See Art. 15.20, Bibliography. As indicated in Art. 15.11, quantity and quality of light are actually inseparable in contributing to good lighting, although they are treated separately, for convenience of presentation, in this section. Illumination should meet the requirements of visual tasks for safe, efficient performance, esthetic reasons, and the purpose of attracting attention. Factors that affect visual performance of a task include: Luminance, or brightness, of the task Luminance relation between task and surroundings Color rendering of the light Size of details to be detected Contrast of the details with their background Duration and frequency of occurrence of the task Speed and accuracy required in performance of the task Age of workers The influence of these factors on visibility is described in Art. 15.10. Dim lighting is sometimes desirable for mood effects. For merchandising, however, a pattern of brightness is depended on to capture the attention of potential customers. For task lighting, sufficient lighting must be provided on the work area if the task is to be executed without eyestrain and fatigue. Higher than the minimum required level of illumination usually improves visibility but often with greater energy consumption and increased life-cycle costs for both lighting and cooling the TABLE 15.5 Weighting Factors for Determining

11.47.4 Stainless-Steel and Bronze Windows These are high-quality materials used for durability, appearance, corrosion resistance, and minimum maintenance. Stainless steel is rustproof and extremely tough, with great strength in proportion to weight. Weather stripping of stainless steel is quite often used for wood and aluminum sash. Bronze windows are durable and decorative and used for many fine commercial and monumental buildings. 11.47.5 Weather Stripping and Storm Sash Weather stripping is a barrier against air leakage through cracks around sash. Made of metal or a compressible resilient material, it is very effective in reducing heat loss. Storm sash might be considered an overall transparent blanket that shields the window unit and reduces heat loss. Weather stripping and storm sash also reduce condensation and soot and dirt infiltration, in addition to decreasing the amount of cold air near the floor. Storm sash and screens are often incorporated in a single unit. FIGURE 11.33 Wind-load chart indicates maximum glass area for various nominal thicknesses of plate, float, or sheet glass supported on four sides to withstand specified wind pressures, with design factor of 2.5. Article 4.31 describes various types of glass available for use in windows. Thickness. Figure 11.33 can be used as a guide to estimate thickness of plate, float, or sheet glass for a given glass area, or the maximum area for a given thickness to withstand a specified wind pressure. Based on minimum thickness permitted by Federal Specification DD-G-451c, the wind-load chart provides a safety factor of 2.5. It is intended for rectangular lights with four edges glazed in a stiff, weathertight

* Current criteria typically requires higher levels of ventilation air. Lights may be assumed to average 4 W/ ft2. Assume 50 persons will be in the store, 2 in the first-floor office, 10 in the second-floor office No. 1, and 5 in secondfloor office No. 2. Cooling Measured in Tons. Once we obtain the cooling load in Btu per hour, we convert the load to tons of refrigeration by Eq. (13.15). Cooling Requirements for First-Floor Store (Table 13.15a). Load in tons 7.25 tons If supply air is provided at 18
F differential, with fresh air entering the unit through an outside duct, the dehumidified air flow required for sensible heat is [from Eq. (13.30)]: TABLE 13.15b First-Floor Office Load Btu/hr Heat gain through enclosures: North wall, 102  0.25  15 382 North glass, 18  1.04  15 281 Partition, 30  0.39  10 117 Floor, 79  0.25  10 198 2 occupants (sensible load) at 255 510 Lights, 79  4  3.42 1080 Fan hp 4% 103 Total internal sensible load 2671 Fresh air (sensible load) at 2 changes per hour, 32  1.08  15 518 Total sensible load 3189 Occupants (latent load), 2 at 255 510 Fresh air (latent load), 32  0.67(99
77) 473 Total latent load 983