Fire Protection Research Foundation report: "Parameters for Indirect Viewing of Visual Signals Used in Emergency Notification" (PDF, 2 MB)
Authors: John D. Bullough, Nicholas P. Skinner, Yiting Zhu – Lighting Research Center, Rensselaer Polytechnic Institute
Date of issue: September 2013
A review of research performed for the Fire Protection Research Foundation by the RPI Lighting Research Center suggested that effective intensity may not be predictive of visual detection of signal lights when these are viewed indirectly or in the far-peripheral field of view. In particular, observers see the change in illuminance on room surfaces rather than the flashing light itself when it is not in the central field of view. Based on previous literature, the previous Foundation study suggested that a flashing light should increase the illuminance on the opposite wall by at least 7% in order for this increase to be detected reliably. For an ambient horizontal illumination level of 100 footcandles (fc) on the work plane in a space such as an office, it was estimated that the vertical illuminance on the wall should increase by at least 2 fc to be reliably detected. The objective of this project was to conduct a human factors laboratory study to identify whether the 7% increase in light level can be reliably detected by observers with normal vision when viewed indirectly.