The effect of power bleaching actived by several light sources on enamel microhardness

The purpose of this study was to evaluate the influence of different light sources for in-office bleaching on surface microhardness of human enamel. One hundred and five blocks of third molars were distributed among seven groups. The facial enamel surface of each block was polished and baseline Knoop microhardness of enamel was assessed with a load of 25 g for 5 s. Subsequently, the enamel was treated with 35% hydrogen peroxide bleaching agent and photo-activated with halogen light (group A) during 38 s, LED (group B) during 360 s, and high intensity diode laser (group C) during 4 s. The groups D (38 s), E (360 s), and F (4 s) were treated with the bleaching agent without photo-activated. The control (group G) was only kept in saliva without any treatment. Microhardness was reassessed after 1 day of the bleaching treatment, and after 7 and 21 days storage in artificial saliva. The mean percentage and standard deviation of microhardness in Knoop Hardness Number were: A 97.8 ± 13.1 KHN; B 95.5 ± 12.7 KHN; C 84.2 ± 13.6 KHN; D 128.6 ± 20.5 KHN; E 133.9 ± 14.2 KHN; F 123.9 ± 14.2 KHN; G 129.8 ± 18.8 KHN. Statistical analysis (p < 0.05; Tukey test) showed that microhardness percentage values were significantly lower in the groups irradiated with light when compared with the non-irradiated groups. Furthermore, the non-irradiated groups showed that saliva was able to enhance the microhardness during the measurement times. The enamel microhardness was decreased when light sources were used during the bleaching process and the artificial saliva was able to increase microhardness when no light was used.     

Study of the Light Emitting Diode as a photoreceptor: Spectral and electrical characterization as function of temperature and lighting source

In this study, the temperature influence on the spectral responsivity of a Light Emitting Diode (LED) used as a photoreceptor, combined to light source spectrum is correlated to electrical characteristics in order to propose an alternative method to estimate LED junction temperature, regardless of the absolute illumination intensity and based on the direct correlation between the integral of the product of two optical spectra and the photo-generated currents. A laboratory test bench for experimental optical measurements has been set in order to enable any characterizing of photoelectric devices in terms of spectral behaviour, in a wavelength range placed between 400–1000?nm, and of current-voltage characteristics as function of temperature by using two different illumination sources. The temperature is analysed in a range from 5?°C up to 85?°C, so as to evaluate thermal variation effects on the sensor performance. The photo-generated current of two LEDs with different peak wavelengths has been studied. Research has observed and mathematically analysed what follows: since the photo-generated current strictly depends on the combination between the spectral response of the photoreceptor and the lighting source response, it becomes possible to estimate indirectly the junction temperature of the LEDs by considering the ratio between the photogenerated currents obtained by using two different illumination sources. Such results may for one thing increase knowledge in the fields where LEDs are used as photo-detectors for many applications and for another, they could be extended to generic photodetectors, thus providing useful information in photovoltaic field, for instance.     

Thermal optimization of high power LED arrays with a fin cooling system

In this paper, we describe an optimization process of thermal design for the light lamp which utilizes the Light Emitting Diode (LED) module as a lighting source. The thermal performance of the LED module was shown to significantly improve by the optimization process of cooling system attached with it. A wind circulating cooling system was designed for the LED arrays with the input power of 60?Watts and another heat pipe cooling system was designed for the input power of 144?Watts. The effects of design parameters such as air temperature and air velocity on the thermal performance of LED lamp were investigated. Thermal performance of the two cooling systems was compared for practical application.     

Light-emitting diodes for space applications

The use of Light Emitting Diode (LED) devices for illumination inside space cabin and outside have been well exploited in the past few years; these include, for example, the in-cabin application on the bio-science satellite in 2007 and the out-of cabin application on spacecraft in 2008 to shine on the first step in space of Chinese astronaut. The simulation of the optical properties has been performed to optimize the brightness of the LED lamp. The thermal property of assembled LED lamp has been experimentally characterized and used in combination with the numerical simulation to improve the precision of determining the active layer temperature of the LEDs packed in the lamp. The measurement precision of the LED active layer temperature is improved to a value better than 1 K.     

