Generation Of Light-emitting Diodes Research Articles

Effects of different LED light curing units on the degree of conversion and microhardness of different composites: FT-IR and SEM-EDX analysis

The aim of this study was to evaluate the degree of conversion (DC), Vickers microhardness (VHN), main components and surface properties of a microhybrid and two bulk-fill composite resins polymerized with second and third generation light emitting diodes (LED). Sixty cylindrical specimens of Filtek™ Bulk-Fill, everX Posterior (bulk technique) and Filtek Z250 (incremental technique) were prepared in plexiglass molds (5 mm in diameter and 4 mm in thickness) and cured with second-generation LED (Woodpecker LED.B) and third-generation LED (Valo) resulting in six groups (n = 10). DC was determined using Fourier transform infrared spectroscopy (FT-IR), and VHN with Vickers microhardness tester. The main components were identified by means of energy-dispersive X-ray spectroscopy (EDX) microanalysis; whereas filler particles and surface properties were analyzed by scanning electron microscopy (SEM). VHN and DC data were analyzed using two-way ANOVA, followed by t-test with Bonferroni correction for pairwise comparison (p < 0.05). When DC and VHN values were evaluated, after polymerization with second and third generation LED, there was a statistical difference in bulk-fill composites, while there was no statistical difference in microhybrid composite. While, the highest DC and VHN values were obtained after polymerization of Filtek Z250 with Valo, the lowest DC and VHN values were obtained with Filtek Bulk-Fill with Woodpecker LED.B. The degree of conversion and microhardness are affected by the structure of the composite resin and LEDs.

Shape-controlled synthesis of CsPbBr3 nanorods with bright pure blue emission and high stability

CsPbBr3 NRs synthesized at 80 °C show bright blue emission at 462 nm and exhibit a high PLQY of 62.65%. The 1 : 1 mixed anti-solvents of EAC and IPA can change the state of NR surface ligands and improve the stability of NRs.

Conventional and Inverted Light-Emitting Diodes with 386 nm Emission Wavelength Based on Metal-Free Carbon Dots

Ultraviolet (UV) light-emitting diodes (LEDs) are of great concern due to wide applications in the fields of solid-state displays, photocommunication, and scientific and medical instruments. During the past 10 years, organic and inorganic semiconductors have made great breakthroughs in short-wavelength emission. Nowadays, carbon dots (CDs), which possess distinctive superiorities of high stability, nontoxicity, and low cost, are promising all-band emission materials for the next generation of LEDs. However, the fabrication of CD-based LEDs (CD-LEDs) with emission wavelengths below 400 nm is still a huge limitation in this field. Herein, we prepared UV emission CDs with the photoluminescence emission wavelength of 371 nm. The UV-CDs are perfectly compatible with both conventional and inverted device structures so as to realize the currently shortest electroluminescent emission wavelength of 386 nm for CD-LEDs. The conventional UV-CD-LEDs possess the optimum luminance of 268 cd m-2 (5427 W sr-1 m-2) with an external quantum efficiency (EQE) of 1.115%. Meanwhile, the inverted UV-CD-LEDs possess the optimum luminance of 132 cd m-2 (2673 W sr-1 m-2) with an EQE of 0.869%. This work paves a new road to manufacture carbon nanomaterial-based UV emission devices with high luminance, EQE, and stability.

