8/14/97 AC 43-204
• Replace clear lamps with diffuse-coated ones.
B D FIGURE 3-4. EXAMPLES OF DIRECT AND REFLECTED GLARE (Courtesy of General Electric Company)
• Change the lighting system, if required. For example, replace HID downlight luminaires with those that have large-area lenses (large surfaces will be less bright and reduce reflections) or with fluorescent.
• Use a large-area fluorescent lighting system.
reflections will be uniform and low in luminance.
A translucent panel system is often recommended for inspecting mirrored metal and plastic articles for surface defects.
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• Use specialized supplementary lighting where the glare problem is limited to a few locations.
g. Luminaire Shielding. The purpose of a luminaire is to control or direct the light from the lamp. This is accomplished by the size, shape, and material of the reflector and auxiliary devices such as baffles, louvers, lenses, and diffusers.
For industrial lighting applications, including inspection areas, shielding should be at least 25 degrees and preferably approaching 45 degrees (see Figure 3-5), especially in areas of high illumination levels or with high-brightness lamps. Fluorescent fixtures might also require crosswise baffles or louvers if inspection personnel view the lamps lengthwise. At low mounting heights, well-shielded, narrow-beam luminaires, particularly HID, may produce puddles of light at the viewing task level. If wider beamspread and better uniformity is obtained by reducing shielding, the visible bare lamp becomes glaring. The following recommendations are provided for avoiding this problem:
Low Mounting Heights. Install HID luminaires that have been designed for low mounting heights. These have large diameter reflectors and refractors that provide the widespread beam. Because the light from the lamp is spread over the refractor's much larger areas, it in effect becomes the light source.
Therefore, the brightness is diluted and reduced to tolerable levels. Brightness will vary with the lamp's output and the size of the refractor.
Narrow-Beam Luminaires. Use more of the same narrow-beam luminaires, but with lower-wattage lamps and closer spacing. Properly selected, there will be both acceptable overlap and reduced direct glare. Fluorescent lamps, even though they are inherently lower in brightness than HID lamps, should have deep reflectors and lateral baffles.
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FIGURE 3-5. EXAMPLE OF LUMINAIRE SHIELDING ANGLE (Courtesy of General Electric Company)
h. Uniformity of Illumination. Uniformity refers to the variations in illumination levels that occur at the work plane, typically with the highest level under the luminaire and the lowest in between luminaires. The IES considers illuminance to be uniform if the maximum level is not more than one-sixth above the average level; or the minimum, one-sixth below. Uniform horizontal illumination is called for in most lighting designs where seeing tasks require the same levels. Closer spaced luminaires improve uniformity and ensure continued illumination in the event one or two luminaires are temporarily extinguished. Using IES recommended reflectances (see Table 3-5) helps improve uniformity and helps reduce unwanted shadows. Ceilings should be painted a flat white to reduce contrast between fixture and ceiling and to increase illumination. The key to satisfactory uniform lighting is to observe the fixture manufacturer's recommended maximum spacing-to-mounting-height ratio or a similar guide, the spacing criterion.
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TABLE 3-5. RECOMMENDED REFLECTANCE VALUES FOR INDUSTRIAL
LIGHTING SURFACES REFLECTANCE* (Percent) Ceiling 80 to 90 Walls 40 to 60 Desk and bench tops, machines 25 to 45 and equipment Floors not less than 20 Reflectance should be maintained as near as practical to recommended values.
(1) Maintaining Uniformity. Maintaining uniformity of illumination between adjacent areas which have significantly different visibility and illumination requirements might be wasteful of energy; for example, a storage area adjacent to a machine shop. In such instances, it is prudent to design and apply nonuniform lighting between those areas. It may be accomplished by using luminaires of different wattage and/or by adjusting the number of luminaires per unit area. Local lighting restricted to a small work area is unsatisfactory unless there is sufficient general illumination.
(2) Harsh Shadows. Harsh shadows should be avoided, but some shadow effect may be desirable to accentuate the depth and form of objects. There are a few specific visual tasks where clearly defined shadows improve visibility and such effects should be provided by supplementary lighting equipment arranged for the particular task. Figures 3-6 and 3-7 illustrate how shadows can aid or hinder the seeing of details. In the case of curved and faceted surfaces which are polished or semipolished, the direction of the lighting is important in controlling highlights. Some shadow contributes to the identification of form.
