LED illuminants: Effect of correlated color temperature on pupil size in off-axis vision

Abstract

The increased of LED technology is becoming more prevalent in our society due to its high energy efficiency. LEDs present different correlated color temperature (CCT); however, there is no evidence on how it influences pupil size. Previous studies have found variations in pupil size with retinal illumination for a single illuminant in the foveal area, where cones? density is high. Therefore, this pilot study has been conducted to analyze the influence on pupil size of the CCT, luminance and age at a retinal eccentricity of 10°. A pupilometer installed in a two-channel Maxwellian view optical system was used and four subjects, two young and two older, participated in this experiment. Pupil measurements were performed for six background luminances ranging from 0.01 to 50 cd/m2 provided by LEDs with different CCT: 2700, 4000 and 6500 K. As for the results obtained, we have observed that the pupil diameter decreases with increasing luminance and is larger for young than for old subjects for the same background luminance. Regarding CCT, in both young and old subjects, and for all background luminances, CCT does not influence pupil diameter.We can conclude that in off-axis vision the pupil size decreases with the luminance value in a similar way as it does in fovea. Old subjects have smaller pupil diameters than younger subjects for all luminances and for all illuminants, regardless of the CCT. Moreover, the decrease in pupil size at photopic luminance, where photoreceptors are saturated, is predictably caused by excitation of melanopsin cells.