Facile synthesis of KaCs1−aPbBr3@ molecular sieve SBA-15 composite with improved luminescence and wet/thermal stability

CsPbX3 (XCl, Br, I) perovskite quantum dots (PeQDs) have excellent properties, which makes it the most promising optoelectronic materials for the next generation of light-emitting diodes (LEDs) and display devices fields. However, CsPbX3 PeQDs have poor-term stability and easily decompose in moist or heat conditions. In this paper, the KaCs1−aPbBr3 @SBA-15 composite was prepared at room temperature. Alkali metal ion doping can enhance the luminous intensity and tune the emission spectrum of CsPbBr3 PeQDs, while the introduction of the SBA-15 matrix improves the stability of the KaCs1−aPbBr3 PeQDs (a=0, 0.1, 0.25, 0.35, 0.4, 0.45). When the molar ratio of K+/Cs+ is 0.4 / 0.6, the PL intensity of CsPbBr3 PeQDs increased by 21.4%. The luminous intensity of K0.4Cs0.6PbBr3 @SBA-15 composite is further increased by 18.8% compared to the K0.4Cs0.6PbBr3 PeQDs, and its moisture and heat resistance are significantly improved. The PL intensity of K0.4Cs0 6PbBr3 @SBA-15 can maintain 52% of the initial brightness after immersion in deionized water for 21 days, as well as reaching 95% of the initial value in the heating/cooling cycle treatment. Such excellent properties make the KaCs1−aPbBr3 @SBA-15 composite an ideal material for lighting and display applications.

A study of negative-thermal-quenching (Ba/Ca)AlSi5O2N7:Eu2+ phosphors.

Phosphor is an important part of the new generation of light-emitting diodes (LEDs), which requires high luminous intensity and high-temperature resistance. In this study, a series of excellent (Ba1-x-yCax)AlSi5O2N7:yEu2+ phosphors was developed, which were synthesized by a high-temperature solid-state reaction in a reducing atmosphere. In addition, the crystallinity and luminescence intensity of the samples could be enhanced by some amount of Ca2+ substitution. The luminescence intensity was the highest when the Eu2+ concentration reached 0.06. Furthermore, the thermal stability of the luminescence was studied in detail. The results were satisfactory, showing that the luminescence intensity of the (Ba1-xCax)AlSi5O2N7:Eu2+ phosphors exhibited unique negative-thermal-quenching characteristics both at high (273-473 K) and low (4-273 K) temperatures. And the phosphor combined with UV LED chip and red phosphor Sr2Si5N8:Eu2+ can achieve a CRI of 90.4 in white LED application which indicated the (Ba1-xCax)AlSi5O2N7:Eu2+ phosphor has potential in LED applications.

Electrochemical Charging Effect on the Optical Properties of InP/ZnSe/ZnS Quantum Dots.

Semiconductor quantum dots (QDs) are spotlighted as a key type of emissive material for the next generation of light-emitting diodes (LEDs). This work presents the investigation of the electrochemical charging effect on the absorption and emission of the InP/ZnSe/ZnS QDs with different mid-shell thicknesses. The excitonic peak is gradually bleached during electrochemical charging, which is caused by 1Se (or 1Sh ) state filling when the electron (or hole) is injected into the InP core. Additional charges also lead to photoluminescence (PL) intensity reduction, however, it is greatly mitigated as the mid-shell thickness increases. Various PL measurements reveal that the PL reduction under electrochemical charging is attributed to the acoustic phonon-assisted Auger recombination. Here, the Auger recombination in QDs with a thick mid-shell is reduced under the electrochemically charged condition, indicating that QDs with larger volume are more stable emitters in charge-injecting devices such as LEDs. Furthermore, the negative and positive trion Auger recombination rate constants are estimated, respectively, via electrochemical charging. The negative trion Auger rate constants decrease with an increase in the mid-shell thickness increases, whereas the positive trion Auger rate constants are not heavily reliant on the mid-shell thickness.

Enhancing photoluminescence quantum efficiency of metal halide perovskites by examining luminescence-limiting factors

Metal halide perovskites (MHPs) show superior optoelectronic properties, which give them the great potential for use in next generation light-emitting diodes (LEDs). In particular, their narrow emission linewidths can achieve ultrahigh color purity. However, the reported luminescence efficiency (LE) values are not high enough to be commercialized in displays and solid-state lightings. Moreover, the operational stability of LEDs associated with the overshooting of luminance and the high relative standard deviation of reported external quantum efficiencies are still problematic. In this perspective, we review photophysical factors that limit the photoluminescence quantum efficiency of perovskite-based LEDs. These factors are categorized into (i) weak exciton binding, (ii) nonradiative recombinations, (iii) slow cooling of long-lived hot carriers, (iv) deep-level defects, and (v) interband transition rates. We then present various physicochemical methods to effectively overcome these luminescence-limiting factors. We finally suggest some useful research directions to further improve the LE of MHP emitters as core components in displays and solid-state lightings.

