Economics and lighting level recommendations

The Illuminating Engineering Society of North America develops light level recommendations for tasks where visual performance is important. The 1959 and 1972 recommendations for illumination levels were based on the principle of delivering a fixed level of performance as predicted by the visual performance models of the time. This same principle is being considered for future revisions to the recommendations. There is currently no explicit method for determining whether a given fixed performance level is in any sense optimal or best. Visual performance increases with lighting levels, but so do economic and environmental costs. These costs lessen the economic benefits of the improved visual performance. A formal method for including these factors in light level recommendations is to restate the problem in terms of net benefits (benefits minus costs). The resulting equations have well defined optima versus light level, and thus give an explicit estimate of what the best lighting levels are in terms of current visual performance models, and current economic conditions. A simple net-benefit procedure is described, and sample calculations are shown for two current visual performance models. Fixed performance levels do not provide economically optimal recommendations with either model. There are also differences between models, but they are less significant than the large differences between the principles of fixed performance levels and economic optimization.