Spectral Power Distribution Variations May Have Implications for Myopia Research

Regardless of variations in spectral power distribution (SPD) values with respect to location, time, day and season, the spectral power of ambient light is significantly higher in outdoor locations compared with indoor locations, according to research published in Ophthalmic and Physiological Optics. These findings may be instrumental in explaining correlations between spectral power and myopia and have implications for myopia research, the report suggests. 

Researchers explored variations in the spectral composition of ambient light by recording SPD (wavelength range, 380–780 nanometers) using a handheld spectrometer at 3 outdoor locations (an open playground, under a shaded tee, and under a canopy) and at 3 indoor locations (a room with multiple windows, a closed room, and a closed corridor). The team recorded measurements 5 times per day (3-hour intervals) on 2 days each in the summer (March-June) and monsoon (July-October) seasons.

Overall, the median SPD value across the 3 outdoor locations (0.11; interquartile range [IQR], 0.09-0.12 W/nm/m²) was 157 times higher compared with the indoor locations (0.0007; IQR, 0.0001-0.001 W/nm/m²). The researchers observed substantial locational, diurnal and seasonal variations in the distribution of the median SPD. The highest outdoor SPD value captured was in the open playground setting (0.27; IQR, 0.21-0.28 W/nm/m²) followed by the shaded tree (0.083; IQR, 0.074-0.09 W/nm/m²), and canopy (0.014; IQR, 0.012-0.015 W/nm/m² ). The room with multiple windows registered a SPD value of 0.023 W/nm/m².  

In both the outdoor and indoor locations, the relative percentage composition of short (380-500 nm), middle (505-565 nm), and long (625-780 nm) wavelengths were comparable, and the proportion of middle wavelengths was significantly higher (P <.01) compared with the short and long wavelengths in all the locations, except for the canopy, according to the report.

“[W]e observed that the overall SPD of ambient light, and the spectral power of short, middle and long wavelength light vary with location, time, day and season. Irrespective of such variation, SPD outdoors was always higher than that of indoor locations,” according to the researchers. “If the spectral composition of ambient light has any role in influencing refractive status, then careful recommendations related to myopia management need to be developed accordingly.”

Study limitations include failure to explore the association between SPD and myopia and failure to explore the influence of digital devices on children’s retinal illumination.