Optical characterization of magnesium incorporation in p-GaN layers for core–shell nanorod light-emitting diodes

III-nitride nanostructures are of interest for a new generation of light-emitting diodes (LEDs). However, the characterization of doping incorporation in nanorod (NR) structures, which is essential for creating the p-n junction diodes, is extremely challenging. This is because the established electrical measurement techniques (such as capacitance–voltage or Hall-effect methods) require a simple sample geometry and reliable ohmic contacts, both of which are difficult to achieve in nanoscale devices. The need for homogenous, conformal n-type or p-type layers in core–shell nanostructures magnifies these challenges. Consequently, we demonstrate how a combination of non-contact methods (micro-photoluminescence, micro-Raman and cathodoluminescence), as well as electron-beam-induced-current, can be used to analyze the uniformity of magnesium incorporation in core–shell NRs and make a first estimate of doping levels by the evolution of band transitions, strain and current mapping. These techniques have been used to optimize the growth of core–shell nanostructures for electrical carrier injection, a significant milestone for their use in LEDs.

Continuous gas-phase synthesis of nanowires with tunable properties

Semiconductor nanowires are key building blocks for the next generation of light-emitting diodes, solar cells and batteries. To fabricate functional nanowire-based devices on an industrial scale requires an efficient methodology that enables the mass production of nanowires with perfect crystallinity, reproducible and controlled dimensions and material composition, and low cost. So far there have been no reports of reliable methods that can satisfy all of these requirements. Here we show how aerotaxy, an aerosol-based growth method, can be used to grow nanowires continuously with controlled nanoscale dimensions, a high degree of crystallinity and at a remarkable growth rate. In our aerotaxy approach, catalytic size-selected Au aerosol particles induce nucleation and growth of GaAs nanowires with a growth rate of about 1 micrometre per second, which is 20 to 1,000 times higher than previously reported for traditional, substrate-based growth of nanowires made of group III-V materials. We demonstrate that the method allows sensitive and reproducible control of the nanowire dimensions and shape--and, thus, controlled optical and electronic properties--through the variation of growth temperature, time and Au particle size. Photoluminescence measurements reveal that even as-grown nanowires have good optical properties and excellent spectral uniformity. Detailed transmission electron microscopy investigations show that our aerotaxy-grown nanowires form along one of the four equivalent〈111〉B crystallographic directions in the zincblende unit cell, which is also the preferred growth direction for III-V nanowires seeded by Au particles on a single-crystal substrate. The reported continuous and potentially high-throughput method can be expected substantially to reduce the cost of producing high-quality nanowires and may enable the low-cost fabrication of nanowire-based devices on an industrial scale.

Light emitting diodes: Light engines to simplify and economize advanced microscopy

