TABLE 107.2 Illuminance Categories and Illuminance Values for Generic Typ ivities in Interiors Ranges of Illuminances Category Footcandles Reference work-plane with dark 20-30-50 2-3-5 rientation for short 50-75-100 5-75-10 General lighting pace 100-150-200 10-15-20 throughout spaces casionally performed Performance of visual tasks of high contrast 200-300-500 20.-30-50 r large size Performance of visual tasks of medium E 500-750-1,000 Illuminance on task contrast or small size Performance of visual tasks of low contrast 1,000-1,500-2,000 100-150-200 or very small size Performance of visual tasks of low contrast and very small size over a prolonged perio Performance of very prolonged and exacting 5000-7,500-10000500-750-1,000 nation of ger isual tasks Performance of very special visual tasks of 10000-15000-20,0001,000-1,500-2,000 lighting) Source: IES Lighting Handbook, Application Volume. To compensate for reduced visual acuity, more illuminance is needed. Using the average age of workers as the age criterion is a compromise between the need of the young and the older workers and, therefore, a valid criterion Task background affects the ability to see because it affects contrast, an important aspect of visibility. More illuminance is required to enhance the visibility of tasks with poor contrast. Reflectance is calculated by dividing the reflected value by the incident value. The data given in Tables 107.3 and 107. 4 are taken from the IES Lighting Handbook [1987] and are applied to provide a single value of illuminance from within the range Illuminating system design can begin after the desired value of illuminance for a given task has been determined. Based on the IES Handbook, the zonal cavity method of determining the number of luminaires and lamps to yield a specified maintained luminance remains unchanged. Illumination Computational Methods Zonal Cavity Method. Introduced in 1964, the zonal cavity method of performing lighting computations has gained rapid acceptance as the preferred way to calculate number and placement of luminaires required to tisfy a specified illuminance level requirement. Zonal cavity provides a higher degree of accuracy than does the old lumen method, because it gives individual consideration to factors that are glossed over empirically the lumen method Definition of Cavities. With the zonal cavity method, the room is considered to contain three vertical or cavities. Figure 107.1 defines the various cavities used in this method of computation. Height for luminaire to ceiling is designated as the ceiling cavity (ha). Distance from luminaire to the work plane is the room cavity (hr), and the floor cavity(hg)is measured from the work plane to the floor. for each of the three cavities. Following is the formula for determining the cavity rtig e"cavity ratio"(CR) To apply the zonal cavity method, it is necessary to determine a parameter known as th 5h(room length (107 (room length x room width) where hequals ha for ceiling cavity ratio(CCr),hn for room cavity ratio(rCr),h for floor cavity ratio(FCR) e 2000 by CRC Press LLC© 2000 by CRC Press LLC To compensate for reduced visual acuity, more illuminance is needed. Using the average age of workers as the age criterion is a compromise between the need of the young and the older workers and, therefore, a valid criterion. Task background affects the ability to see because it affects contrast, an important aspect of visibility. More illuminance is required to enhance the visibility of tasks with poor contrast. Reflectance is calculated by dividing the reflected value by the incident value. The data given in Tables 107.3 and 107.4 are taken from the IES Lighting Handbook [1987] and are applied to provide a single value of illuminance from within the range recommended. Illuminating system design can begin after the desired value of illuminance for a given task has been determined. Based on the IES Handbook, the zonal cavity method of determining the number of luminaires and lamps to yield a specified maintained luminance remains unchanged. Illumination Computational Methods Zonal Cavity Method. Introduced in 1964, the zonal cavity method of performing lighting computations has gained rapid acceptance as the preferred way to calculate number and placement of luminaires required to satisfy a specified illuminance level requirement. Zonal cavity provides a higher degree of accuracy than does the old lumen method, because it gives individual consideration to factors that are glossed over empirically in the lumen method. Definition of Cavities. With the zonal cavity method, the room is considered to contain three vertical zones or cavities. Figure 107.1 defines the various cavities used in this method of computation. Height for luminaire to ceiling is designated as the ceiling cavity (hcc). Distance from luminaire to the work plane is the room cavity (hrc), and the floor cavity (hfc) is measured from the work plane to the floor. To apply the zonal cavity method, it is necessary to determine a parameter known as the “cavity ratio” (CR) for each of the three cavities. Following is the formula for determining the cavity ratio: (107.1) where h equals hcc for ceiling cavity ratio (CCR), hrc for room cavity ratio (RCR), hfc for floor cavity ratio (FCR). TABLE 107.2 Illuminance Categories and Illuminance Values for Generic Types of Activities in Interiors Illuminance Ranges of Illuminances Type of Activity Category Lux Footcandles Reference Work-Plane Public spaces with dark surroundings A 20–30–50 2–3–5 Simple orientation for short temporary visits B 50–75–100 5–7.5–10 General lighting Working spaces where visual tasks are only throughout spaces occasionally performed C 100–150–200 10–15–20 Performance of visual tasks of high contrast or large size D 200–300–500 20–30–50 Performance of visual tasks of medium contrast or small size E 500–750–1,000 50–75–100 Illuminance on task Performance of visual tasks of low contrast or very small size F 1,000–1,500–2,000 100–150–200 Performance of visual tasks of low contrast and very small size over a prolonged period G 2,000–3,000–5,000 200–300–500 Illuminance on task, obtained by a combi￾nation of general and local (supplementary lighting) Performance of very prolonged and exacting visual tasks H 5,000–7,500–10,000 500–750–1,000 Performance of very special visual tasks of extremely low contrast and small size I 10,000–15,000–20,000 1,000–1,500–2,000 Source: IES Lighting Handbook, Application Volume. cavity ratio 5 (room length + room width) (room length room width) = ¥ h