Correspondence | Published:

Response to Mahroo et al

Eye volume 27, page 991 (2013) | Download Citation



In response to the comment by Mahroo et al.1 on determining the accuracy of higher cut-off values of light meter readings to determine time spent outdoors vs indoors, we have evaluated the accuracy of cut-offs higher than 1000 Lux of 1200 and 1500 Lux.

The Intra Class correlation for the cut-off values of 1200 and 1500 Lux showed higher correlations between the light meter and diary recordings during the week in a school term and school holidays, compared with cut-offs of 800 and 1000 Lux (Table 1).

Table 1: Intra Class Correlation co-efficients (ICC) for cut-off values of 800, 1000, 1200, and 1500 Lux during the school term and school holidays

Thus, we agree with the proposal that the best cut-off value for evaluating outdoor vs indoor activities is 1500 Lux instead of 1000 Lux.


  1. 1.

    , , , , , . Potential effect of ‘cut-off intensity’ on correlation between light meter measurements and time outdoors. Eye 2013; 27(8): 990–991.

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Author information


  1. Department of Optometry/Ophthalmology, SRM Medical College Hospital and Research Centre, SRM University, TamilNadu, India

    • R Dharani
  2. Department of Biostatistics, Singapore Clinical Research Institute, Singapore

    • C-F Lee
  3. Center for Quantitative Medicine, Office of Clinical Sciences, Duke-NUSGraduate Medical School, Singapore

    • C-F Lee
  4. Saw Swee Hock School of Public Health, National University of Singapore, Singapore

    • E A Finkelstein
  5. Health Services Research Program, Duke-NUS Graduate Medical School, Singapore

    • S-M Saw


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Competing interests

The authors declare no conflict of interest.

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