To construct a simple optical sensor for measurement of the sugar content in an aqueous solution, a bent optical fiber was used as the sensor. The attenuation ratio, i.e., the differences in the light intensity through the bent optical fiber when the sensitive part (bent part) was soaked in a reference material and sample solution, was closely related of the solute content in the samples. However, slightly difference in the light intensity were observed in the practical application because the sugar content in foods and other bio-systems was much lower than that in the tested samples. Therefore, we constructed a sensor system using a light emitting diode (LED), photo diode (PD) and simple electronic circuit as a differential amplifier. As a result, measurement of the sugar content ranging from 0 to 30 g/dm³ was successful and excellent agreement between the FT-IR method as the conventional method and the sensor method using an operational amplifier (OP-amp) was observed. In addition, the time courses of the sugar content and the uptake rate of plant cells were able to be calculated during the cultivation process. The process monitoring for the fermentation process management will be possible by using this sensor. These results suggested that the developed sensor using a bent optical fiber is applicable as a simple and disposable optical sensor.

White light emitting diode (LED) lighting is being used more frequently for illumination in recent years. The coupling of blue with yellow emitting phosphors produces white LED light. Blue light has a short wavelength in the visible light spectrum and exerts a strong influence on photobiological functions. Cycling light exposure is necessary for the synchronizing the circadian rhythm. The exposure to white light at subjective nighttime induces cognitive impairment, depression, and anxiety by disturbing the circadian rhythm and increasing stress hormone. However, few studies have been performed at the subjective daytime. Thus, the aim of this study was to determine whether exposure to blue light from an LED at subjective daytime affects brain function. We irradiated C57BL/6J mice with 200 lux of blue LED light for 12 h/day for 6 weeks at the subjective daytime and performed Y-maze, object recognition, tail suspension, and open field tests. There was no significant difference between the exposed mice and control mice. Histological analysis of the retina showed that the blue light exposure did not alter the retinal thickness. We conclude that the exposure to blue LED light at subjective daytime does not affect the retinal morphology or brain function in pigmented mice.

A laboratory based electroencephalography (EEG) study was conducted to investigate the probable temporal processes in the brain for detection of object designed under metal halide (MH) and high-pressure sodium (HPS) light sources. Participants in this study were instructed to respond to either match or mismatch condition in a match/mismatch-to-sample task. The image stimulus contained object under metal halide and high-pressure sodium lamp. The scalp topographic plots of the event related activity showed that object detection was faster under MH than HPS. Significant differences in scalp activity were also identified. This approach can be considered as future metric for assessment of lighting installation for visual acceptance designing.

With the advance of medium and high power light-emitting diodes (LED), tuneable light sources with sophisticated spectral power distributions have been emerging. The increasing variety of LEDs and their spectral behaviour complicates their design as well. Most notably, many different parameters have to be taken into account to describe the quality of light. This paper introduces a new characteristic, Spectral Deviation, which both combines various light quality parameters into one single value and correlates with the most commonly used quality parameters. Our Spectral Deviation allows a more time efficient quality assessment of a designed spectral power distribution without complex calculations or colour space transformations. The parameter is derived directly from the spectral power distribution of a test illuminant as the sum of absolute differences to a standardized reference distribution. A weighting function is used to take the characteristic of human perception into account. An upper limit for the parameter is proposed for the design of new spectral power distributions. Our parameter can be used during the selection process of single-emitter LED for tuneable luminaires as a preselector. It eliminates undesired solutions before even calculating detailed quality parameters, allowing more possible combinations to be checked in the same time.

We previously reported that light emitting diode (LED) light sources with longer wavelengths provided protans and deutans with greater red-green discrimination ability using a simulator and in volunteer subjects. Here, we focused on tritans, i.e., those with blue-yellow color blindness, and examined the effects of blue LEDs in a series of simulator studies. HRR pseudoisochromatic test plate No. 24 and SPP (standard pseudoisochromatic plates part 2) test plate No. 4 were illuminated by D65+LED (470 nm) or LED (470 nm)+LED (590 nm) and observed by a color vision simulator (chromatic vision simulator) that was produced on the basis of the Brettel’s theory. These results indicated that blue LED light sources were effective for color discrimination of tritans.