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FIGURE 3-6. HARSH SHADOWS PRODUCED BY UNIDIRECTIONAL ILLUMINATION (Left) AND SOFT SHADOWS PRODUCED
BY DIFFUSE ILLUMINATION Chap 3 Par 301 Page 79
FIGURE 3-7. MULTIPLE SHADOWS (Upper Left) ARE CONFUSING;
SINGLE SHADOWS (Center) MAY CONFUSE, BUT CAN HELP; DIFFUSED LIGHT (Lower Right) ERASES THE Brightness. Brightness is the strength of sensation which results from viewing surfaces or spaces from which light comes to the eye. This sensation is determined in part by luminance (which can be measured) and in part by conditions of observation, such as the state of adaptation of the eye. The eye responds to differences in brightness or contrast. Improving the contrast of the seeing task is the goal of the lighting designer.
However, extreme variations in brightness in the surrounding field of view can make seeing more difficult or even uncomfort- The eye becomes tired when the pupil has to adjust constantly from light to dark and back again. As recommended by the IES, the ratio of the luminance of the seeing task to the surrounding areas for comfortable seeing is shown in Table 3-6.
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TABLE 3-6. RECOMMENDED MAXIMUM LUMINANCE RATIOS FOR
INDUSTRIAL LIGHTING Environmental Classification* B
1. Between tasks and ad- 3 to 1 3 to 1 5 to 1 jacent darker surroundings
2. Between tasks and ad- 1 to 3 1 to 3 1 to 5 jacent lighter surroundings
3. Between tasks and more 10 to 1 20 to 1 remote, darker surfaces 4 • Between tasks and more 1 to 10 1 to 20 + remote, lighter surfaces
5. Between luminaires 20 to 1 (windows, skylights, etc.)
and surfaces adjacent to them
6. Anywhere within normal 40 to 1 + field of view * Classifications are:
A Interior areas where reflectances of entire space can be controlled in line with recommendations for optimum seeing conditions.
Areas where reflectances of immediate work area can be controlled, but control of remote surroundings is limited.
Areas (indoor and outdoor) where it is completely impractical to control reflectances and difficult to alter environmental conditions.
Luminance ratio control not practical.
i. Color. Accurate color identification is required for many visual inspection tasks of aircraft and related articles (color-coded electronic wiring and tubing, paint, penetrant and nagnetic particle inspection indications, corrosion, sarety signs, etc.). The inspectors' reaction to various colors and how they feel about the area can also be important. Most characteristics of a light source can be analyzed objectively; however, color and color-rendering properties are much more subjective.
Additional information on color is provided by the IES in its handbooks on lighting.
(1) Chromaticity. Chromaticity or color temperature (whiteness) of a light source sets the tone of the space: warm (yellow, pink) or cool (blue, green). It is measured in Kelvins (K). The warmer the appearance, the lower the number; the higher the number, the bluer or cooler the color. Figure 3-8 shows the approximate color temperatures in Kelvins of several electric light sources and daylight.
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- 20000 Blue northwest sky
- 15000 Blue sky with thin white clouds Blue sky
- 10000
- 9000 7500K - 8000- high CRI fluorescents Average north sky
- 7000 - Uniform overcast sky Short-arc xenon - 6000 5000K Average noon sun high CRI fluorescents 5000 Average mixture of sun and skylight
CW & CWX fluorescent lamps
• 4000 Deluxe white mercury Warm deluxe mercury
WW & WWX fluorescent lamps 3000 - 100-watt incandescent lamp 25 watt incandescent lamp High-pressure sodium 2000 Candle flame FIGURE 3-8. CORRELATED COLOR TEMPERATURE IN KELVINS OF
SEVERAL ELECTRIC LIGHT AND DAYLIGHT SOURCES
(2) Color-Rendering. Another important quality of a light source is its ability to render the color of objects in a natural or familiar way. This is usually expressed in terms of a color-rendering index, or how well a lamp compares with a reference source of the same color temperature. The higher the number, the more nearly like the reference source. Fluorescent lamps are available in a wide range of color temperatures and color-rendering capabilities. When good color-rendering is extremely critical for inspection operations, daylight-simulating lamps are recommended. High-intensity discharge lamps trade-off, Chap 3 Page 82 Par 301
color-rendering for high efficiency and render colors in the good to poor range, however, metal halide lamps are the preferred HID source where color-rendering is important. Additional information on light source color-rendering is provided by the IES in its handbooks on lighting and in technical literature available from manufacturers of light sources.
(3) Illuminance Levels. The lighting recommendations in formance rather than for safety alone; therefore, they are not to be interpreted as requirements for regulatory minimum illuminance levels.
j. Types of Lighting Equipment. The manner in which light is controlled by the lighting equipment governs to a large extent the important effects of glare, shadows, distribution, and diffusion. Luminaires are classified in accordance with the way in which they control the light. Figure 3-9 gives the standard International Commission on Illumination (CIE) classifications for interior lighting equipment.
