Effect of correlated color temperature and illuminance on sustained attention collected via electroencephalography signals

This study aimed to explore the differences in the subjects' sustained attention under the impact of nine lighting conditions consisting of the combination of three commonly used correlated color temperature (CCT) (3300 K, 4300 K, and 5300 K) and illuminance levels (300 lx, 500 lx, and 750 lx) to provide guidance on the adjustment of CCT and illuminance level parameters for indoor lighting. We selected 24 physically and mentally healthy university students (12 male and 12 female) as the experimental subjects. The subjects were required to perform sustained attention to response task (SART) activities under the nine different lighting conditions and collected the alpha (α) waves (8–12 Hz) from the electroencephalography signals. Subsequently, the mean power spectral density of the α waves and various SART parameters were analyzed and tested. Finally, the effects of different CCT and illuminance levels on the subjects' attention were compared. With the increase in CCT, the attention level tended to increase linearly, whereas the attention level was the lowest at 300 lx and the highest at 500 lx and appeared as an inverted “U” shape. The subjects' attention level was the highest at the combination of CCT of 5300 K and illuminance level of 500 lx and the lowest at the combination of CCT of 3300 K and illuminance level of 500 lx. These results provide important data to elucidate the impact of lighting condition on attention.     

A common type of commercially available LED light source allows for colour discrimination performance at a level comparable to halogen lighting

Abstract

As light sources based on light emitting diodes (LED) are increasingly used to replace classic tungsten-based light sources in household lighting applications, possible impairments of colour perception under those light sources due to a different spectral power distribution become a major concern. The Colour Rendering Index (CRI) which is the only measure available to the end user is controversial and does not represent a comprehensive measure of colour perception. Aspects of colour perception disregarded by the CRI such as colour discrimination have to be taken into account as well. Therefore, we evaluated colour discrimination performance under a commercially available phosphor-converted LED light source from a popular brand (OSRAM) in comparison to a classic tungsten-based halogen light source. Colour discrimination performance was not affected by the type of light source, indicating that the phosphor-converted LED light source enables colour discrimination performance comparable to that of halogen lighting despite being associated with a lower CRI.

Practitioner summary: Considering the increasing use of energy efficient light sources, we compared colour discrimination under a common type of phosphor-converted LED and under traditional halogen lighting. Colour discrimination performance was comparable in both lighting conditions, indicating that the phosphor-converted LED can replace halogen lighting without sacrificing colour discrimination for energy efficiency.

Abbreviations: LED: light emitting diode; CRI: colour rendering index; CCT: correlated colour temperature; CIE: commission internationale de l’éclairage; FMHT: Farnsworth-Munsell 100-Hue Test; lm: lumen; lx: lux, lumen/m^2; W: watt; nm: nanometer; K: kelvin     

Neuro-controller for broadcast lighting light-emitting diode to express white light with high color rendering index

Technical characteristics analysis related to correlated color temperature (CCT), color rendering, and illuminance is required to use light-emitting diode (LED) as broadcast lighting. In general, to realize a white light source with a high color rendering index (CRI), we selected the appropriate emission intensity of RGBW LED through trial and error. However, the characteristics of the LED light source and environmental conditions make it difficult to perform the procedure several times. The objective of this study was to design a system that could control illuminance, CCT, and ∆uv while having high CRI, as an LED control method for broadcasting lighting. The controller implements using a feed-forward neural network with excellent nonlinear function approximation capability. We measure data directly from the red green blue white (RGBW) LED system for neural network training. We then select data with high CRI from the measured raw data and choose data for neural network learning by removing measurement noise using the quadratic polynomial interpolation method. The performance evaluation confirms that the proposed neural network controller shows excellent results as an RGBW LED controller for broadcast lighting in the Planckian locus and all regions of white light.     

Measuring the effects of lighting on the readability of electronic devices

The aim of this study was to understand to what extent people can read e‐paper devices under various conditions of ambient illuminance that can occur indoors. In this study, 110 young to elderly subjects participated in an experiment to evaluate the effects of 14 different levels of ambient lighting on their reading from three different electronic devises and paper text. The participants were asked to undergo a timed read task and then to evaluate the readability of two eReader devices (a regular electronic display and one with a front light) in comparison with a backlit liquid crystal device and conventional paper text. The results indicated that backlit and front lit devices are easier to read at less than 200 lx and the reflective device is easier to read at levels above 500 lx.     