Light is the most important environmental signal for synchronizing human circadian rhythms. The circadian system is normally synchronized with the solar day, ensuring that the sleep–wake cycle and endocrine rhythms are timed appropriately. However, exposure to electrical lighting can also reset circadian rhythms. In this short review, we discuss properties of light stimuli that are important for resetting the human circadian system. The direction and magnitude of light resetting are circadian phase-dependent, with exposure to light in the early biological night resulting in a phase-delay shift of circadian rhythms, and exposure to light in the late biological night and early morning resulting in a phase-advance shift. Circadian resetting responses can be enhanced by increasing the irradiance or duration of the light stimulus, or by using short-wavelength blue light to activate intrinsically photosensitive retinal ganglion cells that express the photopigment melanopsin. This knowledge can potentially be applied to improve light therapy for circadian rhythm sleep disorders, and to help reset circadian rhythms in individuals exposed to shift work or jet lag.

In this paper, we present a high-power blue-violet (BV) indium gallium nitride (InGaN) laser diode (LD) and a high-brightness white light source using the InGaN LD. For realizing a high-power operation, we carry out two approaches. One is that the additional thick-optical-waveguide (TOW) is constructed on both sides of the active layer of the InGaN LD, which suppresses optical-loss and gives high wall plug efficiency (WPE). The other is that the LD chip on a submount is covered by another III-nitride ceramic submount, which reduces the thermal resistance. By using these novel optical-loss suppressing structure and double-heat-flow (DHF) packaging, the LD operates with a maximum output power of over 7.2 W at 25°C. In addition, a high luminous efficacy spot lighting system with a white light source using the InGaN LD is presented for lighting applications. By combining the high power InGaN LD, a phosphor and uniform illumination/high reflection optic elements, the system demonstrates the high light flux of 861 lumen and the high luminance efficacy of 51.3 lm/W.

Despite LEDs robustness against aging, it is known that silver-plated components in mid and low power LEDs suffers premature degradation when exposed to Sulfur- or Chlorine-compounds, even at low concentration. This issue can be particularly severe in LED luminaires, where also reflectors can be silver-coated. In this paper we describe a novel solution based on a getter powder able to effectively and irreversibly trap the noxious gases and prevent silver tarnishing.

The alternative current driven light emitting diode (AC-LED) lighting system has attracted a great deal of attention because of the high luminous efficiency and the simple electric circuit. However, this system causes the unacceptable flicker due to rapid fluctuations in the voltage of the power supply. In order to compensate the flicker effect in AC-LED, we proposed the use of yellow persistent luminescent garnet phosphors. The time evolution of luminescence intensity measurement of Ce³⁺ and Cr³⁺ co-doped Gd₃Al₂Ga₃O₁₂ phosphor using a modulated blue laser diode was performed. From this measurement, the flicker percent of Ce³⁺ and Cr³⁺ co-doped Gd₃Al₂Ga₃O₁₂ phosphor is calculated and showed to be about 60%. This result demonstrated that persistent phosphor is expected to solve the problem of flicker caused in AC-driven LED lighting system.

It is well-known that the presence of Volatile Organic Compounds (VOCs) within sealed LED bulbs can induce lumen output degradation during the device life. We studied the evolution of the luminous flux and of the gaseous contaminants on LED filament lamps purchased on the market: the increase of large organic molecules concentrations was observed after aging in some samples. As a matter of fact, the lamp with higher increase in larger molecules contamination showed also higher rate of luminous flux degradation.

Helium is currently used as main filling gas in sealed LED lamps. In the present study we show it exists a suitable gas alternative, based on hydrogen, with improved heat management properties. Moreover, a solid state dispenser-getter technology has been developed which allows high-purity dosing of the new thermal management gas in optimized and controlled quantities.