0-10% 10-40% 40-60% 90-100% 60-90% 40-60%
DIRECT SEMI-DIRECT GENERAL DIFFUSE 40-60% 60-90% 90-100% 40-60% 10-40% 0-10%
DIRECT-INDIRECT SEMI-INDIRECT INDIRECT FIGURE 3-9. INTERNATIONAL COMMISSION ON ILLUMINATION LUMINAIRE
CLASSIFICATIONS FOR GENERAL LIGHTING Lighting Applications. Most aircraft maintenance lighting applications call for either direct or semi-direct types of illumination. Industrial luminaires for fluorescent, highintensity discharge and incandescent filament lamps are available with upward light components which contribute to visual comfort by balance of luminances between luminaires and their back- Chap 3 Par 301 Page 83
AO 43-204 8/14/97 grounds. Figure 3-10 shows some typical lamp and fixture light distribution curves. Luminaires also require adequate shielding for visual comfort (see Figure 3-5). The shielding angle is particularly important for higher luminance sources. Good environmental luminance relationships can also often be achieved with totally direct lighting if the illuminances and room surface reflectances are high.
LAMP AND FIXTURE TYPE
HID HID FLUORESCENT HID
CANDLEPOWER DISTRIBUTION
SPACING-TO-MOUNTING-HEIGHT RATIO
0.7 1.0 1.3 1.9 FIGURE 3-10. TYPICAL LAMP AND FIXTURE LIGHT DISTRIBUTION CURVES (Courtesy of General Electric Company) Luminaires with upward components of light are preferred for most areas because an illuminated ceiling or upper structure reduces luminance ratios between luminaires and the background. The upward light reduces the dungeon effect of totally direct lighting and creates a more comfortable and more cheerful environment shown in Figure 3-11. It shows the importance of a white ceiling in an industrial facility under construction. Note the improved visual environment in the right bay (where the painters have finished the ceiling) compared with that in the left bay (as yet, unpainted). The illuminance in the right bay is also substantially higher.
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FIGURE 3-11. ILLUSTRATION OF THE IMPORTANCE OF A WHITE CEILING
FOR IMPROVING THE VISUAL ENVIRONMENT OF AN INDUSTRIAL
FACILITY (Courtesy of General Electric Company) Luminaire Top Openings. Top openings in luminaires generally minimize dirt collection on the reflector and lamp by allowing an air draft path to move dirt particles upward through the luminaire to the outer air. Therefore, ventilatec types of luminaires have proven their ability to minimize maintenance of iluorescent, high-intensity discharge, and incandescent filament types of luminaires. Gasketed dust-tight luminaires are also effective in preventing dirt collection on reflector and lamp surfaces.
(3) High Humidity or Corrosive Atmosphere and Classified (Hazardous) Location Lighting. The National Fire Protection Association (NFPA) is phasing out the word "Hazardous" for the word "Classified."
Nonclassified Areas. Enclosed gasketed luminaires are used in nonclassified areas where atmospheres contain nonflammable dusts and vapors or excessive Enclosures protect the interior of the luminaire from conditions prevailing in the area.
Severe corrosive conditions necessitate knowledge of the atmospheric content to permit selection of proper material for the luminaire.
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AC 43 - 204 8/14/97
• Classified Areas. Classified locations are areas where atmospheres contain inflammable dusts, vapors, or gases in explosive concentrations.
are grouped by the National Electrical code on the basis of their hazardous characteristics, and all electrical equipment should be approved for use in specific classes and groups. Luminaires are available, specifically designed to operate in these areas, which are noted in Article 500 of the National Electrical Code as Class I, Class II, and Class III locations. Luminaires used in these areas are designated as: explosion-proof, dusttight, dust-proof, and enclosed and gasketed.
Other Factors. In selecting industrial lighting equipment, the following other factors lead to more comfortable Lighting installations:
• Light-colored finishes on the outside of luminaires to reduce luminance ratios between the outside of the luminaire and the inner reflecting surface and light source.
• Higher mounting heights to raise luminaires out of the normal field of view.
• Better shielding of the light source by deeper reflectors, cross baffles, or louvers. This is particularly important with high-wattage incandescent filament or high-intensity discharge sources and the higher output fluorescent lamps.
• Selecting light control material, such as mirrored or nonmirrored aluminum, prismatic configured glass, or plastic that can limit the luminaire luminance in the shielded zone.
k. Supplementary Lighting. Difficult seeing tasks often require a specific amount or quality of lighting which cannot readily be obtained by general lighting methods. Supplementary luminaires are often used to solve such problems by providing higher illuminances for small or restricted areas. Supplementary luminaires are also used to furnish a certain luminance, color, or to permit special aiming or positioning of light sources to produce or avoid highlights or shadows to best portray the details of the task. Figure 3-12 shows examples of placement of supplementary luminaires.
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