Light-emitting Diode Light Source Research Articles

LED-based light sources optimised for high colour rendition from an end users’ perspective

Light emitting diode (LED) technology is continuously developing, leading to the current transition from simple phosphor-converted LED lamps to LED lamps optimised for high colour rendition in residential lighting. To assess whether such optimised phosphor-converted LED lamps may fulfil the end users’ needs better than simple phosphor-converted LED lamps we asked participants to rank two particular brands of phosphor-converted LED lamps optimised for high colour rendition, a typical simple phosphor-converted LED lamp and a halogen lamp for pleasantness, naturalness and purchase preference. The results of two experiments suggest that phosphor-converted LED lamps optimised for high colour rendition have the potential to outperform simple phosphor-converted LED lamps and even to measure up to traditional halogen lighting in terms of user preference. However, this is not the case for all phosphor-converted LED lamps optimised for high colour rendition. From the end users’ perspective, unfortunately, it is currently difficult if not impossible to choose the LED light source that one would prefer most. Practitioner Summary: Considering innovations in LED technology, we assessed the potential of LED lamps optimised for high colour rendition to outperform their predecessors regarding user preference. In one of two conditions, these optimised LED lamps outperformed a simple phosphor-converted LED lamp and measured up to halogen lighting. Abbreviations: LED: light emitting diode; CCT: correlated colour temperature; CRI: colour rendering index; CIE: Commission Internationale de l’Éclairage; CRI Ra: CIE General Colour Rendering Index; K: kelvin; lx: lux; GFC: goodness of fit coefficient; BLED80: simple blue-pumped phosphor-converted LED with a CRI Ra of 80; BLED96: blue-pumped phosphor-converted LED optimised for high colour rendition with a CRI Ra of 96; VLED97: violet-pumped phosphor-converted LED optimised for high colour rendition with a CRI Ra of 97; R9: CIE Special Colour Rendering Index for red; ANSI: American National Standards Institute; IES: Illuminating Engineering Society; Rf: IES Fidelity Index; Rg: IES Gamut Index; CC: chromaticity coordinates

Effects of different light sources used for dental operating microscope illumination on the visual function of operators

ObjectivesAdvances in dental operative microscopes (DOMs) enable examination of root canal morphology or detection of root fractures otherwise not visible to the naked eye. However, dental therapy involving prolonged use of DOMs requires precision within a limited visual field, resulting in eye strain among users. This study examined the effects of halogen and light-emitting diode (LED) light sources on asthenopia and visual function following use of DOMs. MethodsThe study used halogen and LED light sources in DOMs. The first experiment was conducted on 6 participants with corrected visual acuity without any organic eye disease. General visual function test (calculation ability test, hand grip strength test, and ophthalmic examination) and subjective symptom questionnaire were used to evaluate the degree of fatigue before and after DOM use. The second experiment was conducted on 9 participants with spherical equivalents within ±4 diopters (D) and astigmatism of 1 D or less. Accommodative function tests (precise test for asthenopia) and a subjective symptom questionnaire (asthenopia) were used before and after use of DOM. ResultsNo significant changes were noted in the degree of fatigue and ophthalmological parameters before and after the procedure with either light source or in between light sources. The tear firm breakup time was shortened after therapy, and a tendency toward dry eyes was observed while using the LED light source. ConclusionsThe halogen and LED light sources used for DOM therapy had similar effects on asthenopia of the operators, with no significant changes in visual function.

Effects of using MgO, CaO additives as sintering aid in pressureless sintering of M2Si5N8:Eu2+ (M = Ba, Sr) phosphor ceramics for amber LED automotive applications

Phosphors have wide applications in many industries, especially the automotive industry. Low efficiency and complex production methods are current challenges of phosphor packaging technology. In this study, M2Si5N8:Eu2+ (M = Ba, Sr) phosphor ceramics (PCs) were developed that exhibited excellent thermal quenching characteristics and a broad wavelength range—580 (yellow)–620 nm (amber)—for use as automotive amber light-emitting diode (LED) light sources. Phosphors— M2Si5N8:Eu2+ (M = Ba, Sr)— with various Ba:Sr compositions were synthesized at 1600 °C. These phosphors were, in turn, used to fabricate PCs; pressureless sintering was aided by the addition of a MgO/CaO—70:30—mixture. The density, microstructure, and optical properties of the phosphors and PCs were analyzed. When the molar concentration of Sr was 0.2 mol, the corresponding phosphor wavelength was 593 nm; these optical characteristics are suitable for amber LED applications. The PC containing 5 wt% sintering aid showed a density of 4.187 g/cm3 and relative density of more than 99%. These sintered PCs demonstrated excellent adaptive optical characteristics that can be used to great effect in automotive LED applications.

