Background: Artificial light sources such as Light-emitting Diode (LED) emit more intensive blue light (460 to 490 nm) and are with a wavelength distribution deviating from the peak wavelength of 550 nm in natural sun light. The present study examined how cold and warm LED lamps with high- and low-blue light emission differently affected objective ocular responses and subjective viewing symptoms. Methods: 34 adults with normal or correct-to-normal vision read printed continuous text with one of three lamps (LED 4000 K, LED 6500 K and OLED 4000 K) generating 50 and 110 Nits for 60 mins respectively while their pupil size, accommodative response (increase of refractive power or the shortening of focal distance) and vergence angle (the degree of eyes turning inward) were continuously recorded at 50 Hz. Before and after reading their viewing symptoms were also surveyed, as well as overall discomfort at every 10-min interval. Results: with a lower luminance of 50 Nits, LED 4000 resulted in greater vision-related symptoms (blurry, double vision, eye pain) than OLED 4000 and LED 6500; this was accompanied by smaller pupil, larger accommodative lag, and larger vergence lag. With higher luminance of 110 Nits, LED 6500 and 4000 resulted in greater cognitive and fatigue symptoms, but not visual symptoms, compared to OLED 4000. Conclusions: LED at a lower illumination level causes insufficient focal distance and eye alignment and consequent blurred and double vision, as well as eye discomfort. The expected physical and cognitive fatigue associated with blue light emerges at a higher luminance. OLED is a better light source because it emulates normal light. As a result, it is more comfortable for sustained near work and allows better visual efficiency.
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