Shedding light on LEDs

Conversing with a computer-generated face playing the part of the "voices" experienced by patients with schizophrenia can suppress the problem within hours in some individuals, new research has revealed...

A small trial of 16 patients at University College London by a team led by Julian Leff, who invented the techique, achieved in three participants complete cessation of the distracting auditory hallucinations - usually one or more voices making disparaging and distracting comments - that had been plaguing the patients for years. And even in those participants for whom the technique did not completely suppress their auditory hallucinations, almost all showed improvements in their symptoms and wellbeing more generally.

The approach involves first asking the patient to use a computer to design an "avatar" that best represents, for them, the face of the source of the most intrusive voice that they hear in their head. They also use computer software to generate a voice that most closely resembles the voice they experience. The therapist then sits in another room and can make the avatar "speak" to the patient in a convincing way, using lip-syncing software.

Initially the avatar behaves in a critical and confrontational way, but the patients are urged to be confrontational in return. Slowly, over 6 one-hour sessions, the therapist alters the way the avatar engages with the patient, switching from being highly negative to being positive, collaborative and encouraging.

The result is that the patient gains confidence and feels that the threat posed by the voice is reduced so they can legitimately "tell it where to go". In three of the 16 patients initially enrolled, the voices were arrested completely. Followed up at 3 months, the benefits largely remained.

The researchers speculate that the approach works because, although schizophrenic patients generally lack insight into the authenticity of the voices they can hear, because they have created the avatar themselves, they are not at risk from it so they need not be fearful of trying out control strategies to make it cease.

Most schizophrenics are too fearful of the voices they hear to risk disobeying them. But the avatar gives them the mental fortitude to do this and, perhaps, fools their own brain into suppressing the real voice alongside the one they can see on the screen. The team have now secured substantial grant funding to evaluate and refine the technique on a further 142 patients over the next 18 months.

Plants entombed in glacial ice for more than 400 years have been successfully resuscitated by scientists in Canada.

The bryophytes, forms of moss including liverworts, have been revealed in the Canadian Arctic by the melting of the Ellesmere Island "Teardrop Glacier," which is retreating at between 3 and 4 metres per year.

Catherine La Farge, a researcher at the University of Alberta, noticed on a visit to the area that, as the ice receded, a matt of dark plant material was being revealed, some of which appeared, a short while later, to be green and showing signs of regrowth. She and her colleagues collected samples of the plants and placed them in culture media in the laboratory.

Other samples were used for carbon dating, which confirmed that the material was 400 and 600 years old and was probably buried in ice during the Little Ice Age in medieval times. Of 24 specimens put up for culture, 7 grew, regenerating viable plants.

That these plants can remain viable for so long under freezing conditions reflects their ancient origins, over 470 million years ago. They are very simple organisms which, unlike their more recently evolved counterparts, lack a vessel system for transporting water in the plant.

As such, they have little control over water movement through and to their tissues, so they have evolved to be highly tolerant of dessication, shutting down the activity of their cells when water is scarce. At the same time, all of their cells are capable of regenerating a new plant, behaving like a totipotent stem cell seen in animals.

Together, these traits make bryophytes highly successful pioneer species that can colonise harsh terrain. And now we also know, thanks to this work published this week in PNAS, that they probably also make a hitherto unrecognised contribution to the re-establishment of plant ecosystems in polar regions as glaciers retreat...

This week marks the 60th anniversary of the first complete ascent of Mount Everest by Edmund Hillary and Tensing Norgay in 1953. But few people know that had it not been for the failure of one of two competing designs of breathing equipment - a completely different pair of climbers could have made it to the top first.

Here's your Quickfire Science from Hannah Critchlow and Kate Lamble.

The summit of Mount Everest is 8848 meters or 29,029 feet high, that's higher than some aeroplanes fly. At this altitude there is only a third of the oxygen available at sea level.

At higher altitudes, the same percentage of oxygen is found in the air, but the drop in overall atmospheric pressure means there is in effect, less air overall.

Above 8000 meters is the so-called 'death zone' where the amount of oxygen is not sufficient to sustain human life, even at rest.