Optical design for a cost-effective low-beam headlamp with a white light LED

We present a design for a cost-effective low-beam automotive headlamp with a single light-emitting diode (LED) light source. The proposed design consists of a white LED, an elliptical reflector, a parabolic reflector, a toric lens, a filter, and a prism array. The white LED had a luminous flux of 146 lm. Non-sequential rays were used to improve the efficiency and a toric lens was employed to optimize the light pattern on a 25 m screen which appeared as rectangular with a high degree of uniformity. In addition, the filter and the prism array were modified to correct the measured light pattern results to meet the requirements of ECE R112. We set the reflectivity of the elliptical and parabolic reflectors for the compound reflectors to be 95%. The transmittance of each surface of the toric lens is 98%. The total received lumens was 80.62 lm, and the overall efficiency was 55.22%.

Benzylidene piperidones as photosensitizers for visible light photopolymerization

Benzylidene piperidones (CZ-PD, TPA-PD, and PTZ-PD) with conjugated structure were synthesized by the aldol condensation of aromatic aldehyde and N-benzyl piperidone. These D-π-A-π-D dyes showed good visible light absorption and photosensitizing properties to iodonium salts in visible light-emitting diode (LED) photopolymerization. The photophysical properties of the synthesized structure were investigated via UV–vis spectroscopy and density functional theory (DFT) calculation. The mechanisms of structure-sensitized iodonium salts were explored through steady-state photolysis experiments. Polymerization experiments proved that these dyes with iodonium salt were an effective photoinitiating system for radical photopolymerization under visible LED light source and showed the ability to initiate deep curing.

Smartphone-Based Quantitative Fluorescence Detection of Flowing Droplets Using Embedded Ambient Light Sensor

The detection of fluorescent droplets on the smartphone-based platforms is normally limited by several aspects such as the imaging quality, automaticity, and accessibility. To address the issues, the smartphone-embedded ambient light sensor, which has shown the advantages-including high accuracy, low noise, easy and reliable integration, becomes more and more noted to detect the light intensity variation. In this study, we develop a low-cost and portable smartphone-based platform using the embedded ambient light sensor for flowing fluorescent droplet detection. This platform is simply assembled with a 3D-printed holder and a light-emitting diode (LED) light source powered by the smartphone. Based on the Android system, two applications are self-developed for the performance test and fluorescent droplet detection respectively. After fabricating the droplet generator with off-the-shelf components, fluorescent droplets are generated under different flow rates of the continuous phase and characterized with both the microscopy and the presented platform. And 15 μ L/min was selected as the optimized flow rate of the continuous phase. Finally, the detections of the droplets in different fluorescein concentrations are performed in our smartphone-based platform to confirm its capacity of quantitative analysis. And a linear relationship between the intensity and the concentration with the R square larger than 0.99 is found. We believe that this platform will be a powerful tool in the areas including point-of-care diagnosis, environmental monitoring and food safety. More importantly, it can provide a new sight for the development of novel smartphone-based platforms beyond the embedded cameras.

Efficacy of 5-aminolevulinic acid and LED photodynamic therapy in cervical intraepithelial neoplasia: A clinical trial.

