IES TM-24-13

This Technical Memorandum (TM) addresses how the Spectral Power Distribution (SPD) of light sources can be incorporated into the IES Illuminance Determination System for visual tasks that are categorized as P through Y within interior lighting applications. The summary of research investigations included in this TM describes how light spectrum affects pupil size, visual acuity, and visual efficiency under the conditions of interior lighting conditions, and concludes that light source SPD can be factored into lighting calculations for interior lighting applications under limited conditions when visual tasks require the ability to discern visual detail to ensure speed and/or accuracy in the performance of the visual task. These tasks are defined in this TM as visually demanding tasks and are a subset of visual tasks within IES Category P through Y of the Illuminance Determination System. This TM introduces the Equivalent Visual Efficiency (EVE) calculation and provides general guidelines and relevant caveats for its use. The calculation is optional and its use should be balanced with other lighting design criteria and objectives.