Changes in the temperature of a dental light-cured composite resin by different light-curing units

The purpose of this study was to evaluate the temperature increase during the polymerization process through the use of three different light-curing units with different irradiation times. One argon laser (Innova, Coherent), one halogen (Optilight 501, Demetron), and one blue LED (LEC 1000, MM Optics) LCU with 500 mW/cm² during 5, 10, 20, 30, 40, 50, and 60 s of irradiation times were used in this study. The composite resin used was a microhybrid Filtek Z-250 (3M/ESPE) at color A₂. The samples were made in a metallic mold 2 mm in thickness and 4 mm in diameter and previously light-cured during 40 s. A thermocouple (Model 120–202 EAJ, Fenwal Electronic, Milford, MA, USA) was introduced in the composite resin to measure the temperature increase during the curing process. The highest temperature increase was recorded with a Curing Light 2500 halogen LCU (5 and 31°C after 5 and 60 s, respectively), while the lowest temperature increase was recorded for the Innova LCU based on an argon laser (2 and 11°C after 5 and 60 s, respectively). The temperature recorded for LCU based on a blue LED was 3 and 22°C after 5 and 60 s, respectively. There was a quantifiable amount of heat generated during the visible light curing of a composite resin. The amount of heat generated was influenced by the characteristics of the light-curing units used and the irradiation times.     

Temperature corresponding to ultrasonic velocity maximum studies in aqueous solutions

Ultrasonic velocities in aqueous solutions of acetamide, dimethyl urea andβ-alanine at different concentrations in the temperature range of about 60°C to 80°C have been measured using an interferometer technique with an accuracy of ±0.003%. The temperature corresponding to velocity maximum at different concentrations is evaluated with an accuracy of ±0.2°C. The results are discussed in the light of the structure-breaking property of these substances in water.     

LED照明自适应驱动电源的研制

针对半导体发光二极管(LED)作为照明的驱动特性,设计了一种基于开关电源的自适应LED驱动电路。利用高密度电源控制芯片sa7527实现了LED的恒流驱动和过压保护,通过对输出光强和LED温度的检测实现了光衰的自动补偿功能。实际应用表明,该驱动电路可满足LED作为照明的实际需要,并且具有宽电压输入范围、高效率和光衰补偿功能。     

用于标定CCD相机的高精度数控LED点光源

介绍了一种以发光二极管（LED）点光源作为相机标定光源的方法。根据LED点光源的特性,用恒流源给LED点光源提供所需的电流,用光照度计测量LED光源的光强度。由ARM单片下位机控制恒流源;通过串行通讯与上位机交换数据;由计算机作为上位机来管理数控恒流源和光照度计;根据所测光度值来调节电流,直到光度达到预想值。实验分析显示：LED点光源作为标定光源可以达到CCD标定的要求,精度也较高,能够很好地自适应控制LED的光照强度,达到了预期的效果,且系统使用方便灵活,性能稳定可靠。     

In vitro photodynamic antimicrobial chemotherapy in dentine contaminated by cariogenic bacteria

The development of a method to ensure bacterial-free substrates without extensive cavity preparation would be highly useful to dentistry, since there is no currently available effective method for killing residual bacteria in dentinal tissue. This randomized in vitro study determined parameters for using toluidine blue O (TBO) with a light-emitting diode (LED) for dentine caries disinfection and monitored intrapulpal/periodontal temperatures during irradiation. Occlusal human dentine slabs were immersed in Streptococcus mutans culture for demineralization induction. Slabs were allocated to 10 groups (n = 15), which were treated with 0.1 mg ml⁻¹ TBO with 5 min of incubation time or 0.9% NaCl solution for 5, 10 or 15 min, and submitted or not to irradiation for 5, 10 or 15 min (47, 94, and 144 J/cm²). Before and after treatments, dentine samples were analyzed with regard to S. mutans counts. In whole teeth, temperature in pulp and periodontium was measured by thermocouples during irradiation. Kruskal-Wallis/Student-Newman-Keuls, and ANOVA/Tukey test were respectively utilized to compare log reductions and temperature rises between groups. Bacterial reduction was observed when dentine was exposed to both TBO and LED at all irradiation times, as well as to LED alone for 10 and 15 min. Temperature increases lower than 2°C were observed for either pulp or periodontium. Concluding, LED combined with TBO is a safe and effective approach for dentine caries disinfection. Nevertheless, additional studies should be conducted to determine the influence of the irradiation in S. mutans viability in dentinal surface/tubules.     

Study on the temperature dependence of BGO light yield

The temperature dependence of BGO coupled with photomultiplier tube R5610A-01 was studied in the range of-30–30℃. The temperature coefficient of the BGO and R5610 A as a whole was tested to be-1.82%/℃. And the temperature coefficient of the gain of the R5610 A is-0.44%/℃ which was tested in the same situation using a blue LED. Thus the temperature coefficient of BGO's light yield can be evaluated as-1.38%/℃.     

