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Nat Sci Sleep. 2017 Mar 8;9:59-65. doi: 10.2147/NSS.S123319. eCollection 2017.

Smartphone viewing distance and sleep: an experimental study utilizing motion capture technology.

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Department of Ophthalmology, Keio University School of Medicine, Tokyo.
Department of Ophthalmology, Keio University School of Medicine, Tokyo; RIKEN Center for Advanced Photonics, Wako, Saitama; Department of Nursing, Aino University Junior College.
RIKEN Center for Advanced Photonics, Wako, Saitama.
Department of Neuropsychiatry, Keio University School of Medicine, Tokyo, Japan.
Department of Neuropsychiatry, Keio University School of Medicine, Tokyo, Japan; Department of Psychiatry, Hofstra Northwell School of Medicine, NY, USA.


There are studies reporting the negative impact of smartphone utilization on sleep. It is considered that reduction of melatonin secretion under the blue light exposure from smart-phone displays is one of the causes. The viewing distance may cause sleep disturbance, because the viewing distance determines the screen illuminance and/or asthenopia. However, to date, there has been no study closely investigating the impact of viewing distance on sleep; therefore, we sought to determine the relationship between smartphone viewing distance and subjective sleep status. Twenty-three nursing students (mean age ± standard deviation of 19.7±3.1 years) participated in the study. Subjective sleep status was assessed using the Pittsburgh Sleep Quality Index, morningness-eveningness questionnaire, and the Epworth sleepiness scale. We used the distance between the head and the hand while holding a smartphone to measure the viewing distance while using smartphones in sitting and lying positions. The distance was calculated using the three-dimensional coordinates obtained by a noncontact motion-sensing device. The viewing distance of smartphones in the sitting position ranged from 13.3 to 32.9 cm among participants. In the lying position, it ranged from 9.9 to 21.3cm. The viewing distance was longer in the sitting position than in the lying position (mean ± standard deviation: 20.3±4.7 vs 16.4±2.7, respectively, P<0.01). We found that the short viewing distance in the lying position had a positive correlation to a poorer sleep state (R2=0.27, P<0.05), lower sleep efficiency (R2=0.35, P<0.05), and longer sleep latency (R2=0.38, P<0.05). Moreover, smartphone viewing distances in lying position correlated negatively with subjective sleep status. Therefore, when recommending ideal smartphone use in lying position, one should take into account the viewing distances.


blue light; distance; sleep; smartphone

Conflict of interest statement

Disclosure Taishiro Kishimoto has received consultant fees from Dainippon Sumitomo, Novartis, and Otsuka and has received speaker’s honoraria from Banyu, Eli Lilly, Dainippon Sumitomo, Janssen, Novartis, Otsuka, and Pfizer, outside the submitted work. He has also received grant support from the Pfizer Health Research, Takeda, Tanabe-Mitsubishi, Dainippon-Sumitomo, Otsuka, and Mochida, outside the submitted work. Masaru Mimura has received grants and/or speaker’s honoraria from Abbvie, Asahi Kasei, Astellas, Chugai, Cracie, Daiichi Sankyo, Dainippon-Sumitomo, Eisai, Eli Lilly, Fuji Film, Janssen, Meiji Pharma, Mochida, MSD, Novartis, Ono, Otsuka, Pfizer, Shionogi, Takeda, and Yoshitomi Pharmaceutical within the past 3 years, outside the submitted work. Kazuo Tsubota has received grants from Jins Co., Ltd, Toshiba Materials, and Tsubota Lav, outside the submitted work; in addition, he has a patent Tsubota Lab., Inc., pending and a patent Jins Co., Ltd., pending. The authors report no other conflicts of interest in this work.

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