Purpose of lighting:
- We receive 80% of information through our eyes.
- To increase work efficiency proper illuminations are to be arranged. Better lightings pay off through higher efficiency.
- It is the management’s responsibility to arrange proper lighting. Sufficient illuminations should be arranged.
- As our age increases the eye-sight power diminishes.
- The light may be natural or artificial.
- Change in the visual background can enable to work more efficiently.
- The purpose and benefits of good illuminations are many. There are 3 groups of working conditions:
- Physical or environmental i.e. illumination, ventilation, noise, atmospheric conditions, etc.
- Relating to time i.e. hours of work, rest, etc.
- Relating to the social situation within which an individual works. Light and color affect human efficiency, accident possibility, and his general well-being, morale,e, and fatigue. Light regulates various psychological functions within the body and poor light adversely affects health.
Lighting requirements depends on:
- The nature of work.
- The efficiency of the worker’s sight.
- A working environment where works are carried.
- In a factory machine shop, workers require less light than a watchmaker.
- An old man requires more light than a young boy.
- As per the study, 37% of workers wear spectacles.
- worker’s eyesight medically checked for color blindness also.
Benefits of good illumination:
|Type of work||Illumination (lux) OLD||Illumination (lux)NEW||Performance increase (%)||Rejects decrease. (%)|
|1. Composing room (print)||100||1000||30||18|
|2. Cotton spinning mill||170||750||10.5||39.6|
|3. Wood manufacturing work||300||2000||16||29|
|4. Screw sorting||100||1000||10||22|
|5. Telephone assembly||150||250||36||57|
|6. Tool company||500||2000||10||20|
The phenomenon of lighting and safety:
- Make use of natural light: Natural light is best and cheapest than the arrangements of artificial light. We can get natural light through windows and roof openings. In order to get more illumination through windows, the window glass panel must be kept clean and closed. Lack of cleaning can result in 10% to 20% of light.
- Avoid glare: glare means especially bright light points or areas within the vision. Glare reduces the quality and productivity and also discomfort to the eye that is eye fatigue. There are two types of glares. One is direct glare and the other is reflected glare. To reduce the glare framework use blinder, curtains, etc.
- To avoid glare, no naked bulbs or tubes should be in the view of the worker. Deep shades and shields should be engaged. The inside of the shades should be painted a dark color.
- As per Factory Rules, level of illumination prescribed at the working plane where the mounting height of the light fitting is more than 7.5 meters from the floor, the general illumination should be not less than 10 lux to 30 lux where the work is actually being done.
- As per Indian Standards IS: 364:1966 ‘Code of practice for interior illumination, the level of illumination prescribed in various factory areas are:
- Canteens 100 lux
- Clock room 100 lux
- Entries, corridors, stairs, etc. 100 lux
- Rough work 150 lux
- Medium work 300 lux
- Fine work 700 lux
- Very fine work 1500 lux
Types of glare:
- Disability glare: This type actually reduces the ability. Sometimes the worker may not recognize this condition but his output will suffer. This type of glare is more disturbing to elderly people.
- Discomfort glare: This is from the display of bright lighting and depends upon the brightness and size of the source.
- To avoid glare from local lighting units, they should be mounted with the lower edge of the shade either below the horizontal line or about the line at 15 degrees.
Types of light sources
Fluorescent lights :
- At least 3 times more efficient than the flammable lamps.
- Low brightness, minimum glare, and shadows.
- Color rendering close to daylight.
- Produce much less heat.
- Longer life.
- Linear form is more suitable for lighting continuous areas.
Selection of light sources are also depends:
- Types of application.
- Atmospheric conditions of industrial interiors and/or exteriors.
- Surface features.
- Initial outlay.
- Running cost.
- Ease of maintenance.
Selection of lighting fittings should consider
- Luminance or brightness.
- Design of luminaries to avoid glare and shadow under normal seeing conditions and to produce the highest initial and sustained light outputs.
- Mechanical construction can be conveniently installed and repaired.
- Suitability for normal use and special areas like indoor or outdoor and hazardous areas.
- The direction of incidence of light and shadow effect.
- Colour appearance and color rendering.
- Its contrasts with the background.
- The duration of the visual work.
Principles of good illumination:
Meaning and measurement: Light is the electromagnetic visible radiation (waves) within the range of 400 to 700 nanometers. 1 nanometer (1 nm) is 10 to the power of 9 meters. Luminous radiation exerts a certain influence on the nervous system, pulse rate, intensity of certain metabolic reactions, and the psychological state of human beings. For adequate lighting, the quantity and quality of illumination, are essential.
Conditions for good lighting are:
- Adequate illumination.
- Avoidance of glare.
- Avoidance of shadow.
- Uniform lighting.
- Appropriate contrast.
- Appropriate color contrast.
- Better color rendering.
- Avoidance of flicker.
- Adequate illumination needs sufficient quality of illumination necessary for avoiding discomfort to the worker and the un-due strain on the eye.
- The quantity or intensity of illumination is given by luminous flux, luminous intensity, and reflection factor.
- The quality of illumination depends on three factors – diffusion, distribution, and color value. Diffusion is the process of reflection of light.
