PHOTONICS WEST REPORT REVIEW


Getting LEDs into homes requires education, panellists say


combines a monolithically integrated graphene detector array on a CMOS readout integrated circuit. It covers the spectral range from 400nm to 1,800nm; the pixel size is 20 x 20µm, the frame rate 100fps, and it has a dynamic range of 80dB. The sensor operates well at room temperature. The company has also developed graphene- based bolometers for thermal imaging, which Dr Tapani Ryhänen, CEO of Emberion, noted had higher sensitivity than traditional bolometers. This means they give good performance without cooling, which could reduce the price of a thermal imaging system. Emberion’s bolometers exploit heat-


to-charge conversion using pyroelectric substrates coupled with charge detection using graphene field-effect transistors. They have a VGA array size, a spectral response of 3µm to 5µm and 7µm to 14µm, a video frame rate of 30Hz to 60Hz, and a noise equivalent temperature difference of 15mK to 30mK, uncooled. Koppens’ group has also investigated


graphene-CMOS integration for silicon photonics, where graphene photodetectors have been integrated with silicon waveguides. Broadband modulators have also been shown where the absorption can be tuned, and all of this is based on wafer-scale production processes. Graphene can also be layered on top of plastic, which makes it suitable as a detector for wearable devices. ICFO has demonstrated a graphene optical sensor on a rubber wrist band that measures heart rate without needing a light source. It uses light from the environment, so is very low power. EO


Educating consumers and retailers and labelling products more clearly will be necessary for improving the penetration of LED lighting into homes, speakers commented during a panel discussion on solid-state lighting at Photonics West. The speakers at the industry


event, which took place on 31 January, were responding to a member of the audience asking why many consumers still haven’t adopted LEDs in their homes, and why the quality of LED light can be poor and degrade over time. Clifton Stanley Lemon,


president of the San Francisco section of the Illuminating Engineering Society (IES), disagreed that LED light is of poor quality, stating that it has the potential to be far superior to light produced by incandescent bulbs or compact fluorescent lamps (CFLs). However, it can be difficult for consumers to shop for the right bulb at shops and differentiate between good and bad quality products. ‘LEDs are capable of being considerably better then incandescent in every respect,’ he said. ‘Of course I’m in the industry, but you can get a good quality $5 lightbulb – you have to look for them though. It is difficult for the average person. Even when I go to the store I struggle to see a CRI [colour rendering index] label on any of the bulbs, which tells you the


accuracy of the colour.’ Robert Steele, a solid-state lighting consultant, added that there are cheaply made, poor-quality LED products on the market, which consumers should be made aware of: ‘The retailers need to educate the customers,’ he said. Dima Simonian, colour scientist at Telelumen, said that the cost difference between the poor quality light sources and true LEDs with excellent light quality is not huge. ‘So, if people knew about the dramatic differences between low and high quality, they would pay a little bit more to get the better quality product,’ he said. Steele pointed out that it’s also important to provide guidance on colour temperature – either on the product label or to consumers directly – as this has a huge effect on the light’s appearance: ‘People will buy something that’s 5,000 kelvin, which will look really blue. So education is important.’ Aaron Smith, director of


technology at Finelite, agreed, and said that with the advent of new technology there is much more choice, which can confuse consumers. ‘With incandescent lighting there was always just one colour – it was that way for a very long time. Now, there is a plethora of choices, and the ability to pick the right light source becomes more complicated,’ he commented.


‘So, education is definitely needed – to help consumers with the scene, understand the differences between light sources, how the light will look and the effects of light in different situations.’ However, Steele added that


part of the transition to LEDs involves consumers getting used to the slight differences in how LEDs look compared to the traditional bulbs. ‘One problem is that even


though… you can buy an LED lightbulb with a colour temperature of 2,700 kelvin [the same as an incandescent bulb] the spectrum is different – you’re not replicating the spectrum of an incandescent source,’ he noted. ‘So, it will look a little different – part of it is just getting used to this new source.’ The lighting industry has


gone through a massive transition in the last five to six years, noted Steele, as the adoption of LED products in general lighting has grown from around zero to representing more than half of the sales of the $80 billion lighting market (a combination of lamps, bulbs and fixtures) last year. ‘If that penetration continues,


in the next four to five years we could see LED lighting representing almost 100 per cent of all general lighting around the world, bar a few specialised uses where legacy lighting may still play a role,’ he commented.


can count white blood cells in cerebrospinal fluid – which is how the infection is diagnosed – in an automated way.


Spinal meningitis is an acute inflammation of the membranes covering the brain and spinal cord, which can be fatal within 24 hours. Until now, early diagnosis of


Leti’s prototype with Pixcurve technology compared to a commercial reference: performance improves, while size, complexity and cost are reduced


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the infection required an operator using an optical microscope to manually count white blood cells in cerebrospinal fluid. As a result, meningitis cannot be diagnosed in emergencies or operating rooms, or during routine medical care in developing countries.


Leti’s lens-free, operator-free


technology requires fewer than 10 microlitres of cerebrospinal fluid to differentiate between white and red blood cells, and can give a reading almost in real time. The lens-free microscope was


tested on 200 patients at Marseille Timone Hospital in France to detect or confirm spinal meningitis. A blind lens-free microscopic analysis of 116 cerebrospinal fluid specimens, including six cases of microbiologically confirmed infectious meningitis, yielded 100 per cent sensitivity and 79 per cent specificity.


March 2018 Electro Optics 15


Leti CEA


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