Before the first ascent of Everest mountaineers typically used an open breathing system to deliver extra oxygen and make the climb easier. This system works by adding oxygen to the air the climber is breathing in, and their exhaled breath is released around them - like in scuba diving.

However one British Scientist Tom Bourdillon, thought that the system was wasteful as we absorb less than a fifth of the oxygen we breathe in. In an open system this oxygen we breathe out is lost.

In 1952 he developed a closed 'rebreathing' system which recycled the expelled climbers breath and passed it over soda lime to remove the carbon dioxide.

More oxygen was then added to the air, multiplying the amount the climber could absorb before it was breathed in again.

On the 1953 Everest expedition several groups of climbers made an attempt on the summit simultaneously. This included Tom Bourdillon and his climbing partner Charles Evans as well as Edmund Hillary and Tenzing Norgay.

Using the new re-breathing system, Bourdillon and Evans ascended Everest at record rate - climbing 1,500ft in 90 minutes. The same stretch took Hillary and Tenzing more than two hours.

Eventually they came within 90m of the summit of Everest but a problem with their new oxygen system forced them to turn back. No-ones sure what made the equipment fail but it could have been an air leak, or frozen valve

Three days later Edmund Hillary and Tenzing Norgay reached the summit using their open breathing system and became household names.

Since Bourdillon and Evans failed in their ascent, open systems have continued to be favoured for mountaineering but scientists are now using Bourdillon's design to develop medical devices which could help patients with obstructive lung diseases.

Now there's long been a search for energy efficient lighting which could replace the wasteful incandescent bulbs which governments around the world have started programmes to phase out.

However, the current most commonly available energy efficient bulbs, Compact Fluorescents, take time after being switched on to warm up and are widely seen as producing a harsh blue colour of light.

Now though breakthroughs in LED technology are offering a cheap alternative. We're joined in the studio by Colin Humphries Director of Research at the Department of Materials Science and Metallurgy at the University of Cambridge who's been working on bringing LED technology to the wider market

Dave - What actually is an LED?

Colin - An LED is a solid which when you pass a tiny electric current through it, it emits brilliant light and I brought along a children's toy here and this is a pig. And with one finger, I could just press this lever on this pig and you get bright light emitted from this pig, and if I stop pressing, I've actually put enough energy into this that bright light continues to shine now. So, they're extremely energy efficient.

Dave - So, far better than the conventional light bulb where you're just heating up a piece of wire and I guess wasting a lot of energy.

Colin - Far better than conventional lighting. If I may add just a slight correction, a conventional light bulb is actually only 5% efficient, 95% comes out of heat, right? A compact fluorescent lamp, these so-called low energy light bulbs, they're about 20% efficient. So, they're 80% inefficient, even these so-called low energy light bulbs.

Dave - So, what sort of efficiencies can you get out of LEDs?

Colin - LEDs at the moment, you can buy now a 30% efficient, so there are already something like 6 times efficient as an old fashioned light bulb. But in the laboratory, we have them at 60% efficient and they'll be coming on to the market in the next few years.

Dave - So, that really is an improvement.

Colin - They'll be the most efficient source of lighting available, yes.

Dave - But one problem I guess with LEDs is if you want to actually go and buy them they're quite expensive. What's the problem with that and why are they so expensive?

Colin - So, they're really expensive because in order to get a sufficient light out, you have to have about 8 or 10 LEDs in a sort of light bulb shape. So, this is a Philips bulb which I got in John Lewis and it costs 13 pounds and it's a 48-watt equivalent bulb. Not many people will spend 13 pounds even though over its lifetime, you'll save lots of money in electricity, so you'll save over all. But the initial outlay is too expensive for people.

These are expensive because they're something like 8 or 10 LEDs. Each LED costs about 1 or 2 pounds. This is because they're grown on sapphire or silicon carbide wafers, and a wafer is - think of an ice cream wafer or a cheese wafer. So, a sapphire wafer, you actually grow a big piece of sapphire artifically, you slice it up into wafers. Sapphire is really expensive and silicon carbide is expensive. Silicon itself is really cheap. And so, you save a lot of money by growing on silicon.