THE old adage, ‘‘A picture is worth a thousand words,’’ is especially true in biological research, with microscopic images serving to mark the development of key concepts in biology since Hooke first described ‘‘cells’’ in thin slices of cork (1). More than 400 years later, microscopic imaging still serves as a primary data source for biological research, with increasingly advanced techniques that provide information on molecular scale interactions and dynamics. Such advanced molecular imaging techniques take advantage of ever more sophisticated light sources, optics, detectors, and image processing methods, many of which can be quite complex and expensive. At the same time, new technologies and production methods, many driven by the consumer market, have resulted in key components of imaging systems becoming smaller, simpler, and cheaper. The convergence of these effects is having profound effects on our options for light sources for microscopic imaging. The properties of the illumination source are critical to many advanced optical microscopy methods. Lasers play a key role in many of these owing to the monochromatic and coherent nature of their light, plus their ability to be pulsed and otherwise controlled. However, illumination with high-pressure mercury gas discharge or xenon lamps is still the standard for most imaging applications. These light sources provide bright, broad-spectrum excitation (300–900 nm) that can be easily selected by excitation filters for fluorescent imaging applications. However, there are quite a few disadvantages that limit the wide-spread of mercury or xenon lamps-based microscopy system in biological applications. First, sometimes these traditional light sources are too bright and harmful for the living organisms being studied. Excessive brightness can cause rapid photo-bleaching of the dyes used to stain the cells/ tissues. UV light especially, if not blocked, can have significant deleterious effects on live cells. Second, there are substantial costs involved in using mercury or xenon lamps because of their relatively short lifespan. The life of a mercury lamp is usually several hundred hours, and the intensity of these lamps decays progressively during this time. In addition, gas discharge lamps require some time to warm up before lamp intensity reaches steady state. Therefore, once mercury lamps are turned on, they have to be left on for hours to enable fluorescent measurements as needed without delay, thereby further shortening the lamp lifetime. Third, there are also some hazards issues of using mercury or xenon lamps. These lamps generate a significant amount of heat and therefore introduce complications when used in a confined space. When mercury lamps die, they can explode and damage the lenses or mirrors within the lamp housing. These factors combine to make gas discharge lamps inconvenient for lab-based applications and impractical for field applications, including use in portable, miniature, or low cost imaging devices. By contrast, light-emitting diodes (LEDs) show great pro

IS LIGHT-EMITTING DIODE PHOTOTHERAPY (LED-LLLT) REALLY EFFECTIVE?

Low level light therapy (LLLT) has attracted attention in many clinical fields with a new generation of light-emitting diodes (LEDs) which can irradiate large targets. To pain control, the first main application of LLLT, have been added LED-LLLT in the accelerated healing of wounds, both traumatic and iatrogenic, inflammatory acne and the patient-driven application of skin rejuvenation. Rationale and Applications: The rationale behind LED-LLLT is underpinned by the reported efficacy of LED-LLLT at a cellular and subcellular level, particularly for the 633 nm and 830 nm wavelengths, and evidence for this is presented. Improved blood flow and neovascularization are associated with 830 nm. A large variety of cytokines, chemokines and macromolecules can be induced by LED phototherapy. Among the clinical applications, non-healing wounds can be healed through restoring the collagenesis/collagenase imbalance in such examples, and 'normal' wounds heal faster and better. Pain, including postoperative pain, postoperative edema and many types of inflammation can be significantly reduced. Experimental and clinical evidence: Some personal examples of evidence are offered by the first author, including controlled animal models demonstrating the systemic effect of 830 nm LED-LLLT on wound healing and on induced inflammation. Human patients are presented to illustrate the efficacy of LED phototherapy on treatment-resistant inflammatory disorders. Provided an LED phototherapy system has the correct wavelength for the target cells, delivers an appropriate power density and an adequate energy density, then it will be at least partly, if not significantly, effective. The use of LED-LLLT as an adjunct to conventional surgical or nonsurgical indications is an even more exciting prospect. LED-LLLT is here to stay.