This paper details a novel method consisting of employing a pulsed-laser Raman scattering technique to estimate junction temperatures of several LED chips arranged in a straight line on a phosphor-less blue-LED package and a phosphor-resin coated blue-LED package. By using a sheet-shaped irradiation pattern, each of the GaN-E₂^H Raman spectra from several chips mounted straight on a phosphor-less blue LED package was observed at the same time and the junction temperature of each chip was estimated successfully by means of each Raman shift during operation despite the existence of strong LED emission. In addition, the GaN-E₂^H Raman signal from the phosphor-resin coated blue-LED was observed for the first time by using 633 nm laser to reduce the negative influence from the phosphor and light diffusing substances in the resin. It is concluded that this technique would be a useful method for a remote and standard system for 2D mapping of the junction temperatures of blue-LED packages.

A low pressure DC discharge formed from a mixture of one of the rare gases Ne, Ar, Kr or Xe plus water vapor is studied, water vapor being only a minor additive to a rare gas. Under some discharge conditions water molecules give hydroxyl molecules OH that produce very intensive UV emission 306.4 nm. It is shown that regarding all rare gases enhanced emission of the OH 306.4 nm band is registered from the discharge of Ar mixed with water vapor. The light production efficiency of the (Ar+H₂O)-plasma under study reaches 40–45 LPW that is about (40–45)% of a conventional mercury fluorescent lamp. The experimental data make it possible to propose several ways to increase the efficiency of a (rare gas+water vapour)-discharge plasma as a base for a light source: (1) addition of a second rare gas to the (Ar+H₂O)-mixture, (2) usage of TiO₂ catalyst to enhance the destruction of water molecules into hydroxyl and atomic hydrogen, and (3) pulse discharge operation which is usually known to give gain in efficiency. The obtained data concerning these ways present possible directions for further investigations and describe predictable results in case of their fulfilment.

The work is devoted to the effect of vacuum ultraviolet (VUV) radiation of excimer lamps (λ=172 nm) on the spores of various species of microscopic fungi. The dependences of the survival probability on the VUV radiation dose have been obtained. It was found that the survival probability depends on the spore’s phase of growth and cell wall pigmentation. The doses of spore inactivation in stationary phase were found to be higher as compared with the ones of exponential phase. The FTIR spectra indicate that the VUV radiation leads to degradation of proteins and polysaccharides. The atomic force microscopy indicates the possible photochemical nature of the spore inactivation. The inactivation of microfungi by VUV irradiation potentially can be caused by two mechanisms: cell wall damage and DNA destruction. The VUV doses of microfungi spores monolayer inactivation (λ=172 nm) were found to be lower in comparison with the ones of germicidal UV light sources (λ=254 nm).

To detect acoustic resonance (AR) in metal halide (MH) lamps, a simple high-sensitivity method with a multiplier detector is presented in this paper. Voltage envelope variations are measured to evaluate whether AR occurs in MH lamps. The study is focused on improving the sensitivity of an AR detection method. Several manufacturers’ MH lamps are tested in our experiment. In addition, the proposed method is compared to another voltage envelope detection method evaluating by a lock-in amplifier with high sensitivity and detection results are analyzed by statistical methods. The results show that the proposed circuit can provide similar sensitivity as the expensive lock-in amplifier to detect AR phenomena and the AR-free and the slight AR level can be easily distinguished.

In this work, modelling of emission spectra of neon and argon atoms in an inductive discharge is performed. The influence of generated into this discharge alternating electric field on spectral characteristics of light sources is studied. Based on the calculation results, the regularities in the behaviour of spectroscopic properties of Ne and Ar atoms in an alternating circularly polarized electric field have been revealed. Practical applications of the simulation results are considered.

Power line communication (PLC) signal attenuation in the intelligent control of light emitting diode (LED) road lamps is investigated. According to simulation results, a capacitive load in the LED power supply can cause more than 80% attenuation to high-frequency signals if the transmission distance is above 200 m. In this study, an inductor is connected in series with a capacitive load in the LED power supply to reduce the signal attenuation, so that the maximum transmission distance can be enhanced. The performance of the PLC-receiving node with the inductor is compared with that without the inductor. By measuring the switch-on signal voltage amplitude on the coupling coil of the power line carrier module, it is proved that the inductor, particularly at values of approximately 110 to 220 µH, can effectively reduce signal attenuation. Furthermore, the maximum transmission distance of PLC with the inductor can be enhanced in the lab environment.

