Light-emitting diodes (LED) for domestic lighting: any risks for the eye?

Light-emitting diodes (LEDs) are taking an increasing place in the market of domestic lighting because they produce light with low energy consumption. In the EU, by 2016, no traditional incandescent light sources will be available and LEDs may become the major domestic light sources. Due to specific spectral and energetic characteristics of white LEDs as compared to other domestic light sources, some concerns have been raised regarding their safety for human health and particularly potential harmful risks for the eye. To conduct a health risk assessment on systems using LEDs, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES), a public body reporting to the French Ministers for ecology, for health and for employment, has organized a task group. This group consisted physicists, lighting and metrology specialists, retinal biologist and ophthalmologist who have worked together for a year. Part of this work has comprised the evaluation of group risks of different white LEDs commercialized on the French market, according to the standards and found that some of these lights belonged to the group risk 1 or 2. This paper gives a comprehensive analysis of the potential risks of white LEDs, taking into account pre-clinical knowledge as well as epidemiologic studies and reports the French Agency's recommendations to avoid potential retinal hazards.

Pin guidance of reconstruction plate contour: an expanded role of external fixation

This article presents a modification of intraoperative external fixation for mandibular reconstruction with free tissue flaps. This technique is indicated when preregistration of the reconstruction plate is not possible due to transmandibular tumor extension. Once standard external fixation has been carried out and prior to segmental mandibulectomy, additional pins are fixed to the connecting rod that delineate the mandibular contour in three-dimensional (3D) space. Following mandibulectomy, these pins allow accurate contouring of the reconstruction plate and improved restoration of mandibular contour, projection, and dental occlusion. A step-by-step description of the technique using models and intraoperative photos is presented. This method of mandibular reconstruction is a simple and time-effective alternative to intraoperative computer navigation and 3D modeling in select cases of oral carcinoma where tumor infiltration of the outer mandibular cortex precludes prebending of the reconstruction plates.

Katse tulevaan päin!

Pääkirjoitus

"Tulta päin - tulta päin" : näönseulonta Helsingin kaupungin pelastuslaitokselle

Palomiehen ammatti on arvostettu sen fyysisen ja psyykkisen vaativuuden vuoksi. Pitkät työvuorot ja äärimmäistä fyysistä suorituskykyä vaativat tehtävät asettavat rajoituksia ammatin harjoittajille. Työn vastuullisuus ja korkeat työssä onnistumisodotukset tekevät palomiehen työstä henkisesti hyvin raskasta. Siksi kyseisessä ammatissa vaaditaankin vankkaa työhön sitoutumista sekä korkeaa motivaatiota. Vaativat työolosuhteet nostavat myös työssä näkemisen arvoa, vaikka palomies-sairaankuljettajan ammattiin ei ole asetettu erityisiä näkövaatimuksia. Opinnäytetyössämme kartoitimme operatiivisissa tehtävissä työskentelevien palomies-sairaankuljettajien tämän hetkistä näkemisen tilannetta. Tutkimusaineistoa keräsimme näönseulonnalla sekä kyselylomakkeella, jossa kysyttiin palomiesten omia kokemuksia näkemisestään. Työ tehtiin yhteistyössä Helsingin kaupungin pelastuslaitoksen kanssa. Kvantitaviivisen opinnäytetyömme tutkimusjoukko koostui 50 palomies-sairaankuljettajasta. Näönseulonnalla ja kyselylomakkeilla saamamme tulokset analysoitiin SPSS-ohjelman avulla. Tutkimuksessa analysoimme palomiesten näkökykyä sekä vertailimme näönseulonnasta saatuja tuloksia palomiesten omakohtaisiin näkökokemuksiin. Tutkimustuloksista voidaan päätellä, että palomiesten näöntarkkuudet olivat yleisesti ottaen hyvät. Lähes kaikilla tutkituista palomiehistä myös kontrastiherkkyydet, stereonäkö ja värinäkö olivat normaalit. Suurin osa palomiehistä koki ongelmia lähityöskentelyssä, joka on yhteydessä tutkimusjoukon keski-ikään. Palomiesten omakohtaiset kokemukset näkemisestään korreloivat hyvin näönseulonnan tulosten kanssa. Hyvin harva käytti silmälaseja työtehtävissään, koska niiden käyttö koettiin yleisesti ongelmalliseksi työtehtävien aikana. Tutkimuksemme tulosten perusteella palomiesten työterveyshuollossa täytyisi ottaa paremmin huomioon ongelmat heidän näkemisessään.Heidän näköongelmiinsa tulisi etsiä erilaisia ratkaisuja erityisesti ikänäköisten ja piilolasien käyttäjien kannalta. Työterveyshoitajan olisi hyvä tehdä yhteistyötä optikon kanssa, jolloin ammattitaitojen yhdistyessä päästäisiin parhaisiin ratkaisuihin.