Effect of pre-heating resin composite and light-curing units on monomer conversion

The purpose of this study was to evaluate the effect of pre-heating resin composite photo-cured with light-curing units (LCU) by FT-IR. Twenty specimens were made in a metallic mold (4 mm diameter × 2 mm thick) from composite resin—Tetric Ceram® (Ivoclar/Vivadent) at room temperature (25°C) and pre-heated to 37, 54, and 60°C. The specimens were cured with halogen curing light (QTH) and light emitted by diodes (LED) during 40 s. Then, the specimens were pulverized, pressed with KBr and analyzed with FT-IR. The data were submitted to statistical analysis of variance and Kruskal-Wallis test. Study data showed no statistically significant difference to the degree of conversion for the different light curing units (QTH and LED) (p > 0.05). With the increase of temperature there was significant increase in the degree of conversion (p < 0.05). In this study were not found evidence that the light curing unit and temperature influenced the degree of conversion.     

组合式发光二极管路灯反射器的设计

设计了一组合式路灯反射器,以使发光二极管（LED）路灯在道路照明时产生矩形光斑和均匀照度。在非成像光学基础上,利用复合抛物面的高性能集光作用和机械设计软件的强大作图功能,设计了一款分段组合复合抛物面反射器（CPC）。基于“边缘光线原理”和”裁剪法”,此款反射器能将朗伯型发光的LED光束整形为近似矩形分布,出光效率达96％以上。理论模拟证明：在高度为10m,范围为10m×30m内利用此反射器进行二次配光的LED路灯的照度均匀度达0．5以上。该反射式LED路灯光束整形器结构简单,光学效率高、成本低廉,模拟结果完全达到了目前我国国家道路照明规范要求。     

The development of an inspection system for defects in silicon crystal growth

This study presents an inspection system to detect the growth defects of silicon crystals that comprise a CCD camera, an LED light source, and power modulation. The defects on multicrystalline silicon can be observed clearly while the silicon wafer were irradiated by the red LED light at a small lighting angle (i.e., 20–30°). However, the growth defects on monocrystalline silicon wafer were difficult to observe because of it low image intensity. And then, the growth defects image was significantly enhanced when the wafer was illuminated by a white LED (WLED) and rotated at a specific angle (i.e., 23°). The experimental results showed that the WLED illumination system made the growth defects more easily observable than did other LED sources (i.e., red, blue, and green LEDs). In addition, the proposed inspection system can be used for on-line fast detection for quality control of monocrystalline silicon wafer.     

Evidence for ordered regions in poly(n-butyl)methacrylate from light-scattering studies

From light-scattering studies on polybutylmethacrylate, a polymeric glass, the variation of the velocity and attenuation of thermally excited hypersonic phonons with temperature has been measured. Measurement of the temperature dependence of the ratio of the intensity of the Rayleigh line to the Brillouin lines is interpreted as due to a configurational rearrangement within the glass above the glass transition temperature, T_g . Only light scattered from longitudinal phonons was observed. The distinct change in the temperature dependence of the velocity, attenuation and intensity ratio identified the glass transition.

For samples annealed well above T_g, T_g was found to be about 0°C from the light-scattering studies, 12°C from differential scanning calorimetry (DSC), and 20°C from refractive index measurements. For an unannealed sample the behaviour of the above parameters with temperature was found to be different. T_g for the unannealed sample was 14°C from light-scattering, 18°C from DSC and 20°C from index of refraction measurements.     

Effect of power densities and irradiation times on the degree of conversion and temperature increase of a microhybrid dental composite resin

The different parameters used for the photoactivation process provide changes in the degree of conversion (DC%) and temperature rise (TR) of the composite resins. Thus, the purpose of this study was to evaluate the DC (%) and TR of the microhybrid composite resin photoactivated by a new generation LED. For the KBr pellet technique, the composite resin was placed into a metallic mould (1-mm thickness and 4-mm diameter) and photoactivated as follows: continuous LED LCU with different power density values (50–1000 mW/cm²). The measurements for the DC (%) were made in a FTIR Spectrometer Bomen (model MB-102, Quebec-Canada). The spectroscopy (FTIR) spectra for both uncured and cured samples were analyzed using an accessory for the diffuse reflectance. The measurements were recorded in the absorbance operating under the following conditions: 32 scans, 4-cm^?1 resolution, and a 300 to 4000-cm^?1 wavelength. The percentage of unreacted carbon-carbon double bonds (% C=C) was determined from the ratio of the absorbance intensities of aliphatic C=C (peak at 1638 cm^?1) against an internal standard before and after the curing of the specimen: aromatic C-C (peak at 1608 cm^?1). For the TR, the samples were made in a metallic mould (2-mm thickness and 4-mm diameter) and photoactivated during 5, 10, and 20 s. The thermocouple was attached to the multimeter to allow the temperature readings. The DC (%) and TR were calculated by the standard technique and submitted to ANOVA and Tukey’s test (p < 0.05). The degree of conversion values varied from 35.0 (±1.3) to 45.0 (±2.4) for 5 s, 45.0 (±1.3) to 55.0 (±2.4) for 10 s, and 47.0 (±1.3) to 52.0 (±2.4) for 20 s. For the TR, the values ranged from 0.3 (±0.01) to 5.4 (±0.11)°C for 5 s, from 0.5 (±0.02) to 9.3 (±0.28)°C for 10 s, and from 1.0 (±0.06) to 15.0 (±0.95)°C for 20 s. The power densities and irradiation times showed a significant effect on the degree of conversion and temperature rise.     

