Lighting Systems: Good lighting is becoming increasingly recognized as an important aid to management in achieving high productivity and in providing satisfactory working conditions for employees which will able them to work efficiently, accurately and safely with minimum fatigue.
Basic requirement of Lighting system in industries:
Make the task easy to see:
Besides providing sufficient light on the work, it is important to make sure that the illumination is of suitable quality i.e. it should contain both diffuse and directional components since his combination produces the soft shadows which reveal the shape and position of objects and also helps to crate the reflected highlights which revel the shape and texture of shine surfaced articles. On the other hand, troublesome reflections: which may obscure details in the task must be avoided.
Provide comfortable seeing conditions:
Glare and gloom must be eliminated by housing lamps inside will-designed lighting fittings which adequately screen them from view and also distribute some light to the ceiling and upper walls of the room.
Correct spacing and placing of these fittings with respect to the work is often of great importance: moreover; than main interior surfaces of the room such as the ceiling, walls, plant, etc. must be finished in suitable light-reflecting colors.
Keeps the installation in good working order:
In designing an installation the need for future maintenance must not be over looked. It is therefore necessary to choose equipment that will be easy to service and also provide safe and easy means of access, poor seeing conditions case inefficiency, spoilt work and accidents, money spent on an installation complying with all the requirements for good seeing is an investment which not only ensures better and safer working conditions but which also helps to promote maximum productivity.
Choice of illumination level:
It is essential to remember that whilst doubling the illumination on a badly under lit task will produce a substantial improvement in the efficiency with which it can be performed, further doubling and redoubling of this illumination produces a smaller and smaller improvement each time. In other words, the curve tends to flatten. out at a performance level, which no further addition to the illumination can improve.
Selection of lamps for Lighting Systems:
The first step is to choose between the three main types of lamps : incandescent filament tabular florescent and colors corrected mercury vapor lamps (sodium vapor lamps are seldom suitable for interior lighting on account of their poor colors rendering properties.).
Candescent filament lamps:
The simplicity, compactness and versatility of this type of lamp makes it suitable for man application; but for ordinary general lighting purposes, it is comparatively short life and low lumen-per-watt efficiency put it at a disadvantage as compared with the other two types.
Suitable applications as follows:
- Where artificial lighting only occasionally required; (e.g. now and then on dark afternoons in winter, or in seldom visited store rooms);
- Where space restricted (e.g. in small adjustable local lighting units mounted on a machine tool);
- Where a powerful concentrated beam of light is required.
Tubular florescent lamps for Lighting Systems:
The high efficiency and long life of these lamps makes them particularly suitable for general lighting purposes, and it is possible to obtain lamps with particularly good colors rending properties when this characteristic in needed.
Suitable applications are as follows:
- Where artificial light needed regularly every day;
- Where an elongated light source needed;
- To replace and incandescent lighting scheme when the illumination level must be increased but the wiring is already fully loaded.
- Where good colour rendering particularly important;
Mercury vapor lamps for Lighting Systems:
For interior lighting purposes, the “colors-corrected” variety with a fluorescent powder on the outer jacket should be used. These have colors rendering properties, which are quite good enough for most industrial lighting purpose. The main advantage of the mercury vapor lamp is that whilst its lumen-per-watt efficiency approaches that of the tabular fluorescent variety, it is more compact and also available in much higher wattage sizes.
In a large, loft factory building where widely spread high wattage fittings can be used without making the illumination on the workplace un even;
For exterior lighting of storage areas, docks, roadways etc., if color rendering is unimportant, ordinary uncorrected mercury lamps (and sodium lamps) may be used,
Choice of lighting fittings:
All types of lighting fittings require cleaning at regular intervals and it is particularly important to make sure that this task can be performed easily and safely. In the case of hand lamps, local lights on machines, and other equipment that can actually touched by the worker, electrical safety particularly important and low voltage gear (under 50 volts) recommended. When the atmosphere may contain explosive gases or vapors suitable flame-proof fittings may be used; special types of fitting are also available for use when the atmosphere contains corrosive vapors.
Glare control for Lighting Systems:
Glare mainly caused by light emitted at or near the horizontal. Lamps must therefore screened from view throughout this critical zone; in practice, this achieved either with opaque shades and louvers, or with translucent diffusing material, which cuts down the brightness of the unit to more comfortable proportions. When visual tasks are difficult and prolonged glaring lighting units can produce much unnecessary and fatigue.
Unless the ceiling or roof separately lit, suspended unit should always emit a proportion of their light upwards. This light diffusely reflected from the roof (which must. of course have a suitable light color). Besides eliminating the gloomy” tunnel effect” which occurs when overhead surfaces left shrouded in darkness, this arrangement helps to produce optimum seeing conditions. The diffuse light (from the roof) and the direct light( from the fittings) combine to create the soft shadows which best reveal the shape and relative position of objects;
Typical general lighting units for Lighting Systems:
Industrial type troughs and shades:
These should preferably have small slots, which allow at least 10-15% of the light to escape and upward direction. This will be sufficient to dispel overhead gloom, and also ensure adequate ventilation of the fitting, thus helping to prevent dirt from collecting inside.
Totally enclosed diffusing units:
Units of the type provide high quality lighting, and the incandescent variety are far the best type to use when an office is to be lit with incandescent lamps. The fluorescent version gives comparatively. Little upward light, and for this reason should ceiling-mounted rather than suspended.
Louvered fluorescent units:
Theses may have metal or diffusing ones. If from the a affected by airborne dirt than totally enclosed types.
Director-indirect units for Lighting Systems:
The essential feature of this type of unit is the pair of large aperture above the lamps. large slots allow same 40% of the available light to escape to the ceiling and for this reason convenient to refer to them as “40/60” fittings (this being the relative, proportions of upward an downward light). Being made entirely of metal, such fittings are frequently cheaper than the enclosed large slots allow same 40% of the available light to escape to the ceiling and for this reason convenient to refer to them as “40/60” fittings (this being the relative, proportions of upward an downward light). Being made entirely of metal, such fittings are frequently cheaper than the enclosed diffused type.
Bare fluorescent lamps units:
If the room is very small (so that all lamps are well up; out of the field of view of the occupants they can safely used. They can also sometimes employed in long narrow room where everyone views the units more or less and end on.
In offices with low ceilings it is often necessary to recess the lighting fittings; leaving the mouth flush with the ceiling. In such case light from the fittings can only reach the ceiling by reflection; and the system is most likely to be satisfactory when the room is mall in size; with a light decoration scheme; or when the general illumination is reasonably high (at least 50 m/ ft2, or 500 lux).
Luminous and louvered ceilings:
In general, a louvered ceiling gives better visual conditions than a luminous ceiling made of continuous sheets of diffusing material. A uniformly bright luminous ceiling tends to produce excessively diffused lighting; which is apt to make the interior look dull unless the illumination level is particularly high.
Incandescent lamp units for Lighting Systems:
Deep shades should used and a black band; should preferably painted round the inner edge of adjustable shades, which may be set at an angle. Handle lamps should be of a well-designed, strongly constructed type. The lamp socket should properly surrounded and insulated for the wire guard.
Low-voltage incandescent lamps are more efficient and robust than equivalent mains voltage types. They safe to use, provide that the supply transformer properly insulated and earthed; preferably at the center point of the secondary winding. In particular dangerous situations; (e.g. inside a metal tank or boiler shell) center-point earthling to reduce maximum potential to earth to 16 volts)
Flores cent lamp units:
Troughs should mounted either low enough to ensure that; all bright surfaces completed hidden or high enough to ensure; that they are well outside the normal field of view.