Readout schemes for low noise single-photon avalanche diodes fabricated in conventional HV-CMOS technologies

Three different pixels based on single-photon avalanche diodes for triggered applications, such as fluorescence lifetime measurements and high energy physics experiments, are presented. Each pixel consists of a 20µm x 100µm (width x length) single photon avalanche diode and a monolithically integrated readout circuit. The sensors are operated in the gated mode of acquisition to reduce the probability to detect noise counts interferring with real radiation events. Each pixel includes a different readout circuit that allows to use low reverse bias overvoltages. Experimental results demonstrate that the three pixels present a similar behaviour. The pixels get rid of afterpulses and present a reduced dark count probability by applying the gated operation. Noise figures are further improved by using low reverse bias overvoltages. The detectors exhibit an input dynamic range of 13.35 bits with short gated"on" periods of 10ns and a reverse bias overvoltage of 0.5V. The three pixels have been fabricated in a standard HV-CMOS process.

Optoelectronic studies in nanocrystalline silicon Schottky diodes obtained by Hot-Wire Chemical Vapour Deposition

The very usual columnar growth of nanocrystalline silicon leads to electronic transport anisotropies. Whereas electrical measurements with coplanar electrodes only provide information about the electronic transport parallel to the substrate, it is the transverse transport which determines the collection efficiency in thin film solar cells. Hence, Schottky diodes on transparent electrodes were obtained by hot-wire CVD in order to perform external quantum efficiency and surface photovoltage studies in sandwich configuration. These measurements allowed to calculate a transverse collection length, which must correlate with the photovoltaic performance of thin film solar cells. Furthermore, the density of charge trapped at localized states in the bandgap was estimated from the voltage dependence of the depletion capacitance of these rectifying contacts.

Retinal damage induced by commercial light emitting diodes (LEDs).

Spectra of "white LEDs" are characterized by an intense emission in the blue region of the visible spectrum, absent in daylight spectra. This blue component and the high intensity of emission are the main sources of concern about the health risks of LEDs with respect to their toxicity to the eye and the retina. The aim of our study was to elucidate the role of blue light from LEDs in retinal damage. Commercially available white LEDs and four different blue LEDs (507, 473, 467, and 449nm) were used for exposure experiments on Wistar rats. Immunohistochemical stain, transmission electron microscopy, and Western blot were used to exam the retinas. We evaluated LED-induced retinal cell damage by studying oxidative stress, stress response pathways, and the identification of cell death pathways. LED light caused a state of suffering of the retina with oxidative damage and retinal injury. We observed a loss of photoreceptors and the activation of caspase-independent apoptosis, necroptosis, and necrosis. A wavelength dependence of the effects was observed. Phototoxicity of LEDs on the retina is characterized by a strong damage of photoreceptors and by the induction of necrosis.

Mikael Agricolan teosten päin-partikkeli

Summary: The particle päin in the works of Mikael Agricola

Effects of the epitaxial layer thickness on the noise properties of Schottky barrier diodes

An analytical theory to describe the combined effects of the epitaxial layer thickness and the ohmic contact on the noise properties of Schottky barrier diodes is presented. The theory, which provides information on both the local and the global noise properties, takes into account the finite size of the epitaxial layer and the effects of the back ohmic contact, and applies to the whole range of applied bias. It is shown that by scaling down the epitaxial layer thickness, the current regime in which the noise temperature displays a shot-noise-like behavior increases at the cost of reducing the current range in which the thermal-noise-like behavior dominates. This improvement in noise temperature is limited by the effects of the ohmic contact, which appear for large currents. The theory is formulated on general trends, allowing its application to the noise analysis of other semiconductor devices operating under strongly inhomogeneous distributions of the electric field and charge concentrations.

Impedance field and noise of submicrometer n+ nn+ diodes: analytical approach

A theoretical model for the noise properties of n+nn+ diodes in the drift-diffusion framework is presented. In contrast with previous approaches, our model incorporates both the drift and diffusive parts of the current under inhomogeneous and hot-carrier conditions. Closed analytical expressions describing the transport and noise characteristics of submicrometer n+nn+ diodes, in which the diode base (n part) and the contacts (n+ parts) are coupled in a self-consistent way, are obtained

Effects of the epitaxial layer thickness on the noise properties of Schottky barrier diodes

An analytical theory to describe the combined effects of the epitaxial layer thickness and the ohmic contact on the noise properties of Schottky barrier diodes is presented. The theory, which provides information on both the local and the global noise properties, takes into account the finite size of the epitaxial layer and the effects of the back ohmic contact, and applies to the whole range of applied bias. It is shown that by scaling down the epitaxial layer thickness, the current regime in which the noise temperature displays a shot-noise-like behavior increases at the cost of reducing the current range in which the thermal-noise-like behavior dominates. This improvement in noise temperature is limited by the effects of the ohmic contact, which appear for large currents. The theory is formulated on general trends, allowing its application to the noise analysis of other semiconductor devices operating under strongly inhomogeneous distributions of the electric field and charge concentrations.