Effects of text/background color combination,ambient illuminance,and display type on discriminating performance for young and elderly users

Abstract— This study examined the effects of text/background color combinations (black‐on‐white, red‐on‐white, green‐on‐white, and blue‐on‐white), ambient illuminance (50, 500, and 12,000 lx), and display type (color electronic‐paper displays and conventional transmissive liquid‐crystal displays) on the discriminating performance of young and elderly users. The results showed that when participants used the color e‐paper display, young participants had significantly better discriminating performance than elderly participants under the text/background color combinations of black‐on‐white, green‐on‐white, and blue‐on‐white, whereas no significant difference was present between young and elderly participants under red‐on‐white. When participants used a conventional transmissive LCD, however, there was no significant difference between young and elderly participants under all text/background color‐combination settings. Young participants had substantially better discriminating performance under 500 and 12,000 lx than under 50 lx, whereas elderly participants had the best discriminating performance under 12,000 lx, followed by that under 500 lx, and the worst performance under 50 lx. Participants who used a conventional transmissive LCD had substantially better discriminating performance under 500 and 12,000 lx than under 50 lx. Participants who used the color e‐paper display had the best discriminating performance under 12,000 lx, followed by that under 500 lx, and the worst performance under 50 lx. The results can be the guild for the designers of color e‐paper displays.     

Effects of ambient illuminance and electronic displays on users' visual performance for young and elderly users

Abstract— This study investigated the effects of age (young participants aged 20–30 and elderly participants older than 60), ambient illuminance (50, 500, 1 500, 3000, 6000, and 9000 lx) on participants' visual performance when using various electronic displays (conventional transmissive LCD, Ch‐LC display, and E‐ink display). Overall, the results indicated that participants' visual performance showed sign if icant difference among various ambient il luminance cond itions, electronic displays, and between two groups of participants. Significantly different visual performance was observed between young and elderly participants. The interaction among ambient illuminance, type of electronic display, and age had a significant effect on participants' visual performance. When participants used the E‐ink display, both young and elderly participants had significantly worse visual performance under an ambient illuminance of 50 lx compared to other illuminance settings. When participants used the Ch‐LC display, young participants had significantly worse visual performance under an ambient illuminance of 50 lx compared to other illuminance settings, but elderly participants had significantly better visual performance under an ambient illuminance higher than 1500 lx. When young participants used a conventional transmissive LCD, the ambient illuminance had no significant effect on their visual performance. When elderly participants use a conventional transmissive LCD, an illuminance of 50 and 6000 lx seem to have a detrimental effect on their visual performance.     

恒照度调光的LED驱动器设计

随着照明技术的不断发展以及能源的日益紧张,绿色照明成为主要的研究方向。本文针对传统照明能效低、耗电量大等问题,设计了LED恒照度调光驱动器。系统使用恒流LED控制芯片NCL30160作为LED光源驱动电路,采用TSL2561光照度传感器采集室内光照度,通过处理器相应算法进行闭环控制,实现室内的恒照度调光。该算法实现了PWM波形平滑变化,避免因PWM突变造成闪光。同时,系统增加了人体运动控制,实现无人、有人时的不同调光方案,使设计进一步节能和智能化。     

A complementary matching technique to reduce the variance of optical and electrical properties of light‐emitting diodes

Abstract— Light‐emitting diodes (LEDs) using phosphor conversion inherently have a wide variation of multiple parameters, including correlated color temperature (CCT), light output power (LOP), and forward voltage VF. A method, based on the formation of LED pairs with complementary characteristics, is presented to produce LED‐based light sources with narrow CCT, LOP, and VF distributions. A weighted matching algorithm was developed to select LED pairs under a multiple selection criteria. Based on the weighted matching algorithm, 96 LEDs were combined to form 48 LED pairs, and it was experimentally demonstrated that the variance of LED CCT and LOP distributions decreased by 93% and 71 %, respectively.     