5-Aminolaevulinic acid (5ALA) is a precursor of the strong sensitizer protoporphyrin IX (PpIX) in the heme synthesis pathway. We conducted aclinical trial designed to evaluate the efficacy and safety of 5ALA photodynamic therapy (PDT) using a light-emitting diode (LED) in patients with cervical intraepithelial neoplasia (CIN). Data for 51 CIN patients who underwent 5ALA-PDT between 2012 and 2017 were prospectively analysed. After a 20 % 5ALA jelly formulation was topically applied to the cervix, the region was irradiated with red light at approximately 633 nm to excite PpIX for treatment. We estimated outcomes by cytology, pathology, and human papilloma virus (HPV) testing after PDT. Patients underwent two PDT sessions at one-week intervals during outpatient treatment and achieved favourable results without photosensitivity and severe adverse events. Over a long follow-up period, 96.1 % of all patients showed some positive effects, including approximately 70 % with a complete response (CR), 10 % with a partial response, and 15 % with downgrades. The HPV clearance rate in patients with CR was 79.4 %. Recurrence occurred in five patients who mostly remained HPV-positive after PDT. Based on our study, topical 5ALA-PDT using an LED light source potentially represents a safe treatment for CIN on an outpatient basis.

Haematococcus pluvialis bioprocess optimization: Effect of light quality, temperature and irradiance on growth, pigment content and photosynthetic response

The effect of light quality, using narrow bandwidth light-emitting diode (LED) light sources, irradiance and temperature on the production of green and red cells of Haematococcus pluvialis was studied. The basal optimum conditions selected for astaxanthin accumulation included nitrate starvation, continuous illumination and carbon supply. Monochromatic red light at 20 °C was optimal for green cell production, while astaxanthin accumulation rate was maximal with mixed red and blue light at 30 °C. Under these conditions, astaxanthin productivity reached 25 mg L−1 day−1. Irradiance affected astaxanthin content, but it did not affect the increase in dry weight. The photosynthetic response of H. pluvialis was characterized as complex and highly dependent on the conditions in which the alga is being produced, specially light composition. The use of LEDs for tuning light composition is proven to be a powerful tool to enhance metabolite production.

Establishment and Solution for a Mathematical Model of Multiple Diffuse Reflection

The indirect illumination system with diffuse reflection light-emitting diode (LED) is widely applied in various fields that require high illumination uniformity. On the basis of the Lambertian characteristic of LEDs and the ideal diffuse surface, a design method that features a multiple diffuse reflectance freeform surface is proposed and its related mathematical model is established in this paper. A nonlinear algebraic equation is solved to redistribute the energy emitted by the LED to a uniformity illuminated scene. The outline of the diffuse surface is obtained by solving equations numerically. With the use of the ray tracing software TracePro, simulation results show that the effect is generally the best and the uniformity and efficiency are significantly improved compared with other methods when the proportion between the radius of the target surface and the distance between the LED light source and the target surface is 1:4.

Preparation of poly(methyl methacrylate) microspheres via photopolymerization initiated by LED light source

Poly(methyl methacrylate) (PMMA) microspheres were synthesized through visible light–induced photopolymerization of methyl methacrylate (MMA). 2,4,6-Trimethylbenzoyldipenylphosphine oxide (TPO), polyvinylpyrrolidone (PVP), and light-emitting diodes (LEDs) were used as the photoinitiator, stabilizer, and light source, respectively. No other additive was involved. The effect of LEDs, TPO, and PVP was discussed. Results showed that PMMA microspheres with the size of 0.5–0.8 μm could be obtained when LED@385 nm was the light source, and the content of TPO and PVP was 2 wt% and 30 wt% of MMA. Moreover, the possible formation pathway of PMMA microspheres was proposed based on the investigation of reaction time and addition method of PVP.

Enhancing City Sustainability through Smart Technologies: A Framework for Automatic Pre-Emptive Action to Promote Safety and Security Using Lighting and ICT-Based Surveillance

The scope of the present paper is to promote social, cultural and environmental sustainability in cities by establishing a conceptual framework and the relationship amongst safety in urban public space (UPS), lighting and Information and Communication Technology (ICT)-based surveillance. This framework uses available technologies and tools, as these can be found in urban equipment such as lighting posts, to enhance security and safety in UPS, ensuring protection against attempted criminal activity. Through detailed literary research, publications on security and safety concerning crime and lighting can be divided into two periods, the first one pre-1994, and the second one from 2004–2008. Since then, a significant reduction in the number of publications dealing with lighting and crime is observed, while at the same time, the urban nightscape has been reshaped with the immersion of light-emitting diode (LED) technologies. Especially in the last decade, where most municipalities in the EU28 (European Union of all the member states from the accession of Croatia in 2013 to the withdrawal of the United Kingdom in 2020) are refurbishing their road lighting with LED technology and the consideration of smart networks and surveillance is under development, the use of lighting to deter possible attempted felonies in UPS is not addressed. To capitalize on the potential of lighting as a deterrent, this paper proposes a framework that uses existing technology, namely, dimmable LED light sources, presence sensors, security cameras, as well as emerging techniques such as artificial intelligence (AI)-enabled image recognition algorithms and big data analytics and presents a possible system that could be developed as a stand-alone product to alert possible dangerous situations, deter criminal activity and promote the perception of safety thus linking lighting and ICT-based surveillance towards safety and security in UPS.

