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Blue crest between the wavelength of 460 nm and 480 nm was reported to present melatonin suppression effects, whereas effects of red light on circadian rhythm regulation remain unclear. Spectrum plays an important role in circadian rhythm regulation, yet a lot of researches focused on the correlated color temperature, although a correlated color temperature value corresponds to various possible spectrums. Here, we performed human factor experiments with 3 lamps on 17 participants, comprising 9 males and 8 females. Our results showed that spectrums with high blue intensity tended to cause abnormal regulations of melatonin and cortisol, while the abnormalities were likely to be compensated by the 606-635-nm red light, which was indispensable for the photo-biological effects concerning circadian rhythm regulation. Abnormal circadian rhythm regulation was also found to be influenced by the illuminance, as abnormalities were significant in 500 lux whereas they were likely to disappear in 250 lux, implying the existence of threshold doses to trigger abnormities concerning circadian rhythm regulation. Furthermore, circadian rhythm responses were distinct between males and females. Our work may have implications for the development of light source, as we suggest that lighting source designers should increase the 606-635-nm intensity for bed room luminaires to decrease melatonin suppression effects.

Human eye is a special kind of optical system, and its imaging quality and fatigue level seem susceptible to the illumination. In this study we were sought to develop a novel method to quantify ocular fatigue more accurately, and to assess the influence of light environment on ocular fatigue. Human factor experiments were performed on a total of 1249 participants. Among all physiological parameters, only accommodation and the 12th aberration presented significant variations during visual tasks. We deducted the ocular fatigue equation based on these two parameters together with other structural data. Regression equation and neural network were also constructed as complements. As a test, we predicted the ocular fatigue accumulations in various visual tasks. It was implied the predicted fatigue accumulations fell in separate ranges. It seems the novel method developed in this study could predict ocular fatigue accurately, and provide guidance to luminaire design.

Light-emitting Diode (LED) has been considered as one of the new generation lighting sources with several merits such as high efficiency, high reliability, long lifespan, high-speed response, and energy saving. The optical performances of an LED luminaire, such as illuminance, luminance, correlated color temperature, and spectra power distribution, determine the lighting environment which can affect the human ocular physiological characteristics. To investigate the effect of optical performances on human vision, previous studies have assessed the subjective perception based on questionnaires. In this paper, we propose a novel method based on the aberrations and accommodations data from 150 human factor measurements on a total of 25 participants. The results show that: 1) optical performances of the LED luminaire have an influence on ocular physiological characteristics during the visual task duration, which can be quantized by the variations of physiological parameters; 2) the desk illuminance and light distribution curve are selected in this study as the optical parameters. The variations of ocular physiological characteristics reach the minimum values when the desk illuminance is 550 lux and the light distribution curve is large beam angle; and 3) ocular physiological characteristics are more sensitive to the light spatial distribution compared to the light quality. Thus, the proposed assessment method based on variations of ocular physiological characteristics in this paper is promising as one of the guidelines for the design and optimization of the LED luminaires.

The illuminance index has been widely used in the field of photometry, although the luminance contains more information on not only light intensity but also light direction. In this study, we clarify which photometric index is more competent to describe the influence of lighting environment on human eye. In this study, we propose a novel methodology to investigate the photo-biological effect of the lighting environment by human factor experiment. With the human factor experiments performed on 20 participants, we compare the variations of ocular responses during the Landolt-rings-counting visual task in lighting environments with similar illuminance while distinct luminance changes. With the same Correlated Color Temperature (CCT) and Spectral Power Distribution (SPD), optical performances with similar illuminance values present quite different influences on ocular responses, and the response variations are found to vary with luminance values. It is implied that the regularity of luminance influence on the ocular responses to lighting environment is likely to be dependent on luminance value instead of illuminance, and the photometric index luminance seems more appropriate to be used to assess the lighting quality in standards.

Correlated color temperature (CCT) is an important feature of the LED luminaire. However, its influence on visual discomfort remains vague due to the lack of a comprehensive study based on ocular physiological parameters and psychological assessment. In this paper, the investigation was carried out by the measurement of ocular parameters and the collection of subjective score. Three physiological parameters were used including higher order aberrations, modulation transfer function, and the ratio of accommodative convergence to accommodation ratio. It is shown that CCT has significance influence on human eye, and the proper CCT for the ocular health of moderate myopia people is near 5000 K. In addition, the results imply that the perception of discomfort is caused by psychological perception rather than ocular fatigue.