Lighting : LIGHTING-June-July-2017
40 LIGHTING MAGAZINE | June/July 2017 June/July 2017 | LIGHTING MAGAZINE 41 A new imaging technique that modifies confocal adaptive optics scanning light ophthalmoscopy (AOSLO) could revolutionise how eye health and disease are assessed. Using their new, non-invasive imaging technique, researchers at the University of Rochester Medical Center are able to make out individual cells at the back of the eye that are implicated in vision loss in diseases like glaucoma. They hope their new technique will prevent vision loss via earlier diagnosis and treatment for these diseases. Through experimentation, the researchers were able to distinguish individual retinal ganglion cells (RGCs), which bear most of the responsibility of relaying visual information to the brain. There has been a longstanding interest in imaging RGCs because their death causes vision loss in glaucoma, the second leading cause of acquired blindness worldwide. Despite great efforts, no one has successfully captured images of individual RGCs, in part because they are nearly perfectly transparent. Instead of imaging RGCs directly, glaucoma is currently diagnosed by assessing the thickness of the nerve fibres projecting from the RGCs to the brain. By the time retinal nerve fibre thickness has changed detectably, a patient may have lost 100,000 RGCs or more. There are only 1.2 million RGCs in the whole eye, so a loss of 100,000 is significant. The sooner the loss can be caught, the better our chances of halting disease and preventing vision loss. Researchers collected multiple images, varying the size and location of the detector they used to gather light scattered out of the retina for each image, and then combined those images. The technique, called multi-offset detection, was performed in animals as well as volunteers with normal vision and patients with age-related macular degeneration. Not only did this technique allow the group to visualise individual RGCs, but structures within the cells, like nuclei, could also be distinguished in animals. The hope is that if they can achieve that level of resolution in humans, they will be able to assess glaucoma before the retinal nerve fibre thins – and even before any RGCs die – by detecting size and structure changes in RGC cell bodies. While RGCs were the main focus of the investigations, they are just one type of cell that can be imaged using this new technique. Using their multi-offset technique in age-related macular IMAGING TECHNIQUE VISUALISES INDIVIDUAL RETINAL GANGLION CELLS A view of the retina: the optic disc (blind spot with optic nerve and blood vessels) on the right and the macula (responsible for high quality colour vision), roughly in the centre of the image. The Drusen are the yellow spots in and around the macula. degeneration patients, the team was able to assess the health of cones near Drusen (small, bright structures seen in the retina and in the optic disc) and in areas where the retina had been damaged. This technique offers the opportunity to evaluate many cell classes that have previously remained inaccessible to imaging in the living eye – not only RGCs, but potentially other translucent cell classes and cellular structures. More studies will be needed to improve the robustness of the technique and ensure the results are reproducible before it can be widely used in a clinic. – Biophotonics DEVELOPING AN ECOFRIENDLY DEEP-UV LAMP Using atomically controlled thin monolayers of gallium nitride (GaN) and aluminium nitride (AlN) as active regions, a research group has shown the ability to produce deep-UV emission with an LED between 232 and 270nm wavelengths. Currently, most deep-UV lamps are mercury-based and are bulky and inefficient. A deep-UV LED would provide a smaller, more eco-friendly alternative to a mercury lamp. Researchers at Cornell University and the University of Notre Dame, achieved electrically injected deep UV emission using monolayer thin GaN/AlN quantum structures as active regions; and tuned the emission wavelength by controlling the thickness of ultrathin GaN layers using plasma assisted molecular beam epitaxy. In experiments the team achieved single peaked emission spectra with narrow full width at half maximum for three different LEDs operating at 232, 246 and 270nm. The team believes that 232nm (5.34 eV) is the shortest electroluminescence emission wavelength reported so far using GaN as the light emitting material. One of the challenges with UV LEDs is efficiency, which is measured in terms of the proportion of electrons passing through the device that are injected into the active region; the proportion of electrons in the active region that produce photons; and the proportion of photons generated in the active region that can be extracted for practical use. In the deep-UV range, efficiency can be impaired in all three areas. If each of the three components has 50 percent efficiency, then the overall efficiency is 0.5 x 0.5 x 0.5 = 0.125 or 12% efficiency. By using GaN instead of conventional aluminium gallium nitride (AlGaN), the researchers were able to increase the proportion of electrons that produced photons, as well as the proportion of electrons that could be extracted for actual use. They increased the proportion of electrons injected into the active region by using a polarisation- induced doping scheme for both the negative (electron) and positive (hole) carrier regions. Deep-UV LEDs are used to destroy harmful organisms including viruses, bacteria, mould and dust mites, as well as in food preservation and counterfeit currency detection. – Photonics.com NEW BOOK CELEBRATING LRC’S 30 YEARS’ COLLABORATIONS As the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute nears its 30th anniversary, it has become apparent that the collaborations between LRC researchers and the leading manufacturers and government agencies that comprise the LRC Partners and Alliances have made a significant impact on the world around us – not only in advancing lighting technologies and applications, but in the way people think about light. To celebrate these powerful collaborations, the LRC has published a book featuring 20 projects that have shaped our world – from enabling the broad adoption of solid-state lighting, to improving human health and wellbeing, to training the next generation of leaders in lighting. “The most effective collaborations occur when academia, industry and government serve as partners for transformation,” said LRC Director Mark Rea. “This has been the central philosophy for the LRC since its inception, exemplified by the collection of selected accomplishments in our book.” The LRC Partners are Current, powered by GE; the New York State Energy Research & Development Authority (NYSERDA); OSRAM; Philips Lighting; and the Swedish Energy Agency. LRC Alliance members include: z The Alliance for Solid-State Illumination Systems and Technologies (ASSIST): Acuity Brands Lighting; Amerlux; BAE Systems; Bridgelux; Crystal IS; Current, powered by GE; Dow Corning; Eaton; Federal Aviation Administration; Finelite; Hubbell Lighting; Lumens; Lumileds; NYSERDA; Noveda Technologies; OSRAM; OSRAM Opto Semiconductors; Philips Lighting; Seoul Semiconductor; and the US Environmental Protection Agency. z The Light & Health Alliance: Acuity Brands; Cree; Current, powered by GE; Ketra; OSRAM; Philips Lighting; and USAI Lighting. z The Lighting Energy Alliance: Efficiency Vermont, Energize Connecticut, and National Grid. z The Transportation Lighting Alliance: Audi, Automotive Lighting, Hella, OSRAM, Lumileds, and Varroc Lighting. At the end of the book, the LRC thanks the nearly 400 manufacturers, government agencies, and other organisations who have sponsored research at the LRC over the past 29 years. An electronic version of the book is available at http://www.lrc.rpi.edu/resources/book/LRCBook.html. VALE PRANAB BANDYOPADHYAY 01.12.1935 (Rangpur, Bangladesh) – 22.03.2017 (Kolkata) It was with a deep sense of loss that we at Indian Society of Lighting Engineers (ISLE) received the news of the passing of Pranab Kumar Bandyopadhyay (universally known as PKB). He was a founding member and a long term office bearer of the Society. With Hari Mamak, he was active in achieving Indian participation in international lighting organisations, such as the CIE and Lux Pacifica.
LIGHTING August-September 2017