Comparison of ophthalmic toxicity of light-emitting diode and organic light-emitting diode light sources

The use of organic light-emitting diodes (OLEDs) has rapidly increased in recent years. However, the effect of OLEDs on human health has not been studied yet. We investigated morphologic and functional changes after OLEDs exposure of human ocular cells, including corneal, conjunctival, lens, and retinal pigment epithelial cells, and mouse eyes. In corneal and conjunctival epithelial cells, the levels of reactive oxygen species production and interleukin-8 expression after white light-emitting diodes (LED) exposure were significantly greater than those after OLED exposure. Although no gross morphologic changes of the eyelid or cornea were found in LED- or OLED-exposed mice, oxidative stress on ocular surface was significantly increased, and the outer nuclear layer (ONL) was significantly shorter in both light-treated groups than the control group. Moreover, ONL thickness was significantly lower in the LED group than the OLED group. The electroretinography response was significantly lower in light exposure group, and there was significant difference between LED- and OLED-treated mice. Although OLED exhibits certain ocular toxicity, it can be less toxic to eyes than LED. The higher blue-wavelength energy of LED light might be the reason for its higher toxicity relative to OLED.

Circadian Potency Spectrum with Extended Exposure to Polychromatic White LED Light under Workplace Conditions.

Electric light has enabled humans to conquer the night, but light exposure at night can disrupt the circadian timing system and is associated with a diverse range of health disorders. To provide adequate lighting for visual tasks without disrupting the human circadian timing system, a precise definition of circadian spectral sensitivity is required. Prior attempts to define the circadian spectral sensitivity curve have used short (≤90-min) monochromatic light exposures in dark-adapted human subjects or in vitro dark-adapted isolated retina or melanopsin. Several lines of evidence suggest that these dark-adapted circadian spectral sensitivity curves, in addition to 430- to 499-nm (blue) wavelength sensitivity, may include transient 400- to 429-nm (violet) and 500- to 560-nm (green) components mediated by cone- and rod-originated extrinsic inputs to intrinsically photosensitive retinal ganglion cells (ipRGCs), which decay over the first 2 h of extended light exposure. To test the hypothesis that the human circadian spectral sensitivity in light-adapted conditions may have a narrower, predominantly blue, sensitivity, we used 12-h continuous exposures of light-adapted healthy human subjects to 6 polychromatic white light-emitting diode (LED) light sources with diverse spectral power distributions at recommended workplace levels of illumination (540 lux) to determine their effect on the area under curve of the overnight (2000–0800 h) salivary melatonin. We derived a narrow steady-state human Circadian Potency spectral sensitivity curve with a peak at 477 nm and a full-width half-maximum of 438 to 493 nm. This light-adapted Circadian Potency spectral sensitivity permits the development of spectrally engineered LED light sources to minimize circadian disruption and address the health risks of light exposure at night in our 24/7 society, by alternating between daytime circadian stimulatory white light spectra and nocturnal circadian protective white light spectra.