Light for patient safety: Impact of light on reading errors of medication labels

BackgroundIn in-patient care facilities, 1 in 5 medication doses is administered incorrectly. A hospital environment which supports the performance of the health-care staff will positively impact patient safety.ObjectivesDetermine which lighting leads to the least reading mistakes of medication labels.DesignExperimental study with repeated measures.SettingStudy was performed under controlled conditions in the Netherlands.ParticipantsIn total the data of 37 participants are analyzed and described. Inclusion criteria were: female, aged between either 18–30 years old (M = 26.0, SD = 3.1) or between 55 and 67 years old (M = 57.9, SD = 2.7) years old, with normal vision. Eligible participants were personally invited to participate.MethodsPer participant, the readability of three different labels (Blister, Baxter and Orange) and four different font sizes (4.5 pt, 3.5 pt, 3.0 pt, and 2.5 pt Arial Capital) were assessed under nine different light conditions (three illuminances (E),100lx, 500lx, and 1000lx and three correlated color temperatures (T_cp): 3000 K, 4000 K, and 6500 K). The participants had to read out loud text sequences of 10 letters per medication label. The numbers of errors were counted and analyzed.ResultsThe results show a significant difference between numbers of errors related to: 1. Light condition, 2. Age, 3. Label material, 4. Font size. The impact of the light condition is not identical for the different types of label and the font sizes. The impact of the light conditions is the strongest for the smallest font size (2.5 pt) and participants with Visual Acuity < 1.ConclusionLighting has an impact on the number of errors. Older people make more errors than younger people. The type of label has an impact on the number of errors made. The font size has an impact on number of errors made. For font sizes <4.5 pt (Arial), reading medication labels (Blister, Baxter and Orange) under illuminance levels of 100lx, will lead to significantly more errors than E ≥ 500lx. The light condition that generates the least errors for the total test population, all font sizes, and all different materials was the one with an E of 1000lx and a T_cp of 4000 K. People with an insufficient Visual Acuity (VA) benefit most from a higher illuminance level, especially for the Orange labels. When the VA is well-adjusted (sufficient to good) and the font size is as recommended for medication labels (Arial Capital ≥ 4.5 pt) the impact of the lighting on number of errors is limited for all of the age groups.     

Physical‐based photon mapping for an LED backlight lighting simulator

Abstract— Liquid‐crystal displays (LCDs) have become increasingly popular due to their lower price and larger sizes. In particular, backlights having an RGB LED source have recently attracted attention, because they have a wider color gamut, higher luminance, and lower power consumption. However, even when the backlight area is uniformly covered with light modules based on arrays of individual LEDs, this does not ensure a uniform chromaticity and luminance over the backlight panel, thereby stressing the need for lighting simulation of the backlight. Accordingly, this paper proposes an effective lighting simulator to predict the chromaticity and luminance distribution of an LED backlight panel for an LCD. First, the spectrum‐based photons are all initially generated using a random function with a constraint satisfying the spectral power distribution of the actual LED light sources, while their emitting directions are determined based on a pre‐calculated probability using a random variable angle. The optical characteristics of the inner sheets in the LCD backlight structure are then modeled using the wavelength and incident angle to predict the next direction of each photon based on the reflection and transmittance at an intersection. All the photons that reach the unit area of the outward panel are gathered to shape their spectral power distribution, then converted to CIEXYZ values and multiplied with a color‐matching function. Finally, a realistic image visualization of these CIEXYZ values is achieved through standardized device characterization using the sRGB mode. Experiments confirm that the proposed spectrum‐based photon mapping can effectively predict the chromaticity and luminance distribution of an LED backlight panel, providing a good lighting simulation of an LED backlight before manufacturing the LCD.     

Effects of ambient illuminance on users' visual performance using various electronic displays

Abstract— This study investigated the effect of ambient illuminance (50, 500, 1500, 3000, 6000, and 9000 lx) on participants' visual performance using four electronic displays (conventional LCD under transmissive mode, conventional LCD under reflective mode, Ch‐LC display, and E‐ink display). Analysis results indicate that participants' visual performance shows significant difference under various ambient illuminance and electronic displays. The interaction between ambient illuminance and electronic display also has significant effect on participants' visual performance. When participants use the conventional LCD under transmissive mode, ambient luminance has no significant effect on participants' visual performance. However, participants' visual performance is significantly different under various ambient illuminances using the conventional LCD under reflective mode, Ch‐LC display, and E‐ink display. The conventional LCD under transmissive mode is the only choice at a lower illuminance of 50 lx. Higher illuminance (500 lx) for E‐ink displays may result in as good a performance as the conventional LCD under transmissive mode; nevertheless, much higher illuminance (1500 lx) for the conventional LCD under reflectance mode and Ch‐LC display may achieve better performance.     