Effect of Curing Lights and Bleaching Agents on Physical Properties of a Hybrid Composite Resin

The aim of this in vitro study was to evaluate the microhardness (MH) and diametral tensile strength (DTS) of a minifill hybrid composite (Filtek Z250, 3M ESPE), polymerized with halogen lamp or second generation light-emitting diode (LED), submitted to different bleaching agents. Composite resin specimens were randomly polymerized according to experimental groups (halogen, 550 mW/cm(2)/20 seconds; LED, 550 mW/cm(2)/25 seconds) and subdivided into three subgroups (N=8): A, without bleaching (control); H, 35% hydrogen peroxide; and C, 16% carbamide peroxide. After that, the MH test and DTS test were performed. Two-way analysis of variance (whitening x light) and Tukey's tests (alpha=5%) were performed. For DTS, there were no statistical differences among the bleaching agents and the control group; however, the halogen group presented statistically lower DTS (p<0.05) than the LED group. For the MH test, the carbamide peroxide group presented statistically lower MH means (p<0.05) than the control groups, and there were no statistical differences among the light-curing units. Sixteen percent carbamide peroxide reduced the MH of the hybrid composite tested. The second generation LED presented a performance similar to or better than the halogen lamp for hardness and DTS, respectively. Repolishing of minifill hybrid composite is suggested, as the alteration caused after the contact with 16% carbamide peroxide was limited to the material surface. The second generation light-emitting diode is a good option for a curing light device when the polymerization initiator of composite resin is camphorquinone.

Phototherapy in anti‐aging and its photobiologic basics: a new approach to skin rejuvenation

Intrinsic aging and photoaging of the face are constantly ongoing, and eventually result in the typical "aged" face, with visible lines and wrinkles at rest, a variety of dyschromia and a tired, dull and lax epidermis over poorly organized elastotic dermal architecture characterized by many interfibrillary spaces. Both ablative and nonablative resurfacing have been reported as solutions, the former providing excellent results, but a long patient downtime, and the latter giving little or no downtime, but less-than-ideal results. In ablative resurfacing, the epidermis is removed and replaced with a "new" epidermis, whereas in the nonablative approach the epidermis is spared through some form of cooling. In both approaches, however, the goal is to create controlled amounts of thermal damage in the dermis to stimulate the wound healing process, thus generating a tighter, better organized, "younger" dermal matrix. A better approach might be to apply prevention, rather than the cure, and to treat subjects in their very early 20s, before even fine lines have begun to appear. This "photoanti-aging" approach could be achieved with the use of very low incident levels of photon energy to stimulate the skin cells, both epidermal and dermal, at cell-specific wavelengths based on the photobiological findings of the literature over the past two decades or so, in order to increase their resistance to the effects of chronological and photoaging. Lasers and IPL systems could be used, but are extremely expensive and therapist-intensive. A new generation of light-emitting diodes (LEDs) has appeared as the result of a spin-off from the US NASA Space Medicine Program, which are much more powerful than the previous generation with quasimonochromatic outputs. These LEDs can offer target specificity to achieve photobiomodulated enhanced action potentials of the skin cells, in particular mast cells, macrophages, endotheliocytes, and fibroblasts, plus increases in local blood and lymphatic flow, in a noninvasive, athermal manner. New phototherapeutic LED-based systems have appeared to meet the need for a less-expensive but clinically useful light source to enable photoantiaging as a reality in clinical practice. Some studies proving the efficacy of LED therapy have already appeared, and based on their results LED therapy represents a potential new approach to prevention in anti-aging, so that further studies are warranted to prove its efficacy.

Low-picomolar limits of detection using high-power light-emitting diodes for fluorescence

Fluorescence detectors are ever more frequently being used with light-emitting diodes (LEDs) as the light source. Technological advances in the solid-state lighting industry have produced LEDs which are also suitable tools in analytical measurements. LEDs are now available which deliver 700 mW of radiometric power. While this greater light power can increase the fluorescence signal, it is not trivial to make proper use of this light. This new generation of LEDs has a large emitting area and a highly divergent beam. This presents a classic problem in optics where one must choose between either a small focused light spot, or high light collection efficiency. We have selected for light collection efficiency, which yields a light spot somewhat larger than the emitting area of the LED. This light is focused onto a flow cell. Increasing the detector cell internal diameter (i.d.) produces gains in (sensitivity)3. However, since the detector cell i.d. is smaller than the LED spot size, scattering of excitation light towards the detector remains a significant source of background signal. This can be minimized through the use of spectral filters and spatial filters in the form of pinholes. The detector produced a limit of detection (LOD) of 3 pM, which is roughly three orders of magnitude lower than other reports of LED-based fluorescence detectors. Furthermore, this LOD comes within a factor of six of much more expensive laser-based fluorescence systems. This detector has been used to monitor a separation from a gel filtration column of fluorescently labeled BSA from residual labeling reagent. The LOD of fluorescently labeled BSA is 25 pM.