Long-range effect of light on the microhardness of annealed molybdenum foils

It is shown that, when irradiated by light on one side, both as-prepared samples of molybdenum foil and those annealed in the temperature range 75–900°C change their microhardness on the other (nonirradiated) side. Annealing influences the relative variation in the microhardness under the action of a single irradiation and multiple irradiations, the changes being dependent on the annealing temperature. Recrystallization annealing increases the relative change in the microhardness and makes the microhardness variation under irradiation-relaxation cycling regular, whereas low-temperature annealing breaks this regularity. The results demonstrate that the state of defects in the initial state of the metal is of crucial importance in the phenomenon.     

ZnO nanorods–polymer hybrid white light emitting diode grown on a disposable paper substrate

We demonstrate intrinsic white light emission from hybrid light emitting diodes fabricated using an inorganic–organic hybrid junction grown at 50 °C on a paper substrate. Cyclotene was first spin coated on the entire substrate to act as a surface barrier layer for water and other nutrient solutions. The active area of the fabricated light emitting diode (LED) consists of zinc oxide nanorods (ZnO NRs) and a poly(9,9‐dioctylfluorene) (PFO) conducting polymer layer. The fabricated LED shows clear rectifying behavior and a broad band electroluminescence (EL) peak covering the whole visible spectrum range from 420 nm to 780 nm. The color rendering index (CRI) was calculated to be 94 and the correlated color temperature (CCT) of the LED was 3660 K. The low process temperature and procedure in this work enables the use of paper substrate for the fabrication of low cost ZnO–polymer white LEDs for applications requiring flexible/disposable electronic devices. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

温度和电流对白光LED发光效率的影响

对大功率白光LED发光效率进行了研究,得出温度和电流对LED发光效率的影响:随着温度的升高,势阱中辐射复合几率降低,从而降低了发光效率;电流的升高,使更多的非平衡载流子穿过势垒,降低了发光效率。LED工作时,过高的工作温度或者过大的工作电流都会产生明显的光衰:如果LED工作温度超过芯片的承载温度,这将会使LED的发光效率快速降低,产生明显的光衰,并且对LED造成永久性破坏;如果LED的工作电流超过芯片的饱和电流,也会使LED发光效率快速降低,产生明显的光衰。并且LED所能承载的温度与饱和电流有一定关系,散热良好的装置可以使LED工作温度相对降低些,饱和电流也可以更大,LED也就可以在相对较大的电流下工作。     

光束质量对闪烁和流速测量的影响分析

给出了用发光二极管测量闪烁和流速光源远场理想特性的表达式.波前扭曲可以分解成波前倾斜和曲率改变两部分来处理.波前倾斜和离轴接收信号的情况相当,对测量结果影响不大.当波前曲率半径不等于到光源的距离时,对流速和闪烁强度测量都会带来不能忽略的误差,路径加权函数的对称特性也会改变.最后给出的流速测量的实验结果和理论计算是一致的.     

Si基Ge异质结构发光器件的研究进展

近年来,与Si的CMOS工艺相兼容的Ge/Si异质结构发光器件取得很多重要的进展。本文概述了Si基Ge异质结构发光器件的最新成果,如Ge/Si量子点发光二极管、Si衬底上的Ge发光二极管及激光器和Ge/SiGe多量子阱发光二极管,分别描述了这些器件的特点和增强其发光特性的途径。最后展望了Si基Ge异质结构发光器件的发展趋势,指出尽管Si基Ge异质结构发光器件获得了很大的发展,但是器件的发光效率仍然很低,离实用还有一定距离,还需要在材料和器件的结构方面有更多的创新。