In order to investigate the best lighting condition for chicken raising, 1440 Jinmao Broilers were divided into 10 groups with 10 kinds of monochromatic lighting conditions to compare the effects of different light colors on the growth performance, feather picking and comb size of broilers. Moreover, 210 Jinmao breeders were divided into 7 groups with long-wave band of visible light. The spectral irradiance of each group was adjusted to the same value. After several weeks, male broilers in 400–540 nm and female broilers in 540–660 nm grew faster than other groups. Breeders exposed to light of 740 nm had better performance in egg laying.

Phycocyanin (PC) is a kind of valuable pigment extracted from spirulina platensis (S. platensis). Light environment is one of the most important factors on the production of PC. Using light-emitting diode (LED) light sources, the S. platensis was cultured with five different ratios of red and blue photons. Photosynthetically Active Radiation (PAR) was precisely controlled by the function relationship between PAR, junction temperature and forward current. The comparative analysis shows that blue light is conducive to improve the mass fraction of PC, but the total production per incubator is lower than the one obtained under red light.

Based on the experimental visual data obtained for self-luminous stimuli surrounded by a dark background, a new colour appearance model (CAM) for unrelated self-luminous stimuli, CAM15u, was previously developed. To extend the model to related self-luminous stimuli, the colour appearance of coloured self-luminous stimuli surrounded by a luminous background was evaluated using the magnitude estimation method. Experiments have been performed in Belgium and in Argentina using two different experimental setups. With a LED setup in the Belgian laboratory, visual data on the perception of brightness, hue and amount of white of 30 coloured self-luminous stimuli surrounded by a luminous background were collected. Luminance levels of the stimuli and the background were respectively 50 cd/m² and 28 cd/m² (positive contrast condition). With a projector setup in the Argentinian laboratory, visual data on the perception of brightness and amount of white of 32 coloured self-luminous stimuli surrounded by a luminous background were collected. Luminance levels of the stimuli and the background were respectively 10 cd/m² and 5.6 cd/m² (positive contrast condition). For both experiments; the brightness scaling shows a clear and prominent Helmholtz–Kohlrausch effect. This effect describes the impact of the saturation of a stimulus on the perceived brightness and has been seriously underestimated in earlier CAMs. Both brightness, hue and amount of white are found to be well predicted by CAM15u, for this positive contrast condition.

Recently, products of light emitting diodes (LEDs) are expanding in many areas, such as lighting and display technology. As well as luminous flux measurement in the lighting technology, luminance measurement is also important in the display technology. In this study, a transfer standard for LED luminance measurement, which based on a high-power LEDs and a homogeneous optic, was investigated by means of ray tracing simulation to make direct traceable chain from calibration laboratory to manufacturer. The transfer standard was modeled with homogeneous optics such as microlens arrays or light pipe, and the optical properties of two-type models were analyzed with ray tracing simulation. The ray tracing simulation results showed that the luminance difference in the transfer standard with microlens arrays achieves ±4% within 5 mm in diameter and the angular distribution of it close to Lambertian surface. The other, the luminance difference in the transfer standard with a light pipe achieves ±5% within 5 mm in diameter. Two types of the transfer standard are not inferior in luminance uniformity and diffused property to common transfer standard such as a tungsten ribbon lamp in the ray tracing simulation results, and then it is worth examining as candidates of a transfer standard for disseminating of luminance scale.

Many manufacturers have been using either reflective or refractive optics in their LED luminaires to accomplish a specific lighting task. The advantages and sacrifices of both methods have not been fully investigated, since the investment needed to explore and research both technologies thoroughly are cost expensive. This paper intends to summarize the relative advantages of both technologies, based on experience with existing outdoor LED luminaire optical designs.