Effects of color temperature and luminance of LEDs on color judgments involving various printing materials

This study investigated errors in color judgment related to stimuli (cyan vs. magenta vs. yellow) printed on various materials (coated paper vs. cotton vs. polyester fiber) and occurring in a range of visual environments (color temperature × luminance: 4000 K × 1500 lx vs. 4000 K × 750 lx vs. 2700 K × 1500 lx vs. 2700 K × 750 lx) under illuminated light‐emitting diodes. Participants included 16 female and 14 male Taiwanese college students [age range, 20–26 years (M = 21.92, SD = 2.13)]. Subjects were instructed to perform a series of comparative judgments in which they carefully observed a standard stimulus color under illuminated LEDs and judged which of five simultaneously presented colors under illuminant D65 was the most similar to the standard color. Data analysis revealed that the effect of visual environment on accuracy of color judgments against the standard was significant. Additionally, the accuracy of color judgments against the standard was significantly better for polyester printing material than it was for coated paper. The color of the standard also significantly affected color judgment accuracy: cyan yielded significantly worse accuracy rates than did magenta or yellow. These results have implications for lighting design and interior design.     

Investigation into the stability condition of correlated color temperature of white illumination sources based on trichromatic light-emitting diodes

We present a simple method to obtain a stable correlated color temperature (CCT) for the variation in light output power (LOP) of a light-emitting diode (LED) comprising a trichromatic LED-based white light source. A mathematical model was developed to determine the condition for the stable CCT operation using colorimetric analyses, and the stable CCT condition can be obtained by taking the derivative of the CCT with respect to the power ratio between the LEDs. Specifically, the stable CCT point that is invariant to the change in the LOP of a green LED can be uniquely determined at a certain value of the power ratio between red and blue LEDs. It was found that the chromaticity coordinate of the mixed white light moves along the isoCCT line of the Planckian locus as the LOP of a green LED varied under the stable CCT condition. The existence of the stable CCT point was also verified experimentally. The proposed method is expected to be advantageously employed in optimizing trichromatic LED-based white illumination sources for improved color stability.     

Lighting for road tunnels: The influence of CCT of light sources on reaction time

Drivers’ visual performance is closely related to traffic safety in a real driving environment. In order to improve the traffic safety of road tunnel lighting, the effect of LED lighting on human visual performance was investigated using reaction time as a parameter. The experiment was performed with a scale model that can simulate a road tunnel lighting environment. Reaction times were measured under different values of luminance, correlated colour temperature (CCT), eccentricity, and contrast. The results show that visual performance can be improved by increasing the CCT of the light sources. The improvement of visual performance is greater in peripheral vision than that in foveal vision. The shortest reaction times were measured at a luminance level of 10 cd/m² and at a CCT of 5000 K. An appropriate luminance value with high CCT is recommended for tunnel lighting in interior and transition zones.     

Assessment of visual fatigue under LED tunable white light with different blue components

Light‐emitting diode (LED) light source has high intensity emission of blue components absent in the daylight spectra and regulates human physiology and behavior. The aim of this study was to explore the effects of LED tunable white light with different blue‐component intensities on visual fatigue based on human eye photoreceptors. The short (S)‐cone and melanopsin illuminance were about 212% and 82% higher for blue‐enriched white light than blue‐less white light, respectively. The photopic illuminance was same for these two lights. The results revealed that blue‐enriched LED tunable white light with higher illuminance of S cones had a significant effect on visual fatigue. Participants experienced more eye discomfort under blue‐enriched white light accompanied with decreased vision function and changes in the autonomic nervous system. Visual acuity and tear film stability declined, and heart rhythm changed more significantly under blue‐enriched white light than blue‐less white light. While memory performance did not decline with more severe visual fatigue, improved memory performance under blue‐enriched white light may be due to enhanced alertness or arousal associated with high melanopsin illuminance. Our results suggest that blue‐enriched white light with higher illuminance of S cones and melanopsin has beneficial effects on cognitive performance, but it can induce relatively more visual fatigue.     

Effects of bending curvature and text/background color-combinations of e-paper on subjects’ visual performance and subjective preferences under various ambient illuminance conditions

The study used the simulated e-paper to investigate how the bending radius of curvature (−10 cm, plane, and 10 cm) and 12 text/background color-combinations of e-paper affect subjects’ visual performance and subjective preference under various ambient illuminance conditions (200 and 500 lx). Analysis results indicated that the bending curvature and ambient illuminance did not significantly affect subjects’ visual performance. However, subjects visual performance differed significantly for different text/background color combinations of the simulated e-paper. When the background color of the simulated e-paper was set to yellow-like condition and the luminance of the text was low (2.2 and 4.6 cd/m²), subjects’ visual performance was best. Regarding the subjective preferences of subjects, the results of this research also demonstrated that the bending curvature, text/background color combinations and ambient illuminance all significantly affected the subjective preferences of subjects. Subjects exhibited the best preference under the following settings: bending curvature of the simulated e-paper set to plane; background color of the simulated e-paper set to yellow-like condition and low text luminance (2.2 or 4.6 cd/m²); high ambient illuminance (500 lx).     

