltage switch is not designed to directly switch the power to the fixture, rather it does so indirectly via control of a relay.. A power supply transformer is needed to provide control power to operate the relays. Relays can be controlled automatically by time clocks, photocells or computers. Low voltage remote control permits greater flexibility than A.C.Snap Switches. It provides the ability to control loads from great distances, a number of different loads from one location and one load from multiple locations. When controlled automatically, local manual overrides may by provided to allow for overtime use. For application in existing buildings, the higher equipment costs of the low voltage systems may be offset by lower wiring costs. 9.3.4 Time clock Time clocks are automatic controls which may turn lights 'ON-OFF' at a preset time according to a predetermined schedule (usually a seven day schedule). Time clocks may also be utilised to turn exterior lights 'ON' and 'OFF'. They may also be used in conjunction with other control systems, such as low voltage control, to control lights throughout the building. Although the 'ON-OFF' schedule may be changed, the time clock is not generally intended for use when requiring frequent schedule changes. 9.3.5 Timed switches Timed switches may be used manually to turn lights 'ON' and will then automatically turn the lights 'off after a predetermined time interval (available from 5 minutes to 12 hours). Timed switches are useful in all rooms which are not in continuous use (such as toilets) and in which occupants may neglect to turn lights 'OFF’. Timed switches are installed in a manner similar to the A.C. snap switch. 9.3.6 Photo cell controls Photo cells are devices used to sense light. Based upon the level of light, the photo cell will open or close a relay or automatically adjust a dimmer setting. Photo cells can be useful for control of lighting systems based upon quantity of available light. The photocell, however, must be cleaned periodically to assure proper operation. 52  A common application of photocells is with exterior lighting systems. In this application, the photocells senses sunset and turns the lights 'ON' and then senses sunrise to turn the lights 'OFF'. The photocell may be also used with other control devices such as the dimmer control. 9.3.7 Dimmers Dimmers are used to vary the quantity of illumination. Their operation may either be manual or automatic. Dimmers may be useful electricity.conservation devices. A photocell can sense any available natural light and automatically reduce the output of electric lighting system, while constantly maintaining adequate lighting. There are dimmers for incandescent lamps, fluorescent and HID. They are not interchangeable. 9.4 MAINTENANCE Once installed, the efficiency of a light source depends to a large extent on how well the fixtures are maintained. A lamp that produces 20 lumens per watt when installed may actually distribute only 10 lumens when covered with dust. The reflecting value of fluorescent fixtures is directionally correlated to their illuminating ability, and their tendency to collect dust may be countered by frequent cleaning. Bulbs should be replaced when they first begin to dim, before they completely burn out. When lighting systems are over designed and generate too much light initially, a 15 percent depreciation in output was neither noticed nor important. Now with the high cost of power, closely designed energy efficient systems cannot tolerate dirt accumulation. Lighting system maintenance procedures are relatively few but most effective. The following procedures are recommended. Lamps should be wiped clean at regular intervals to assure maximum efficiency. Lamps which are exposed to an atmosphere with substantial amounts of dust, dust, grease, or other contaminants should be cleaned more frequently than lamps in relatively clean atmosphere. Cleaning of ceilings, walls and floors should be done frequently to improve reflective qualities. In rooms or areas where natural day light is used to maintain light levels, washing of windows should be done frequently. If any renovating or painting is planned, the use of white or light colours will improve light quality. The choice for walls and ceilings has a surprising effect on the efficiency of the lighting system. Light colours reflect more light than they absorb. Dark colours absorb more light. A given lighting system may be as much as twice as efficient in a light coloured area as it is in a predominantly dark one. Repainting walls and ceilings should be considered in conjunction with other measures like lamp removal and replacement with energy efficient lamps etc for improving lighting efficiency. In some cases the owner may be able to maintain existing light levels by brightening his colour scheme while removing lamps or using lower wattage lamps. The colour selected does not necessarily have to be white but may be any lighter (more brilliant) hue. -------------------------------------- 53