Industrial Interior Lighting PDF

7. INDUSTRIAL INTERIOR LIGHTING 7.0 INTROOCUTION Industrial lighting covers an extremely wide range of different working interiors and work tasks from small workshops to huge factory halls and from the fine precision work often carried out in the former to the heavy industrial tasks...

7. INDUSTRIAL INTERIOR LIGHTING 7.0 INTROOCUTION Industrial lighting covers an extremely wide range of different working interiors and work tasks from small workshops to huge factory halls and from the fine precision work often carried out in the former to the heavy industrial tasks generally associated with the latter. The design of a work place may make the task of lighting the workplace easy; on the other hand, there may be obstructions formed by awkwardly-shaped machines to contend with. Again, the work itself may be easy to light, or it may impose certain special requirements on the lighting: such as, for example, freedom from producing reflections or, conversely, the deliberate creation of these to bring out surface detail or reveal imperfections in surface finish. Careful attention has to be paid to these and other aspects of lighting, which includes the need to study the cost effectiveness of the various lighting systems available. This can maximise productivity, minimise accidents and save on operating costs, whilst also helping to promote the comfort and well being of the worker. 7.01 GENERAL Protection and safety In humid areas, luminaires affording protection against the ingress of water are needed, while in dry environments, the luminaires will have to be dust protected. In either case the IP classification of the luminaire employed will have to be considered In areas where lamps or luminaires can be touched, electrical safety is specially important and in areas where explosive gases, vapours, or volatile liquids may be present, the luminaires will need to be of the type suitable for use in hazardous areas. Environmental requirements When called upon to operate in areas where the ambient temperature is very low, as in frozen food plants or cold storage ware-houses, special care should be taken to avoid problems with lamp starting and light output. This is more critical with tubular fluorescent lamps than with most high-intensity-discharge lamps. With incandescent lamps, this problem does not arise. In areas where the temperature in the vicinity of the luminaires is high, as in foundries and steel mills, it is important to ensure that the working temperature of the ballasts is not exceeded. 7.02 LIGHTING LEVELS Recommended illuminances for various interiors and tasks are given in IS: 3646 - (Part I).1992. The illuminance values in the table are maintained illuminances. The mean value of the illuminance at the task location must not be lower than the illuminance indicated, irrespective of the age of the installation. Those tasks not covered by the above tables must be dealt with by experiment or by comparison with a task of a similar nature, the recommended illuminance for which is known. 7.03 LIGHTING SYSTEMS There are three systems of lighting used in industrial interiors: general lighting, localised lighting and local lighting. Only general lighting and localised lighting may be used on their own. Local lighting is a back-up system, which may be used to supplement the main lighting as and when required. 39 General lighting It is designed to produce a more or less uniform illuminance on the working plane throughout the area involved. Uniformity is generally considered adequate if the ratio of the minimum to the average values at any given work position is not less than 0.8. Lighting with this degree of uniformity will generally ensure complete freedom in the placement of machinery and work benches. It is achieved by employing a more or less regular array of overhead luminaires. The choice between tubular fluorescent and high pressure or metal halide lamps for the general lighting will be influenced primarily by the mounting height available. This can, of course, vary considerably from one type of-industrial interior to another. For the purposes of lighting design, it is convenient to divide mounting heights into four groups according to the type of building involved. Mounting height (M) Typical industrial premises 2.5 - 3.0 Multi-storey office-type building 3.0 - 4.0 Single or multi-storey factory building 4.0 - 7.0 Single storey factory building Above 7.0 High-bay factory hall. Mounting height 2.5 - 3.0 M Many modern light industries are housed in multi-storey buildings that architecturally have much in common with office blocks. These generally have smooth, white ceilings, which can serve as extended reflectors for the purpose of obtaining a better diffusion of the light and an improved luminance pattern. Just as in offices, therefore, the best compromise between good lighting quality and efficiency in use is offered by fluorescent lighting. Where the layout of the work-stations is not known in advance or is subject to change, the overhead luminaires can either be arranged in equally-spaced rows or in a regular grid pattern so as to produce the desired lighting level throughout the interior. Energy efficient T5 luminaires are ideal for this purpose. On the other hand, where the work lay-out is permanent, it is possible to employ a rather more economical asymmetrical lighting arrangement that provides lower lighting levels in circulation areas. Because of the limited mounting height available, special attention should be paid to the control gear, especially where VDU screens are used. This means employing well- screened luminaires. And where rows of luminaires are employed, these should run parallel to the windows and at right angles to the viewing direction of the workers. Mounting height 3.0 - 4.0 For mounting heights upto 4.0 m, lighting employing reflector luminaires housing tubular fluorescent lamps again normally offers the best solution. The luminaires are usually arranged in continuous or broken rows running parallel to the windows and the viewing direction and at right angles to the rows of work benches or machines. This both prevents troublesome shadows from being cost on the visual task and reduces the possibility of light being reflected into the eyes of the operators. The alternative arrangement in which the lines of luminaires with well shielded lamps run at right angles to the viewing direction gives an overall impression which is usually more restful It is not always possible, however, to gain the benefits of both these arrangements simultaneously. Usually, good viewing conditions at the working plane are more important than a pleasing 40 overall impression. Modern energy efficient T5 fittings of 4 feet length or 2’length can be used. Surface mounted suitably screened fittings can be used to limit the glare. In situations where the relocation of working areas is usual, the use of trunking systems containing the wiring for the luminaires is recommended. Single or twin-lamp luminaires can then be positioned on the rails of the system to provide the appropriate amount of