Dave - What you're actually growing on the silicon or the silicon carbide?

Colin - We're depositing a material called gallium nitride which does not exist in nature. So, it's a man-made material and then the material which actually emits the light is something called indium gallium nitride. So, it's three different elements put together - indium, gallium and nitrogen and those elements are in very thin layers called quantum wells and it's those layers which emit the brilliant light.

Dave -  How do you get the colour of the LED? Are they naturally white?

Colin - A really good question. So, the light is emitted by the indium gallium nitride and if we have 15% indium in this indium gallium nitride, you get blue light. If you have 25% indium, you get green light. If you have 80% of indium, you get red light. It's like cookery in a sense. You just change the composition, change the mixture and you get different lights. And in fact, I've got here some LEDs I brought along and if you push these buttons, you'll see all sorts of different colours.

And then to get white light, we take blue light and this is another demonstration I brought along. This is in fact, one of the first gallium nitride on silicon LEDs we made, it's not incredibly efficient in this demo. We've improved efficiency but it's still pretty bright. And so, this is blue light that you take.

Dave - So, that's quite a deep blue light.

Colin - It is, that's right and if you place what's called a phosphor on top, that converts the blue light to white light and a phosphor is a material where you put in high energy photons which are blue and you get out low energy photons which in this case are yellow. And the phosphor is very thin so the blue light shines through this yellow phosphor to give white light.

Dave - Is this an efficient process converting blue light into the other colours.

Colin - Well, that's a really good question because you lose energy in the phosphor and also, in going from a high energy photon to a low energy photon, you use energy. So, the next generation after this, you'll get rid of phosphor altogether and you'll make white light by having red, green and blue LEDs individual ones. And you'll combine them together to make white light and you might have a little control like the control on a television set which actually can control the colour rendering of this white light. So, in the morning when you wake up, you might have bluish white light, you might have a romantic dinner with reddish white light. But you'd be able to control the colour of the light you get.

Dave - This might sound like a stupid question, but why aren't you doing that already?

Colin - We are not doing that already because for reasons we don't understand, this is where the research comes in, the efficiency of green LEDs is less than blue or red. We don't know why, so that's a science problem to solve, but if you can solve that problem then we'll have very efficient white lighting from red, green and blue.

Dave - So at the moment when you buy an LED, it's based on a sapphire wafer which is an expensive thing, and you're replacing that with silicon, why isn't that easy?

Colin - All the commercial LEDs you can buy at the moment. They're grown on sapphire wafers or silicon carbide wafers, and they're both very expensive. So, we had the idea of growing on silicon wafers and that's much more difficult to do scientifically because when you heat up silicon, it expands at a very different rate from when you heat up gallium nitride. And we grow these LEDs at 1,000 degrees centigrade. It's very, very hot. So, when you cool down, the LEDs just crack because of this. And so, what we do, we deliberately had to introduce layers which introduce compression into the system and it matches the tension you'll get when it cools, so it doesn't crack. And the other thing is you get lots of defects when you grow on silicon, about 10 times more than when you grow on sapphire. And so, we introduce special clever techniques to actually minimise and reduce the defect density.

Dave - So, how much is growing it on silicon going to reduce the price of an LED?

Colin -  Well, silicon is really cheap. So, a 6-inch diameter silicon wafer costs about 20 pounds. A 6-inch diameter sapphire wafer will cost about 500 pounds. So, you know, it's much more than 10 times cheaper and then if you use silicon, you can go through a 6-inch processing line and all the fabrication, high yield and everything we associate with sillicon chips, you can get that on these LEDs.

One criticism of the current generation of energy saving lightbulbs is their colour, but it's not just that people find blue light a bit harsh, scientists are also discovering that blue light can affect your sleep cycle, especially if you're reading before you go to sleep.  

Chris spoke to Russell Foster, Professor of circadian Neuroscience at Oxford University to find out how lighting might be affecting our lives.

