Quantifying light exposure patterns in young adult students

Exposure to bright light appears to be protective against myopia in both animals (chicks, monkeys) and children, but quantitative data on human light exposure are limited. In this study, we report on a technique for quantifying light exposure using wearable sensors. Twenty-seven young adult subjects wore a light sensor continuously for two weeks during one of three seasons, and also completed questionnaires about their visual activities. Light data were analyzed with respect to refractive error and season, and the objective sensor data were compared with subjects’ estimates of time spent indoors and outdoors. Subjects’ estimates of time spent indoors and outdoors were in poor agreement with durations reported by the sensor data. The results of questionnaire-based studies of light exposure should thus be interpreted with caution. The role of light in refractive error development should be investigated using multiple methods such as sensors to complement questionnaires

Degree of correlation between total light interception and whole-canopy net CO 2

This paper shows the degree of precision by which measurement of total canopy light interception (TCLI) can estimate whole-canopy net CO2 exchange rate (NCER). The test vines comprised a single 35° NE-SW oriented hedgerow, with vertically shoot positioned grapevine canopies at either a low shoot density (10 shoots/metre of row) or a high shoot density (20 shoots/metre of row). TCLI was measured on different dates and at various times on each date (during the 2001 growing season) by a multiple line sensor equipped with 64 phototransistors (35 mm spacing). Each sensor had a spectral sensitivity in the 300-1100 nm waveband and the line of sensors was moved horizontally in steps of 10 cm. Whole-canopy NCER was recorded over successive clear days using an enclosure method. TCLI and canopy NCER were highly correlated on a seasonal basis for both the low shoot density treatment (R2 = 0.97) and the high shoot density treatment (R2 = 0.94). The correlation became less precise (R2 = 0.80 and 0.79 for low and high, respectively), when data taken at various times of day were treated separately. Canopy NCER derived from single TCLI readings taken at solar noon tended to be under-estimated, while NCER derived from single TCLI readings taken later in the afternoon tended to be over-estimated. Nevertheless, for a given training system, our method was sufficiently precise to predict seasonal increase of canopy NCER as well as the total leaf area at which NCER approached a maximum thus setting a value above which additional leaf area resulted in mutual shading without enhancing carbon assimilation