Abstract
Since the induction of the ESI system for evaluating interior lighting, there have been various metering methods developed for measuring actual lighting installations. Presently, ESI can be measured either directly or indirectly. Indirect-type measurements include such instruments as the visual task photometer and the visibility meter.2,3 Such meters determine an intermediate value such as contrast or CRF (Contrast Rendition Factor) from which ESI is calculated. Direct-type meters include ones such as the Holophane ESI meter4 and DiLaura's cylinders5 which fit over footcandle meter cells. In the first case a subjective comparison is needed for results and in the second, intermediate calculations are again required.
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