How light source and product shade influence cure depth for a contemporary composite

Directly placed light activated resin based composite restorations are becoming increasingly popular for restoring cavities in posterior teeth. Marketing and patient as factors well as operator preference are behind this trend. Achieving adequate depth of cure is critical to the success of these restorations. Recently a number of second generation light emitting diode (LED) light activation units have been marketed and the manufacturer of one of these claims that it is capable of curing in half the time of its predecessor. This study tested that claim using a companion composite from the same manufacturer. The relationship between cure depth, shade changes on curing and opacity were also assessed. Under the limitations of the current investigation the results indicated that the second generation LED unit in question met the manufacturer's claim for halving cure time. Depths of cure approached those of a control halogen unit in half the 40 s radiation time of the latter. For the product tested depth of cure is strongly linked to material opacity.

ULTRASTRUCTURAL OBSERVATIONS OF HUMAN SKIN FOLLOWING IRRADIATION WITH VISIBLE RED LIGHT-EMITTING DIODES (LEDs): A PRELIMINARY IN VIVO REPORT

Ablative and nonablative skin rejuvenation procedures with lasers and intense pulsed light (IPL) systems have become very popular for photorejuvenating sun- and chronologically aged skin. Both procedures demand deposition of heat damage in the upper dermis. A new generation of light-emitting diodes (LEDs) with laser-like wavebands and phototherapeutically useful output powers are now reported to be successful for noninvasive athermal photorejuvenation of age-damaged skin. This study was designed to examine the ultrastructural changes induced by irradiation of human skin with visible red LED energy. Six adult male volunteers who satisfied all study criteria had the skin over their fibula irradiated once per week for 8 weeks with a visible red LED-based system at an irradiance of 105 mW/cm 2 , 15 min/session and a radiant flux of 94 J/cm 2 . Skin punch biopsies taken from each subject after the second and eighth treatment sessions were routinely prepared for transmission electron microscopy (TEM) and were examined under an electron microscope. After the 2nd session, the skin showed normal undamaged tissue with slight interstitial edema and vimentin filaments notable in fibroblasts. After the 8th session, the number of fibroblasts in the dermis had increased with numerous vimentin filaments in their cytoplasm, and a mild inflammatory infiltration could be seen. The ultrastructure of human skin after 8 LED phototherapy sessions showed no damage-related abnormalities. Mild athermallymediated inflammation was seen together with an increased fibroblast count and enhanced metabolism, which could be related to the enhanced synthesis of collagen and which in facial skin would probably result in an improved skin appearance.

