Ambient Light Intensity in a Metropolitan Area: As a Prediction of Functional Pupil Size

1. Teresa Lau^1,2,3
2. Alvin Young^1,2,3
3. Lulu Cheng^1,2,3
4. Clement Tham^1,2,3
5. Dennis Lam^1,2,3

¹Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China
²New Territories East Cluster Ophthalmology Service, Hong Kong, China
³Prince of Wales & Alice Ho Miu Ling Nethersole Hospitals, Hong Kong, China

Purpose: To compare the ambient light intensities measured in urban and suburban areas in Hong Kong

Methods: Light intensity was measured using the Tenmars Lux/Fc light meter in 3 urban and 3 suburban areas in Hong Kong. Measurements were taken at 0 metres (m), 50m, 100m and 200m from the centre of the train station, in the directions of north, east, south and west of the station at 9pm local time. Results were statistically compared and analyzed.

Results: The ambient light intensities measured in urban and suburban areas were 228 +/- 56.3 lux (ranged 118 to 347 lux) and 73 +/- 26.9 lux (ranged 51 to 175 lux) respectively. Light intensity measured in suburban districts is lower than that of urban areas at all distances (0m, 50m, 100m, 200m) from the centre of the area, results were statistically significant (p<=0.05).

Conclusions: Subjective patient satisfaction with visual function after LASIK may be dependent on the illumination conditions of his or her living environment. It would be useful to be able to predict pupil size under different illumination conditions. If the mean ambient illumination in one's living environment is known, a more precise calculation of the treatment zone size may be tailored for each individual patient before refractive surgery.