Advanced characterization of an optical fibre sensor system based on an MPPC detector for measurement of X-ray radiation in clinical linacs

A reliable, accurate and in-vivo dosimetry system for measuring the radiation dose and profiling the X-ray beam during radiotherapy is reported. Its dynamic range is investigated using an accurately controlled pulsed light emitting diode (LED) system. Highly resolved temporal analog and digital signals were captured from the analog and digital outputs of a multi-pixel photon counter (MPPC) detector when exposed to the LED system. The photon distribution of a low intensity pulsed LED light source was observed and is found to obey a Poisson distribution with changing light intensity. The average number of photons was obtained using the digital MPPC output signals which in turn allowed the appropriate intensity of the light source to be determined for the correct light exposure conditions for the detector. The average analog output voltage over a single 3 μs pulse is determined to indicate the intensity of the detected light. The MPPC detector output analog signal is limited to a narrow range (0.6 V–1.4 V) to ensure adequate signal detection level (the lower limit) and prevention of entry into saturation (the upper limit) which also corresponds to a digital output signal range (in counts). An average photon number range of 3–7 for the digital output signal is established, which leads to the establishment of a unique and constant photon number to average output voltage ratio of 4.64 ± 0.10. Experimental results show that the establishment of this ratio is significant as adherence to it ensures the correct exposure conditions of the MPPC and speeds up the measurement cycle in the clinical setting.

Effects of light-emitting diodes on tissue culture plantlets and seedlings of rice (Oryza sativa L.)

Light-emitting diodes (LEDs) are a new light source with low energy consumption and high photoelectric conversion efficiency, and they can satisfy the energy-saving needs of plant culture systems. However, the effects of LED light sources on rice tissue culture and rice seedling cultivation are poorly understood. This study aimed to evaluate the effects of LEDs on the growth of tissue culture plantlets and seedlings of the rice (Oryza sativa L.) cultivar Nipponbare. The best light source for rice tissue culture was different from that for rice seedling cultivation. Blue (B) LED light was the most appropriate light for rice tissue culture. Under a B LED light, the time required for callus proliferation, differentiation and regeneration was the shortest, and the frequency of plantlet initiation, differentiation and regeneration was the highest. A blue:red (B:R)=1:1 LED light facilitated the growth of rice seedlings and produced the highest chlorophyll and carotenoid contents and photosynthetic rates in the rice seedlings. Abundant photosynthetic products were more effectively generated in the rice seedlings under the B:R=1:1 LED and R LED lights than under the B LED light. B LED light is the most appropriate light for rice tissue culture plantlets and can be used as an alternative light source for rice tissue culture, and B:R=1:1 LED light facilitated the cultivation of robust rice seedlings and can be used as the primary light source for rice factory seedling cultivation.

LED based Fourier transform absorption spectroscopy of H217O in the 14900–15600 cm−1 spectral region

The vibration-rotation absorption spectrum of 17O-enriched water vapor in the range 14900–15600 cm−1 was recorded for the first time by a Fourier Transform Spectrometer coupled to a multi-pass White-type cell providing an optical path length of 34.8 m at room temperature with a spectral resolution of 0.05 cm−1 using high luminance LED (light emitting diode) light source. The high signal-to-noise ratio allowed for the accurate determination of 1047 positions of water lines, of which 661 lines were attributed to the H217O water isotopologue. The rovibrational assignment was based on new variational calculations, which allowed retrieving 285 experimental rotational-vibrational energy levels belonging to twelve vibrational states of the H217O molecule: (410), (330), (311), (231), (212), (151), (033), (052), (113), (132), (180), and (081). The 3ν1+ν2+ν3, 2ν1+3ν2+ν3 and 4ν1+ν2 vibrational bands centered, respectively, at 15325.617, 15095.166 and 15322.533 cm−1, dominate the spectrum. A detailed comparison of the H217O line intensities recorded in this study with observed literature data and with recent high-precision variational calculations showed that the calculated intensities for the (231) - (000) band are weaker by 57% than the experimental ones. The data set obtained in this study will help to improve the quality of variational calculations for water vapor.

Performance Modeling of Ultraviolet Atmospheric Scattering of Different Light Sources Based on Monte Carlo Method

Since the atmosphere has a strong scattering effect on ultraviolet light, the transmission of non-line-of-sight (NLOS) signals can be realized in the atmosphere. In previous articles, ultraviolet (UV) light atmospheric scattering has been characterized by many scattering models based on spot light sources with uniformly distributed light intensity. In order to explore the role of light sources in atmospheric transmission, this work proposed a UV light atmospheric transport model under different types of light source, including light-emitting diode (LED), laser, and ordinary light sources, based on the Monte Carlo point probability method. The simulation of the light source in the proposed model is a departure from the use of a light source with uniform intensity distribution in previous articles. The atmospheric transmission efficiency of different light sources was calculated and compared with the data of existing models. The simulation results showed that the type of light source can significantly change the shape of the received signal and the received energy density. The Monte Carlo (MC) point probability method dramatically reduced the calculation time and the number of photons. The transmission characteristics of different ultraviolet light sources in the atmosphere provide a theoretical foundation for the design of ultraviolet detection and near-ultraviolet signal communication in the future.

