A first approach to a new index on indoor lighting comfort based on corneal illuminance

In this study, the conditions of visual comfort were assessed in an indoor environment intended for students. For this reason, a transversal field survey was carried out in two libraries, one at the Sapienza University of Rome (Italy) and another at the University of Granada (Spain). During the analysis, measurement of lighting engineering variables such as horizontal illuminance, corneal illuminance, and luminance was carried out at the same time. The randomly selected individuals were asked to compile the structured questionnaires voluntarily at both sites. The first part of the questionnaire covered personal information, such as gender, age, eye color, etc. While the latter part evaluated the perception and visual preference of interviewees. In particular, we analyzed the visual perception on the basis of a five-point scale (-2÷+2), where positive and negative values identified visual comfort and discomfort, respectively. Each point was related to both related measured values of the lighting project variables and values of the personal data derived from the questionnaires. The subsequent statistical analysis (carried out through parameters and methodologies such as evaluation of the Variance Inflation Factor, Multicollinearity and Best Subsets Analysis) allowed the development of a new empirical index that is easy to apply, i.e., the Predictive Visual Comfort Index (PVCI). Some of the independent variables included horizontal illuminance, corneal illuminance, and age. In the design phase, once the other variables had been set, it was useful to determine the necessity of corneal illuminance to ensure visual comfort. The influence of each variable on the index and visual comfort was also quantified.