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Monday, 27-Jan-2014 08:22 Email | Share | | Bookmark
0fweek: 3D images at 1 photon per pixel



Lidar rangefinders, which are common tools in surveying and in autonomous-vehicle control, among other applications, gauge depth by emitting short bursts of laser light and measuring the time it takes for reflected photons to arrive back and be detected.



In this week’s issue of the journal Science, researchers from MIT’s Research Laboratory of Electronics (RLE) describe a new lidar-like system that can gauge depth when only a single photon is detected from each location. Since a conventional lidar system would require about 100 times as many photons to make depth estimates of similar accuracy under comparable conditions, the new system could yield substantial savings in energy and time — which are at a premium in autonomous vehicles trying to avoid collisions.



The system can also use the same reflected photons to produce images of a quality that a conventional imaging system would require 900 times as much light to match — and it works much more reliably than lidar in bright sunlight, when ambient light can yield misleading readings. All the hardware it requires can already be found in commercial lidar systems; the new system just deploys that hardware in a manner more in tune with the physics of low light-level imaging and natural scenes.



Count the photons



As Ahmed Kirmani, a graduate student in MIT’s Department of Electrical Engineering and Computer Science and lead author on the new paper, explains, the very idea of forming an image with only a single photon detected at each pixel location is counterintuitive. “The way a camera senses images is through different numbers of detected photons at different pixels,” Kirmani says. “Darker regions would have fewer photons, and therefore accumulate less charge in the detector, while brighter regions would reflect more light and lead to more detected photons and more charge accumulation.”



In a conventional lidar system, the laser fires pulses of light toward a sequence of discrete positions, which collectively form a grid; each location in the grid corresponds to a pixel in the final image. The technique, known as raster scanning, is how old cathode-ray-tube televisions produced images, illuminating one phosphor dot on the screen at a time.



The laser will generally fire a large number of times at each grid position, until it gets consistent enough measurements between the times at which pulses of light are emitted and reflected photons are detected that it can rule out the misleading signals produced by stray photons. The MIT researchers’ system, by contrast, fires repeated bursts of light from each position in the grid only until it detects a single reflected photon; then it moves on to the next position.



A highly reflective surface — one that would show up as light rather than dark in a conventional image — should yield a detected photon after fewer bursts than a less-reflective surface would. So the MIT researchers’ system produces an initial, provisional map of the scene based simply on the number of times the laser has to fire to get a photon back.



Filtering out noise



The photon registered by the detector could, however, be a stray photodetection generated by background light. Fortunately, the false readings produced by such ambient light can be characterized statistically; they follow a pattern known in signal processing as “Poisson noise.”



Simply filtering out noise according to the Poisson statistics would produce an image that would probably be intelligible to a human observer. But the MIT researchers’ system does something cleverer: It guides the filtering process by assuming that adjacent pixels will, more often than not, have similar reflective properties and will occur at approximately the same depth. That assumption enables the system to filter out noise in a more principled way.



Kirmani developed the computational imager together with his advisor, Vivek Goyal, a research scientist in RLE, and other members of Goyal’s Signal Transformation and Information Representation Group. Researchers in the Optical and Quantum Communications Group, which is led by Jeffrey Shapiro, the Julius A. Stratton Professor of Electrical Engineering, and senior research scientist Franco Wong, ran the experiments reported in the Science paper, which contrasted the new system’s performance with that of a conventional lidar system.



“They’ve used a very clever set of information-theoretic techniques to extract a lot of information out of just a few photons, which is really quite incredible, and they’ve been able to do it in the presence of a lot of background noise, which is also impressive,” says John Howell, a professor of physics at the University of Rochester. “Another thing that’s really fascinating is that they’re also getting intensity information out of a single photon, which almost doesn’t make sense.”



Howell believes that the technique could be broadly applicable. “There are many situations in which you are light-starved,” he says. “That could mean that you have a light source that’s weak, or it could be that you’re interrogating a biological sample, and too much light could damage it. Our eyes are a very good example of this, but other biological systems are the same. There could also be remote-sensing applications where you may want to look at something, but you don’t want to give away that you’re illuminating that area.”


Friday, 3-Jan-2014 09:29 Email | Share | | Bookmark
LCD driver IC brisk sales to continue in 2014

Major Taiwan-based LCD driver IC players, including Novatek Microelectronics, Himax Technologies and Orise Technology, are set to enjoy continued sales growth in 2014 thanks to orders from China-based smartphone vendors, according to industry sources.



Players which can offer LCD driver ICs supporting higher display resolutions such as qHD, HD720 and Full HD, will gain a boost as China-based smartphone vendors are upgrading display panels used in their high-end models, instead of previous mainstream WVGA displays, indicated the sources.



Novatek, Himax and Orise have landed more orders for high-end driver ICs recently as these three firms all boast mature production lines for driver ICs supporting HD and above displays, the sources noted.



Shipments of LCD driver ICs supporting higher display resolutions, including HD and Full HD, currently account for 20% of Novatek's total driver IC shipments, said the sources, noting that Novatek is also able to supply IC parts supporting WQHD (2,560 by 1,440 pixels) displays.