The Lily Pond

The Lily Pond (Fig. 18 and Color Plate A No. 1) was prepared as an installation for Burning Man 2002 and, as with many creative works, it began life as something much different than what it eventually evolved into. Born of my desire to create a large-scale interactive environment, the Pond was originally conceived as a large array of electronic devices that would respond both visually and audibly to people passing near them. Function quickly gave way to form upon my realization that there was no reason these devices could not be sculptural as well as functional. Prior experience with botanical sculpture led me and my colleagues to the idea of each device becoming a plant; from there it was a short leap to the concept of the lily pond. The Lily Pond came to consist of nearly 300 lily pads, mounted 22 inches above the ground and covering an area of roughly 3,500 square ft. Each pad is actually a green circuit board, fabricated in the shape of a lily pad and home to the various electronic circuits that give life to the Pond. The pads are arrayed in a hexagonal grid on 4-ft centers. This arrangement allows one to walk amongst the pads, experiencing the illusion that one is wading into a knee-deep pond. The illusion of wading is greatly enhanced at night, when each lily pad projects a diffuse blue glow onto the ground beneath it. As one walks among the pads, they individually modulate their light levels, in effect simulating the movement of ripples on water. These ripples of light propagate out into the pond, where they collide and combine with other ripples. Wanting to expand the concept beyond the basic idea of a pond full of interactive lily pads, we looked to the flora and fauna of a real pond. In the natural environment, objects of inspiration are plentiful; we found abundant material to draw from. We selected a few elements that interested us for inclusion in the first incarnation of the Pond. Roughly two-dozen of the lily pads sport lotus blossoms made of lampworked glass and stainless steel. These flowers are lit from within and slowly fade on and off and change colors. Seven dragonflies, in the form of wire-frame sculptures, inhabit the Pond. The wings of the dragonflies are illuminated with fiber optics and are animated in a way that suggests rapid motion. The glass eyes of the dragonflies are also lit with a soft light that slowly fades on and off. A pond would not be complete without fish, and The Lily Pond is home to several varieties. Five full-sized ceramic koi lurk beneath the surface, their eyes and barbles glowing gently in the night. There are four different schools of trout, also ceramic, as well as a dozen carp, made of kiln-cast glass. The trout and the carp are illuminated with miniature colored spotlights hidden beneath the lily pads. The shore of the Pond is made of several large steel sculptures suggestive of the reeds, ferns and grass that accompany a real pond. These sturdy sculptures also serve as a buffer zone between the vast unknown exterior world and the quiet, contemplative space of the Pond. Breathing life, motion and light into the Pond requires the collision of several different technologies. The light sources used to illuminate the ground are some of the latest generation of light-emitting diodes (LEDs), which are rapidly becoming the most efficient light sources available. In order to produce the rippling water effect, the lily pads “talk” to one another, using infrared technology similar to that found in television remote controls. The ripple effect itself is based upon a relatively new branch of science known as cellular automata. And finally, each lily pad contains its own power source that is recharged every day by a set of photovoltaic solar cells. Thus the entire Pond is wireless and self-sustaining, powered by the sun. The Lily Pond represents a variety of techniques, technologies, materials and creative visions. Collaborators include the Sunbrothers (lotus blossoms and solar cells), Kathleen Fernald (ceramic fish), Michael Christian (shore sculpture), Lee Kobus (glass fish) and Jay Kravitz (glass fish).

Second generation LEDs for the polymerization of oral biomaterials

Objectives. New blue, so called second generation light emitting diodes (LEDs) are now available with a high optical power output. These LEDs will potentially find widespread application in commercially available light curing units (LCUs). This study, therefore, investigated the curing performance of a prototype LCU containing one high power LED and a conventional halogen LCU (Polofil). Methods. The performances of the LCUs were evaluated by measuring the Knoop hardness and depth of cure of the composites. Three dental composites were selected (Z100, Admira and Revolcin Flow) in a light (A2) and a dark shade (A3.5 or A4), respectively, and were polymerized for 40 s each. Results. The LED prototype (irradiance=901 mW/cm 2) achieved a statistically significantly greater ( p<0.05) depth of cure than the halogen LCU (irradiance=860 mW/cm 2) for all composites. Generally, there was no statistically significant difference in Knoop hardness on the top and bottom of a 2 mm thick disk for the composites Z100 and Admira if polymerized with the LED prototype or halogen LCU. The composite Revolcin Flow, however, showed in general a statistically significant lower Knoop hardness if polymerized with the LED LCU. Significance. The present study shows that second generation LEDs have the potential to replace halogen LCUs if the composites are selected carefully. Furthermore, this study confirmed that the depth of cure test does not discriminate between LCU's performance for composites containing co-initiators, but the Knoop hardness test does.