Document O3Gk28djNpn8oQZ8wM56dRk5w

INDUSTRIAL BUILDINGS AND PLANT LAYOUT Types of lighting Natural lighting. Daylight is an ideal type of illumination However, light from overhead diagonal windows causes less glare than that from outside windows only When practicable, existing sawtooth, monitor, or skylight windows can be fitted with re fracting, diffusing, or tinted glass to re duce intensity and thus alter the character istics and improve the distribution of day light, particularly from distant parts of the room. For most effective use of daylight, a defi nite floor/window area relationship must be maintained * A single-story industrial build ing should have a window area equal to not less than 30 per cent of the floor area Reflection of daylight from surfaces out side the building should be utilized Light colors should be used for extenors of struc tures, walls of courts, and roofs of saw tooth buildmgs For best reflection, these surfaces must be kept bnght Windows, too, must be kept clean Sudden transitions from bnghtly lighted to dim areas--and vice versa--are danger ous the result is momentary blindness due to the lag in eye accommodation. Grada tions of light between areas of different in tensities will remedy this difficulty Vene tian blinds, shades, or drapes can be used to balance daylight and reduce glare Artificial lighting has become so accepted as an element of modern life that its origi nal supplementary character has been large ly forgotten. Artificial lighting has become die major source of illumination because natural light is undependable, especially in the winter when work schedules do not co incide with daylight. For continuous shift operation artificial light is essential. For other types of opera tion, it must be relied upon from 20 to 50 per cent of the total working hours, exclud ing overtime work or night work. Ceneral lighting is the base or minimum amount of light required It has been de fined as uniform distribution of light to pro duce equivalent seeing conditions through out an interior This is the type most commonly used for large general offices, schoolrooms, factories, and similar interiors. Localized general lighting sources usual ly are arranged 10 ft or more above the work to prevent too great a contrast m brightness between the more highly lighted work area and the adjacent areas and to provide sufficient light for general safety and for ordinary visual needs Light intensity on a surface vanes in versely with the square of the distance be tween the surface and the source of the light A source 10 ft above a surface would give four tunes more light to the work area than would the same source 20 ft high. Where visual needs are more critical, there fore, additional lighting can be provided by fixtures placed fairly close to the area need ing more light Standards Lighting requirements for industrial op erations vary considerably A table of mini mum standards of illumination for indus trial interiors as recommended by the Il luminating Engineering Society is given in Chapter 45, "Safety Engineering Tables " A convenient device for measuring illu mination is a light meter. This gives a direct reading of the number of footcandles of light reaching the work surface. Lighting requirements are determined by a visibility meter, which gives a direct reading of the number of footcandles re quired to see the task being studied as com pared to a selected standard task. The rela tive ease of seeing objects that vary in shape, size, and detail can be evaluated The direction of light and the degree of diffu sion required for maximum visibility also can be determined Glare Care must be taken throughout the light ing system to avoid glare Glare has been described as "any brightness within the field of vision of such diameter as to cause dis comfort, annoyance, interference with vi sion, or eye fatigue " It may be direct or reflected Direct glare causes visual discomfort be cause the sensitivity of the eye is disturbed, whereas reflected glare interferes with visi- 0Illuminating Engineering Society, 1860 Broadway, New York City. Dayhghting, Lighting Handbook oalbld Clare and Lighting Design 14-14