light as and when required. Mounting height 4.0 - 7.0 Single-storey industrial buildings of this height usually have a flat or saw tooth- shaped roof pierced by window openings, or side windows high up in the walls. Whatever the kind of work, however, it is necessary to add artificial lighting, even during daylight hours. The usual solution is to employ reflector type fluorescent lamp luminaires in rows running either at right angles or parallel to the windows. For the lower roof heights these are mounted against the ceiling or the underside of the roof structure, while at greater heights, they are suspended from the roof. Dimmable high-frequency fluorescent lighting with day- light-dependent control can be an economic solution where day light levels are high. Energy efficient T5 luminaires are ideally suited as fluorescent lights for this purpose. Modern reflector type (4Nos x 2’T5) are also suited with equal spacing. Uniformity factor also improves with the use of more number of 2’T5 fittings. An alternative to tubular fluorescent luminaires where the mounting height is about 6 metres is to employ a lesser number of more powerful metal halide lamps spaced farther apart. This leads to major economies in installation, operation and maintenance. However, care should be taken to maintain an acceptable lighting uniformity and to avoid the harsh shadows produced by employing too few light points. The lamps which can be used are of three types: high-pressure mercury, high pressure sodium and metal halide. However due to poor colour rendering qualities, presently high pressure sodium lamps are not used except in general ware houses where colour rendering is of no importance. Even though high pressure mercury lamps can be used, metal halide lamps are ideally suitable due to their better luminous efficacy and better colour rendering index.. These lamps are housed in so-called high-bay reflector luminaires, the reflector of which, provides the desired degree of light concentration and also serves to shield the lamp from sight at normal angles of view. This shielding, together with the fact that the luminaires are normally well above the normal line of sight, means that glare is easily avoided. Narrow-beam luminaires of this type are employed to advantage in those interiors where good light penetration is needed in order to illuminate floor areas between tall, closely placed items of machinery, piles of packing cases, and so forth. Wider beams are used in those areas where tall vertical surfaces, such as control panels and storage racks, have to be clearly visible. Mounting height > 7.0 M Where very high single-storey structures are concerned the light sources usually have to be mounted high up. This is done to keep them clear of the guide rails of traveling cranes or similar machinery ,because the equipment in the workshop is very tall. 41  The vast majority of installations employ rows of conventional high-bay luminaires. These have a symmetrical, narrow beam or wide light distribution, and house high-intensity (HID) lamps (metal halide, high pressure sodium or high pressure mercury) of upto 400W. Metal halide luminaries are best suited for this purpose in most of the workshops and industries due to their better colour rendering. The flood light, with its more sophisticated optics capable of producing a symmetrical light distribution and housing HID lamps of 1 KW or more, comes into its own where it is necessary to create high illuminances on very high vertical surfaces. From the technical as well as from the economic and maintenance points of view, all these light sources are well suited to these types of installations. Localised lighting On those interiors where the arrangement of the work position is permanent, the use of localised lighting in preference to general lighting can sometimes lead to advantages in terms of increased worker comfort and reduced maintenance and energy costs. The luminaires should be concentrated relatively low above the work areas so as to provide the higher illuminances at these points whilst providing at the same time an adequate level of lighting in the gangways where orientation is required. Special care should be taken to ensure that the luminance of the environment as a whole does not suffer due to the limited amount of general lighting. Local lighting The requirement for certain types of task with regard to lighting level and lighting quality can be so stringent that it is neither technically feasible nor economically viable to satisfy these requirements by employing a system of general lighting alone. Where localised lighting is also unable to provide a solution, the answer is to install local lighting. Local lighting is designed to illuminate the area occupied by the visual task, and its immediate surroundings. Local lighting is also employed to increase the illuminance at work positions that, due to the presence of obstructions (including the worker himself), are not sufficiently well lighted by the general lighting. From the point of view of maintaining the desired brightness balance in the area of a visual task and in the visual field beyond it, it is advisable to look upon local lighting as a useful supplement to general lighting but never as a substitute for it. 7.04 SPECIAL TASKS IN INDUSTRY Manufacturing processes often consist of tasks which, for economic or technical reasons, require special visual attention. In order to achieve optimum visual conditions for carrying out of a particular task, the task has first to be analysed. In most cases, the best way to determining the actual visual requirements is by attempting to carry out the task oneself. It will then soon become clear whether better lighting is necessary or not. Once the visual requirements are known, the main problem is solved. The next requirement is usually the creation of the necessary contrast between the details to be distinguished and the background agSainst which they are to be seen. 42  For certain manufacturing processes and for the inspection of certain products, the normal general lighting system does not meet up with these requirements. In such cases, special solutions have to be found. Some examples of certain tasks that call for the use of additional lighting aids are listed in the table given below: Task Lighting aid Inspection of small objects Such tasks can often be simplified or the assembly of minute by the use of an illuminated mechanical parts or magnifying glass. electronic components Checking of dimensions. This is often done by projecting a much enlarged image of the object on to a screen. Inspection of machined parts The use of stroboscopic lighting while they are in motion. may offer a very satisfactory solution. The frequency of the stroboscopic flash can be adjusted such that the object illuminated appears to be stationary. Inspection of certain Objects made from certain materials, such as materials. glass, can best be inspected under monochromatic light. Low pressure sodium lamps provide such a light. Table: Examples of Industrial lighting aids -------------------------------------- 43