Discomfort Glare Cut-Off Values From Field and Laboratory Studies

Abstract

For the application of discomfort glare metrics, a categorisation is used, dividing the metric scale into categories of perception. These categories are separated by borderline values, or so-called cut-off values. Recent literature shows that these cut-off values are lower when they are derived from field study data than those derived from laboratory study data. To investigate this further, the data from one field study and two laboratory studies was used to derive and compare cut-off values corresponding to three borderlines. The results show that the field study cut-off values were systematically lower than the laboratory study ones, implying that discomfort glare is reported at lower stimulus magnitudes in the field. Although further research is required on that topic, several hypotheses are discussed in order to explain the gap between cut-off values derived from field data and cut-off values derived from laboratory data. Recommendations for future studies are also provided.

Comparison of questionnaire items for discomfort glare studies in daylit spaces

“…The 25% threshold was used for gatekeeping criteria for weather stability used in the field. 53,54 For the second and third studies, we removed data points where the GHI deviated more than 25% (GHI max –GHI min )/(GHI mean ), as measured by an on-site outdoor pyranometer (every 1 second). We exceptionally accepted a few more data points where the E v or GHI deviation was higher than 25% during the typing task period but not during the survey response period.…”

Long-term visual quality evaluations correlate with climate-based daylighting metrics in tropical offices – A field study

“…7 It is based on vertical eye illuminance and contrast identified by luminance sources detected in the Evalglare program through different algorithms, as shown in a follow-up study. 56,57 The Unified Glare Rating (UGR) -shown in equation 2-is the preferred glare metric of the CIE, 58 and it is based entirely on contrast. In both equations, E is the vertical eye illuminance in lx, L s is the luminance of the glare source in cd/m 2 , !…”

“…In this study, contrast for both UGR and DGP annual calculations is based on a 2000 cd/m 2 threshold. 57 Categorical results scales for the DGP 60 and UGR 58 metrics are reported in Table 2 DGP…”

An examination of range effects when evaluating discomfort due to glare in Singaporean buildings

“…Figure 1 Data collected in the study by Jakubiec et al 16 Figure 1 shows that the range of daylit conditions in the test rooms used by Wienold and Christoffersen 3 may not be applicable to buildings in Singapore. In fact, Pierson et al 18 showed that test room settings generally produced higher vertical illuminances than field studies, which had collected measurements inside occupied buildings. The authors 18 concluded that stimulus range differences across different environments may have biased the ratings given by observers since in field studies with lower vertical illuminance levels, building occupants expressed discomfort at lower DGP thresholds than in test room studies.…”

“…In fact, Pierson et al 18 showed that test room settings generally produced higher vertical illuminances than field studies, which had collected measurements inside occupied buildings. The authors 18 concluded that stimulus range differences across different environments may have biased the ratings given by observers since in field studies with lower vertical illuminance levels, building occupants expressed discomfort at lower DGP thresholds than in test room studies. *Approximately the highest value of DGP for observers that reported glare.…”