However, keen competition in the segment will continue to press down the prices of HD and qHD driver ICs in 2014, commented the sources.




Display news


China's smartphone market changed the display ecosystem
Korean and Taiwanese display makers are paying attention to the Chinese smartphone market, as BOE sold more small and medium-sized panels in the Chinese market than Korean companies last year.




LG Display vows 4K panel counterattack
A big reason for plummeting prices on the latest generation of TVs is competition from China and Taiwan, aided by low-cost displays. One big supplier has plans to fight back.


Friday, 3-Jan-2014 09:23 Email | Share | | Bookmark
How to Replace a Halogen LED (light-emitting diode) bulbs

In an effort to reduce both their lighting and household cooling expenses, many homeowners have begun replacing their halogen light bulbs with cooler-burning, energy efficient LED (light-emitting diode) bulbs. The major obstacle to a straight one-for-one replacement scheme is that LED bulbs and halogen bulbs often have different dimensions and diameters. Finding a replacement bulb in the correct size and base configuration is more than half the battle in swapping an LED for a halogen bulb.



Instructions

1. Remove the halogen bulb you wish to replace from its fixture or lamp. Note its wattage and light output--usually measured in lumens or candela (candle power).

2.Visit any retailer selling LED bulbs with your old halogen in hand. Explain that you intend to replace your existing halogen bulb with a compatible LED bulb with the same type of base. Request assurances that if you buy a bulb that won't fit in your fixture, you can return it for a refund or exchange.

3. Examine the LED bulbs to find a suitable replacement. Pay particular attention to the base and shape of the LED. If possible, remove it from the packaging and compare it side-by-side with your halogen bulb. As an example, a medium or standard-base halogen bulb should be matched to an LED with the same base type. This also applies to intermediate, candelabra and mini-candelabra bases.


4. Match the light output of new LED bulb to the halogen bulb it is replacing. For instance, a 20-watt halogen bulb may put out from 200 to 300 lumens, LED lights marketed as replacements for a 20-watt halogen may only put out between 100 and 200 lumens, according to the study "Performance of Halogen Incandescent MR16 Lamps and their LED Replacements," conducted by the Pacific Research Laboratory for the U.S. Department of Energy in 2008. Light-output equivalency is usually marked on the packaging.



5. Install the LED into your existing lighting fixture or lamp. If it fits, you're finished. If it does not, return it to the retailer for a refund or exchange it for another LED which does fit.


Friday, 20-Dec-2013 03:07 Email | Share | | Bookmark
bright future for LED, if technology can deliver


Swapping out traditional incandescent light bulbs for light-emitting diodes (LEDs) has long been recognized as one of the single biggest energy conservation steps the world can take. And the LED industry continues to work to make that transition easier, especially by making the devices less expensive.



The reason for the interest in LEDs is simple: they are more energy-efficient, as much as 10 times more than traditional incandescent bulbs. With lighting accounting for half of all electricity used by industry, and a quarter of that used by homes, the savings that would result from an LED conversion are dramatic.



Governments all over the world are helping speed up the process by banning incandescent bulbs altogether. The EU started phasing them out in 2009; in the United States, the manufacture of 60-watt incandescent bulbs, the most common, will be prohibited starting next year.



While LED manufacturers have made remarkable advances in recent years, engineers say the technology still has to overcome several fundamental challenges before it becomes the universally accepted system its boosters hope it to be.



The most significant of these is cost, where great progress has already been made. In the U.S., 60-watt LEDs can now be had for as little as ten dollars, a third of the price of bulbs just a few years ago. While significantly more than the one- or two-dollar price tag of incandescent bulbs, LEDs last far longer; up to 50 times as long, by some studies.



IMS Research, the Englewood, Colorado-based market research firm, says that the current annual value of the LED market is now $85 billion, a figure it predicts will grow to $120 billion by 2017, but then shrink back down to $105 billion by 2020. That late-decade market dip, though, does not signify a decline in demand for LEDs, but instead, reflects the fact that their prices will continue to drop and their replacement rates, owing to their longevity, will be much lower than for incandescents.



Among the other goals that LED manufacturers are still looking to accomplish are to eliminate the annoying phenomenon of flicker. While incandescent lights continue to glow evenly as power levels fluctuate, LED lights are much more sensitive to even tiny changes in their electrical supply, something which occurs commonly in household electrical systems. The resulting flicker bothered some early users of LEDs, and companies are working on designing it away.



The industry also wants LED bulbs to have better color temperature when they are dimmed. While LED lights are easily dimmable—unlike compact fluorescent lamps, (CFLs) which have also been in contention to be a replacement for incandescent— they put out a dull, harsh white light at lower wattages. This is quite different than the gentle warm glow that most users want in a room when the lights are dimmed, a problem the industry is trying to rectify.



There’s one other dimming-related goal. Early LEDs required special new dimmer switches, adding to their expense. The ideal for LED manufacturers is to make them compatible with all existing dimmers, and they are making progress towards that goal.



Compact fluorescents never came close to reaching their potential, largely because consumers never took to them; they took too long to reach full brightness, among other complaints. So far, LEDs are escaping the worst of the criticisms leveled at CFLs. They are a bright spot on the global energy picture, one the industry wants to make even brighter.


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