Attempt to Predict Utilization Factors on Working Plane within Shadow under Task Ambient Lighting

Abstract

The number of luminaires in an office in the field of lighting design is usually determined with the lumen method, which uses utilization factors. These factors are calculated by luminous flux incident on the working plane to that irradiated from the light source, assuming a non-obstructed room. Lighting design techniques with the lumen method are very useful if they are applied to an office with fixtures and task ambient lighting, which is a combination of local-lighting and general-lighting systems. We applied lighting design to a working plane within shadow under task ambient lighting, and paid attention to utilization factors with the lumen method. That is, we evaluated the correction coefficients where the utilization factors in setting up fixtures and a shadow caster (i.e., a globe the size of a human head) could easily be predicted by multiplying the utilization factors for a non-obstructed office and the correction coefficients. The utilization factors using the lumen method on the working plane within shadow for ambient light sources and a task light source were first examined based on results derived from illuminance calculations using the Monte Carlo method that treats notion of the luminous flux as a set of numerous particles. The validity of correction coefficients used to calculate utilization factors within shadow under task ambient lighting was then evaluated. As a result, utilization factors within shadow can be predicted by simply multiplying them by the correction coefficients in non-obstructed rooms with ambient light sources or from direct components without a shadow caster for a task light source.