Avoidance of glare:
- Glare is of two types – direct and reflected.
- Direct glare comes directly from the light source to the eye and depends on the position of the light source and on the contrast in brightness between the light source and its background. It can be avoided:
- Reducing the brightness of the light source enclosing by bowl reflector).
- Reducing the area of the high brightness by installing louvers below the light source).
- Increasing the angle between the source of glare & the line of vision).
- Increasing the source of glare by lessening contrast.
- Reflected glare is that which comes to the eyes as a reflection of the light source from some polished surface like mirrors etc. it can be avoided by:
- Changing to matt finish.
- Changing the task position or its surrounding.
- Using a light source of low brightness.
- Arranging the geometry of the installation so that no reflection at viewing direction.
- Providing supplementary lighting.
Avoidance of shadow:
- Shadow affects the amount of illumination and is caused by fixing light sources too wide apart or in the wrong positions so that light is obstructed by some object.
- Shadow on the surface, the near door for entry or exit, near tool rack, or on the job table is not desirable. It must be removed by providing extra or local light, shifting the light source or the object causing a shadow.
- Deep shadows should be avoided.
- The human eye can clearly perceive differences in luminance of over 50%. It takes time to adopt sudden variation in the intensity of lighting from higher to lower.
- The distribution of light requires two problems to be solved:
- Uniformity of illumination.
- Elimination of shadows.
- Uniform distribution of lighting is desirable for most workrooms.
- The ability to see detail depends upon the contrast between the detail and its background.
- The greater the contrast, the difference in luminance, the more readily the seeing task is performed.
- The eyes function most comfortably and efficiently when the luminance within the remainder of the environment is relatively uniform.
Appropriate color contrast:
- The eye sees an object by the light it reflects and distinguishes its details mainly by color contrast.
- In addition to luminance contrasts, color contrasts may be influenced by the choice of the color of light.
- The choice of the correct color of the light depends on the task to be performed and the requirements to be met by vision.
- It may be noted that there must not only be adequate illumination to see an object clearly but also the object must be visible in its surroundings.
- It must have moderate color contrast.
- It is the property of light that facilitates the perception of surface colors and depends on the spectral composition of the light. The red surface appears red only if the light falling on it contains red, but it will appear brown under the yellow of sodium street lighting.
- The maximum value of the color rendering index is 100 and at this value, there is no shift. For example, an incandescent tungsten filament lamp has a color rendering index of 100, fluorescent tubes between 55 to 95, mercury vapor lamps approximately 45, and low-pressure sodium vapor lamps less than 25.
Effect of colour on safety:
- What is more perceived? Colour or light? What the eyes see is colour and colour contrast, rather than light.
- Lighting and colour are complementary and their effects are interdependent. Therefore they are considered together.
- No lighting scheme can be fully effective unless supplemented by well-chosen and well maintained coloured surfaces.
Need of colours:
- Improve lighting conditions.
- Decorate the environment.
- Increase efficiency and productivity.
- Improve quality and workmanship and normal skill.
- Improve labor morale and interest in work.
- Reduce accidents and increase safety.
- Reduce rejections.
- Reduce absenteeism.
- Raise the standard of good housekeeping.
- Improve building and machinery maintenance.
- Reduce hidden costs of the dull and gloomy atmosphere.
- Improve overall psychological and physiological effects on workers or better work performance.
Avoidance of flicker:
All lamps working on alternating current give lights which pulsates at twice the supply frequency. This type of discontinuous light of almost all frequencies can produce an effect like fleshing rapidly to show moving object stationary, in which a rotating or reciprocating object can appear to be stationary, or moving slowly, or even appear to be rotating in opposite direction, etc. this false belief can cause accidents in the industrial situation. It is a real hazard in the presence of moving machinery.
Natural Lighting of Factory Building:
- For industrial structures, daylight is obtained by roof glazing as windows are not much useful in lighting interiors of large halls.
- The interiors of the roofs are painted white to avoid glare. Different types of roofing commonly used in industries are:
- North Light Roofing.
- Double Pitched Roofing.
- Monitor Roofing.
North Light Roofing:
- In this type of roofing, glazing is arranged in the north direction only and is provided on the shorter and steeper sides as shown in the figure. Angles on the sides towards the north are generally kept from 25 to 30 degrees. A larger number of small north lights per span is preferred over fewer lights having the same total glazed area, so as to have more uniform lighting.
- This type of roofing is also known as a ‘saw toothed’ roof. Glasses are so fixed that they make an angle of about 25 degrees with the vertical at the bottom and of about 90 degrees at the saw tooth.
Double Pitched Roof:
- These are used where the span is more than those of north light roofing and hence these are nearly 10 to 15 % economical than that of north light roofing. For getting more illumination and uniform distribution, skylights on the sloping sides may be provided. To avoid glare, the interiors of the roofs are painted white.
In the monitor, roofing glazing is arranged in opposite vertical strips. This type of roofing is least efficient and gives only about half of the light of north light roofing. Hence, these are used where less intensity of illumination is required. In the packing and distribution halls; ware-house; chemical plant etc., monitor type of roof lights supplemented with the windows and artificial lighting is provided.