The main goal of industrial lighting is to facilitate the performance of visual tasks through high-quality illumination. Factors that affect quality illumination include contrast, luminance ratios, uniformity, distribution, shadows and glare.

Contrast
To be readily visible, each detail of a visual task must differ in luminance or color from its background. Visibility is at a maximum when contrast of an object with its background is very high. For example, black lettering on a white background exhibits high contrast and is very easy to read. However, yellow lettering on a white background is considered low or poor contrast and is very difficult to decipher. Whenever possible, task contrast should be made as high as possible. Higher illuminance through supplemental lighting may help compensate for poor contrast.

Luminance Ratios
Luminance, measured in candelas per square meter, is defined as light emitted from a surface and is often called brightness. In order for the eyes to function comfortably and efficiently, the luminances within the surrounding environment should be relatively uniform. Workers frequently relax by glancing away from a task, and they should not be forced to encounter extreme differences in luminance from those of the task. If a person's eyes are constantly adjusting to broad differences in lighting levels, the result is eye strain, fatigue and productivity loss. Also, accidents may be caused by the delayed eye adaptation when moving from bright areas to dark ones and vice versa. Therefore, all luminances in the field of view should be carefully controlled.and should not exceed the ratios below. In order to achieve the recommended ratios, luminaire distribution and fixture spacing need to be carefully evaluated.

*Luminance ratio control is not practical
+Classifications are:
A-Interior areas where reflectances of entire space can be controlled in line with recommendations for optimum seeing conditions
B-Areas where reflectances of immediate work area con be controlled, but control of remote surround is limited
C-Areas (indoor and outdoor) where it is completely impractical to control reflectances and difficult to alter environmental conditions

Uniformity
According to the IESNA, uniform illuminance is achieved when "the maximum level is not more than one-sixth above the average level; or the minimum one-sixth below." This is appropriate when similar industrial tasks requiring the same amount of light are closely spaced. It is potentially a waste of energy to maintain uniformity between adjacent areas that have significantly different visibility and illumination requirements such as storage racks next to an inspection area. In these instances, the designer will need to apply the appropriate illumination to each area, taking care not to exceed the recommended maximum luminance ratios. To accomplish this, use luminaires of different wattages, change the quantity and spacing of luminaires in those areas or use task lighting.

Spacing Criteria
In order to maintain good uniformity in a space, the manufacturer’s published spacing criterion (SC) for a given fixture must be known. If you multiply the spacing criterion by the distance from the bottom of the fixture to the workplane, you arrive at the maximum recommended fixture spacing. Fixtures with low SC have more of a downward throw and need to be spaced closer together to maintain uniformity, and fixtures with higher SC have a more widespread distribution and can be spaced further apart. Spacing criteria are based on providing uniform illumination and are not a means of defining illuminance levels.

Distribution
The illuminance on the vertical plane is a critical element in most industrial environments. Many tasks such as machining processes, control panels, assemblies, levers, gauges, shelving and stacks are located in the vertical plane. Also, large machinery may obstruct the light and cause shadows unless good lighting techniques are applied. To light the vertical plane, pay close attention to fixture selection and fixture placement. Fixtures with wide distributions may be required in addition to supplemental task lighting to appropriately light the vertical plane and overcome obstructions.

Shadows
Harsh shadows in an industrial environment are not desirable and can be avoided by providing illumination from many different fixtures or from large diffusing luminaires. However, soft shadows that are less pronounced can accent the depth and form of objects. Clearly defined shadows often aid in the visibility of engraved polished surfaces, some types of benchwork and certain textile inspections. Supplementary directional lighting combined with diffused general lighting from several fixtures can help achieve this effect.

Glare
Glare is defined by the IESNA as "…the sensation produced by luminance within the visual field that is sufficiently greater than that to which the eyes are adapted." Glare can cause fatigue, headaches, annoyance, discomfort and productivity loss due to reduced visual performance and visibility. There are two types of glare, direct glare and reflected glare. Direct glare is caused by high luminance directly in the field of view. Reflected glare, also known as veiling reflections, results when luminance from an overhead fixture reflects on a shiny surface and reduces visibility and contrast.

To reduce direct glare:

To reduce reflected glare