The effect of the illuminance of light emitting diode (LED) lamps on long-term memory

In this study, the effect of the illuminance of LED lamps on long term memory is verified in the conditions of 400 lx, 700 lx, 1000 lx according to the standards of study room illuminance between 400 lx, the minimum and 1000 lx, the maximum suggested by KSA 3011. Word fragment task is used to measure the long term memory. As a dependent task, 90 words made up of 7 letters are selected among 2700 words which have low frequency provided by sesame word. According to the experiment result, the rate of long term memory is 60.42% under the condition of 400 lx, which is the most effective, 59.38% under the condition of 700 lx, and 52.68% under 1000 lx. In addition, the p value between 400 lx and 1000 lx is 0.028, which is statistically significant. The significance of this study lies in that the effect of the illuminance of LED lamps on long term memory, rather than the existing issues such as attentiveness or work memory is searched, suggesting the possibility that the lower, rather than lighter the illuminance of LED light is, the more effective long term memory is.     

Dynamic color control in multiprimary tunable LED lighting systems

Temporally dynamic tunable light‐emitting diode (LED) lighting systems offer multiple spectral degrees of freedom and enable the creation of composite light spectra with a wide range of perceptual characteristics. Connecting existing metrics and ongoing research, this paper introduces relevant measures of quality of light, color, and temporal performance characteristics, including color rendition, circadian stimulation potential, and temporal smoothness and speed. Multiprimary system models describing both colorimetric and spectral characteristics are explained, along with colorimetric‐plus multiprimary intensity solutions that allow optimization of any of these quality of light characteristics in addition to ensuring a colorimetric match. Three commercial multiprimary LED systems are modeled to show examples of spectral solutions for different colorimetric‐plus optimization goals, and their range of performance are discussed. The diversity of results shows both the need for usable optimization tools and the need for clear communication standards about quality of light when light sources are capable of much more than typical fixed‐color lights.     

Conditions of emergency lighting

Emergency illumination must be provided in case of power failure in public buildings or places of work. A laboratory study of the mobility of subjects under simulated emergency illumination was performed to determine the level of emergency illumination necessary for a rapid exit, and to establish whether this level depends upon the normal illumination. Both young and elderly subjects were used. The experimental conditions were selected to simulate situations in which the occupants are not familiar with the escape route. In addition to measuring the time that the subjects needed to complete an escape, the subjects were asked to evaluate the lighting on several scales; and their ‘spare mental capacity’ during the escape was measured by their performance on a secondary mental task. The results showed that all measures of performance worsen as the emergency lighting is decreased below 2 Ix. The figure of 2 lx is appropriate for both normal light levels tested, 250 and 1000 lx. Where many elderly people are apt to be present, a minimum of 41x is advisable. These recommendations are higher than those prescribed by the British Standards (0-2 lx) and the Deutsche Industrie Norm (10 lx).     

A study on overhead glare in office lighting conditions

Abstract— High‐intensity light sources illuminating the human eye may create discomfort glare, or at higher intensities even disability glare. In many office lighting conditions, light from overhead luminaires in the ceiling may deliver stray light into human eyes, and as such create discomfort glare, generally referred to as overhead glare. In this paper, overhead glare for a LED luminaire comprising a matrix array of small LED sources using subjective evaluation methodologies and theoretical models, commonly accepted to evaluate glare, were investigated. The perceived overhead glare of the LED luminaire is evaluated at various luminance levels and at different angles (i.e., between 55 and 90°) with respect to the line of sight of the viewer. The results show that a luminaire comprising a matrix of high‐intensity point sources can cause overhead glare and can become glary at lower averaged luminance levels than a luminaire with a uniform light source even at high evaluation angles with respect to the line of sight of the viewer. In addition, the conventional UGR model for predicting discomfort glare needs adaptation for a reliable prediction of perceived overhead glare of complex LED luminaires consisting of a matrix of small‐sized high‐intensity light sources.