Learning objectives
At the end of this lecture student will be able to : 1-Describe the requirements of good lighting . 2-Discuss suggestions for improving daylight illumination . 3-Define the terms noise and noise pollution . 4-Determine important properties for noise . 5-Specify basic instruments used in noise studies . 6-Identify effects of noise exposure . 7-Arrange control measures for noise . To a level accepted to the accreditation standard of the College .Light
The requirements of good lighting :- *Good lighting is essential for efficient vision. *If lighting conditions are not ideal, the visual apparatus is put to strain which may lead to general fatigue and loss of efficiency. *For efficient vision, the following light factors are essential:-1.Sufficiency In order to enable the eye to discern the details of the object as well as the surroundings without strain , an illumination of (15-20) foot candles is accepted as basic minimum for satisfactory vision. However it is variable between (5-100) foot candles according to the site and job.
2.Distribution Distribution of light should be uniform , having the same intensity , cover the whole field of work. If there are contrast differences in light ,it will strain the eyes and affect adversely the visual acuity. Proper dispersal of light ,without the production of shadows is necessary.
3.Absence of glare Glare is excessive contrast. e.g. automobile headlights at night. Direct glare from a light source. Glare Reflected glare from sources such as table tops and polished furniture. Glare causes annoyance .Eye cannot tolerate glare because it causes acute discomfort and reduces critical vision.
4.Absence of sharp shadows Slight shadows are inevitable ,but sharp and contrasting shadows are disturbing. Shadows cause confusion to the eye and therefore should not be present in the field of vision. 5.Steadiness The source of light should be constant. Flickering causes eye strain and may lead to accidents.
6.Colour of light Color of light is not very important so long as the intensity is adequate.Since natural light has a soothing effect on the eye, the artificial light should as far as possible approximate to the daylight color. 7.SurroundingsFor efficient vision ,color schemes in rooms are important.Ceilings and roofs should have a reflection factor of (80%) ,walls 50 – 60% , furniture 30-40% , reflection from floor not more than 15-20%.
Suggestions for improving daylight illumination:
The following general principles are taken into consideration in planning for best utilization of daylight. 1.Orientation *The brightness of the sky is not constant on the east and west, therefore illumination is variable in buildings facing east or west.*Direct penetration of sunlight may heat up rooms especially during summer. *Buildings are therefore oriented ,whenever possible, towards north or south for uniform illumination . This is particularly important in respect of schools, factories and laboratories where uniform lighting is required in all of the rooms.
2.Removal of obstructions Removal of obstructive buildings wholly or partially is likely to give the most effective single improvement in lighting. 3.Windows Windows should be properly planned ,the size, shape and arrangement of windows opening. *Tall window gives greater penetration of light. *Broad window gives greater diffusion of light.
*The rule that window area should not be less than 10% of floor area is now outdated. *Windows area is correlated to the purpose the room is intended to serve. *Usefulness of windows is reduced by covering them unnecessarily with curtains and screens.
4.Interior of the rooms. *The ceiling should be white ,the upper portions of the wall is slightly darker and lower portions some what darker leads to comfortable contrast. Noise:- *Noise is often defined as unwanted sound, but this definition is subjective because of the fact that ones sound may be another ones noise.
*A better definition of noise is “ wrong sound ,in the wrong place , at the wrong time” *Man is living in an increasingly noisy environment.*The 20th century has been described as the “century of noise“.*Noise has become a very important “stress factor” in the environment of man.*The term “ noise pollution “ has been recently coined to signify the vast cacophony of sounds that are being produced in modern life ,leading to health hazards.
*Sources of noise are many and varied (automobiles, factories ,industries , air-craft …etc). *Noise levels are particularly acute near railway junctions , traffic roundabouts ,bus terminuses and air-ports.*Domestic noises because of radio and TV.
*Two important properties for noise:
1.Loudness or intensity .It depend on the amplitude of vibrations which initiated the noise .It is measured in decibels (db).*Human ear responds in a non- uniform way to different sound – pressure levels i.e. it responds not to the level or loudness of a sound but to the perceived intensity.2.Frequency Frequency is denoted as Hertz (Hz).One Hz = one wave per second.*Human ear can hear frequencies (20 - 20000)Hz ,but this range is reduced with age and other subjective factors .>20 Infra –audible.<20000 Ultra –sonic.*Many animals (e.g. dogs ) can hear inaudible sounds.
*Sometimes noise is expressed in psycho – acoustic terms- the phone.Phone is a psycho-acoustic index of loudness. It takes in consideration intensity and frequency.*Basic Instruments used in studies on noise are :-1.Sound Level Meter . dB.2.Octave Band Frequency Analyzer Octave bands.3.Audiometer Measures the hearing ability.
Effects of noise exposure
I. Health Effects II. Economic Effects
A/Auditory effects. 1.Auditory fatigue .(at 90 dB and 4000 Hz) 2.Deafness Temporary Permanent (Up to 24 hours) ( 4000 -6000 Hz) *The victim is generally un-aware of it in early stages.*Repeated or continuous exposure to noise around 100 dB may result in a permanent hearing loss*Inner ear damage may vary from minor changes in the hair cell endings to complete destruction of Organs of Corti. *When this occurs as a result of occupation it is called “occupational hearing loss”*Exposure to noise <160 dB may rupture the tympanic membrane and cause permanent loss of hearing.
B/Non –auditory effects1.Interfernce with speech communication (300-500 Hz) . Such frequency present in noise of road and air traffic. 2.Annoyance .It is a psychological response.Neurotic people are more sensitive to noise than balanced people.3.Effeciency *Mental concentration is to be undertaken.*A low level of noise is always desired.*Reduction in noise has been found to increase work output.
4.Physiological Changes. A number of temporary physiological changes occur in human body as a direct result of noise exposure:- a-Rise in blood pressure. b-Rise in intracranial pressure. c-Increase heart rate. d-Increase breathing rate. e-Increase sweating. f-Several symptoms such as giddiness, nausea and fatigue.
g-Interference with sleep. h-Visual disturbances (narrowing of pupil which affect color perception and reduce night vision).
II. Economic losses. The potential cost of noise induced hearing loss to industry is quite great.