Total Internal Reflection Fluorescence Foldscope Adapter: Design, Fabrication and Applications

Fluorescence microscopy is one of the important instruments used in research and clinical laboratories on an everyday basis due to its wide range of applications ranging from a diagnostic tool to a molecular imaging device. However, the high cost, complex instrumentation, and requirement of sophisticated facilities limit its availability to school and college students, especially in developing and underdeveloped countries. In this work, we report the design and development of a slide-like portable total internal reflection fluorescence (TIRF) adapter, which can be integrated easily with Foldscope (a paper microscope) to observe and capture the fluorescence images using any smartphone. The adapter consists of a battery-powered LED (light source), a small piece of multimode optical fiber, a slide-like 3-D printed waveguide platform to hold the optical fiber and light emitting diode (LED) at an appropriate position. The potential of the adaptor is validated by capturing the fluorescence images of two most commonly used dyes i.e. fluorescein isothiocyanate (FITC) and rhodamine-B, after being immobilized on amine-functionalized optical fiber probe. Further, this adaptor is successfully used to demonstrate (i) Forster resonance energy transfer phenomenon by employing FITC dye as donor and gold nanoparticles as quencher moiety and (ii) fluorescence bioassay by observing antigen-antibody interactions using human immunoglobulin G as the receptor and FITC-tagged goat anti-human immunoglobulin G as analyte. The inexpensive, portable and user-friendly TIRF adapter is a potential alternative to conventionally used fluorescence microscopes, especially for the school and college students and in resource-constrained clinical laboratories.

High-power light-emitting diode array design and assembly for practical photodynamic therapy research.

.Significance: Commercial lasers, lamps, and light-emitting diode (LED) light sources have stimulated the clinical translation of photodynamic therapy (PDT). Yet, the continued exploration of new photosensitizers (PSs) for PDT often requires separate activation wavelengths for each agent being investigated. Customized light sources for such research frequently come at significant financial or technical cost, especially when compounded over many agents and wavelengths.Aim: LEDs offer potential as a cost-effective tool for new PS and multi-PS photodynamic research. A low-cost-per-wavelength tool leveraging high-power LEDs to facilitate efficient and versatile research is needed to further accelerate research in the field.Approach: We developed and validated a high-power LED array system for benchtop PDT with a modular design for efficient switching between wavelengths that overcome many challenges in light source design. We describe the assembly of a low-cost LED module plus the supporting infrastructure, software, and protocols to streamline typical in vitro PDT experimentation.Results: The LED array system is stable at intensities in excess of with 2.3% variation across the illumination field, competitive with other custom and commercial devices. To demonstrate efficacy and versatility, a primary ovarian cancer cell line was treated with two widely used PSs, aminolevulinic acid and verteporfin, using the LED modules at a clinically relevant light dose that induced over 90% cell death for each treatment.Conclusions: Our work provides the community with a tool for new PS and multi-PS benchtop photodynamic research that, unlike most commercial light sources, affords the user a low barrier to entry and low-cost-per-wavelength with the goal of illuminating new insights at the forefront of PDT.

Making Soft Optical Sensors More Wearable

This paper discusses new components and approaches to make stretchable optical fiber sensors better meet the power and washability requirements of wearables. First, an allpolymer quick connector allows the light source and photosensor to be quickly detached for washing. Second, the paper investigates the possibility of driving the sensors using ambient light instead of an onboard light source. While optical strain sensors and touch sensors have advantages over electronic ones in wet environments, and the intrinsic stretchability of the fibers is useful for soft robotics and highly conformal wearables, the typical light-emitting diode (LED) light source consumes more power than an electronic resistive or capacitive strain sensor. In this work, ambient light of uniform but unknown intensity is demonstrated to drive an elastomeric optical touch sensor in a differential configuration.