Degree of eye opening: A new discomfort glare indicator

• A new objective indicator of glare was developed: degree of eye opening (DEO).
• DEO is sensitive to vertical illuminance at the eye (p = −0.503; s = 0.0001).
• DEO overcomes the limitations of glare prediction models.
• The proposed ocular indicator has a post occupational use and operates in a broad light range.

The degree of eye opening (DEO) is proposed as a new indicator of glare in sunny climates in the presence of direct sunlight. A laboratory experiment was carried out (n = 20) in a simulated office space where volunteers performed computer office tasks. Four lighting situations, based on ranges of vertical illuminance at the eye level were evaluated. By means of a visible spectrum eye-tracker DEO was registered in each scenario. The proposed indicator was obtained by mathematical iterations and showed a good correlation with: vertical illuminance at the eye (r = −0.503; α = 0.0001), Daylight Glare Probability (DGP) (r = −0.649; α = 0.0001) and Glare Sensation Vote (GSV) (r = −0.580; α = 0.0001). This new indicator operates in a broad range of lighting conditions, from a low vertical illuminance at the eye scenario with diffuse daylight to a very high vertical illuminance at the eye scenario with uncontrolled direct sunlight. The proposed new indicator satisfies the following criteria: high validity, reliability, diagnostic power and acceptability and it also addresses unresolved aspects of current glare predictive models: GSV, DGP and DGI.