Lighting calculation methods

Eley et al. (1993) describe the following lighting calculation methods:

The skilled application of computerized point lighting calculations can optimize lighting levels in both the task and ambient domains in order to minimize energy consumption. The lighting professional should consider the use of point lighting calculations, both to design more energy-efficient spaces, and to create spaces with more drama and visual interest.

Point calculations are an exceptionally accurate way to compare general lighting systems. While the easier lumen method allows the comparison of average illuminance, point calculations permit the comparison of uniformity of light on the work plane, the patterns of light produced on ceilings and walls, and task contrast rendering. More specifically, point calculations allow consideration of the effects listed below.

Cautions for Point Calculations. In the case where a task light is used, or where an indirect fixture is mounted within 12 inches of the ceiling, point calculations are not always appropriate. In general, if the luminaire is close to the surface where lighting patterns are to be evaluated, a near field situation exists. A shortcoming of the mathematics used in point calculations is that these near field calculations are comparatively inaccurate unless near field photometric data is available from the luminaire manufacturer, or the computer program is capable of adjusting the characteristics of the luminaires to improve the accuracy of the results. Otherwise, it may be more accurate to evaluate the light patterns from the task light or indirect fixture empirically.

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