At present, the concept of intelligent lighting, such as LED dimming applications using PWM technology, is popular. However, it is acknowledged that the theories of photometry were developed fundamentally based on traditional light sources, so there is no existing research as to whether high-frequency pulsed light may cause any difference in these theories. In this paper we investigate the influence of pulsed light on vision and non-vision effects. Vision experiment comparing the brightness of DC light and pulsed light of different colors was conducted. Heart rate and blood pressure of subjects were also evaluated, when exposed to LED’s pulsed lights of different parameters. The experimental results show that pulsed light has different luminous efficiency from DC light, and longtime exposure to pulsed light influences human beings’ heart rate and blood pressure.

To investigate the effect of high-luminous-flux street luminaires on the visibility of vertical objects (i.e., oncoming pedestrians), feeling of discomfort glare, perception of scene brightness, sense of safety and security, and brightness uniformity, a target detection experiment and a subjective evaluation experiment were conducted under three lighting conditions in a real street. Veiling luminance calculations were also conducted by using a computer simulation. The results of the simulation showed that high-luminous-flux luminaires provided higher veiling luminances on targets than conventional luminaires. The results of the target detection experiment suggested that these veiling luminances impaired subjects’ target detections. In addition, the results of the subjective evaluations suggested that the street illuminated by the high-luminous-flux luminaires were perceived to be safer and more secured than that by conventional luminaires. Therefore, to improve the visibility of vertical objects and the perception of safety and security in nighttime streets, high-luminous-flux luminaires in streets should be used. However, cares are needed to maintain disability and discomfort glare as low as possible by shielding high-luminance luminous elements from pedestrians’ views.

To verify the validity of Stiles–Crawford’s formula that defines veiling luminance caused by a peripheral glare source on extra-foveal vision, this study conducted peripheral target detection experiments with/without a glare source located in the peripheral visual field. The experimental results suggested that veiling luminances obtained from our experiments was higher than that of the Stiles–Crawford formula. On the other hand, the exponents n of the regression curves obtained from our experiments were smaller than those of the Stiles–Crawford model. Thus, we attempted to modify the Stiles–Crawford formula based on our experimental data. It should be noted that veiling luminance caused by oncoming headlights may cause more serious disability glare to drivers in the real world than the Stiles–Crawford formula predicts.

Actual illumination values calculated in bad weathers may be significantly lower than theoretically calculated values. Therefore, it is necessary to investigate visibility under hazy conditions. In this study, a simulated fog environment is established for this purpose. It was observed that human visual acuity is strongly correlated with the level of fog density. The results obtained may contribute to the design of street lighting.

Bright nocturnal light has been known to suppress melatonin secretion. However, bright light exposure during daytime might reduce light-induced melatonin suppression (LIMS) at night. This study aims to evaluate the effect of high correlated color temperature LED light during daytime on LIMS. Male participants were exposed to different light conditions for 3 h in the morning (09:00–12:00). The light conditions were dim light (<10 lx), 125 lx high correlated color temperature (CCT) LED light, and 250 lx high CCT LED light. The subjects were then exposed to bright light (white light, 300 lx) for 1.5 h at night (01:00–02:30). Saliva samples were taken before (01:00) and after (02:30) exposure for evaluation of melatonin secretion. There were no significant differences in melatonin secretion before and after night-time light exposure on the 125 lx and 250 lx morning light conditions. Since these light intensities were almost equal to those in our previous study, the high CCT LED light might be appropriate for certain work places (e.g., hospitals and underground spaces), contributing to the reduction of our health risk and also saving energy.

It is important to understand how photoreceptors contribute to non-image-forming visual functions to enable the design of light environments that support optimal circadian rhythm regulation. The purpose of this study was to investigate the contribution of melanopsin-expressing ganglion cells (mRGCs) to circadian rhythm regulation using the silent substitution method, which modulates light stimulus levels to each photoreceptor (mRGC and three types of cones). Night-time saliva melatonin concentrations were measured to assess its contribution to circadian rhythms. We found that melatonin suppression was significantly affected by mRGC stimulation which was modulated by the silent substitution method, especially at time early in melatonin secretion.

In this study, we develop a laser diode model coupled with phosphor; by changing the characteristics of phosphor, we solved the problem related to the emission of harmful blue light while providing light stability. We investigated the effects of the three properties of phosphor conception: density, thickness, and particle size. We obtained smooth blue light distribution by using phosphor.