Russell - Well, the eye of course detects light in two very different ways. The eye is used to construct an image of our world and of course, that's vision and we've understood that for centuries. But of course, there's another function of the eye and that's to detect overall levels of brightness in the environment and you use this to regulate physiology ss diverse as the body clock, levels of alertness. And what's turned out to be really remarkable is that there are different sorts of receptors - the classical receptors, the rods and the cones are building the image of the world and then there's another light sensor called a photosensitive retinal ganglion cell which is measuring brightness and firing information directly into those areas of the brain which regulate these non-visual responses to light.

Chris -  So, we've evolved as humans to wake up in the morning and go to bed when it gets dark. So, what influence and what impacts are there on our health of having artificial light?

Russell -  Well, when Edison invented the light bulb and it became widely used in the 20^th century, it allowed us to essentially invade the night. And it's been estimated that even people who aren't doing things like shift work are probably sleeping 1 ½ to 2 hours less every night because of the use of artificial light. And overall, the levels of sleep we're getting as a society and as individuals is vanishingly small compared to a pre-industrial age. So, what artificial light has done is compress a really rather expanded sleep period into perhaps as little as 6 hours, 6 ½ hours for most people.

Chris - What about the type of light though because Edison's light bulb put out a certain range of wavelengths that were effectively a nice comfortable daylight resembling glow? We're now making light bulbs that actually, I'm just looking at some, that are powered by LEDs that produce quite a harsh blue colour. So, does the type of light potentially have an impact?

Russell - Yes, it does. These photosensitive ganglion cells are pure brightness detectors. And interestingly enough, they're most sensitive to the blue wavelengths of light. So, these blue enriched LEDs will very much stimulate those cells that we use to regulate our body clocks, our levels of alertness, and indeed, our pupil size.

Chris - And of course, one of the places where we're seeing a lot of these LEDs being used is in computer screens which if you believe what Facebook and Twitter tell us, the last thing, something like half of young people in Britain and the probably the rest of the world do before they go to bed is to check what's on their Facebook page or their Twitter account. So, we must be getting quite high exposure to this very blue-dominated light late at night.

Russell - Yes, it's absolutely fascinating because of course, there is this biological predisposition for teenagers to go to bed late and get up late. But it's enormously exaggerated by the sorts of things you're talking about. Checking one's Facebook and going on and exposing one's self to these screens. Now, it's not particularly bright and the earliest screens probably weren't bright enough to shift the body clock which needs quite a bit of light. But they certainly would've been bright enough to raise levels of alertness and therefore, delay night time sleep. So, these screens are sort of exaggerating this biological predisposition for teenagers to go to bed late and get up late.

Chris - What about in the workplace or just in the home, more generally, as we adopt bluer dominated lighting? Is that always a bad thing? Is it not good in the morning to have that because it might make me feel a bit perkier?

Russell - I think that's exactly the right thing and it's the intelligent use of these light sources that could be incredibly powerful. So, what you need is bright morning light exposure to set the body clock to local time and that will be terrific. So, exposure in the morning to these bright light sources will be very good and in addition, they will increase levels of alertness in the workplace. The downside would be having bright light exposure at the other end of the day when you're trying to get to sleep and one of the most extraordinary things is, I've seen some of these devices being incorporated into bathroom mirrors. Now, the last thing many of us do of course is clean our teeth in front of a bright mirror before we go to bed and of course, that hugely increases our levels of alertness and delays our sleep. So, it's not just in sort of computer screen type devices, but it's in many applications where inappropriate light exposure is not necessarily going to be good for us.

Chris - Do you think then that now, we can make things like LEDs that can put out different wavelengths, we could have timed LEDs that will be very blue dominated in the morning to get us going. Then as the day goes on, they can be tuned so that people do feel more relaxed as the day goes on. And then as you go to bed at night, you're seeing much more red dominated light and this doesn't have this enlivening effect when you're trying to go to sleep.

Russell - I think that's a very exciting application. I mean, the intelligent use of these devices could be incredibly powerful in fine-tuning both our visual biology, but also, the biology of the sleep-wake cycle.

Chris - Is there actually any evidence that it is having ill-effects though because everything you said so far, I don't disagree with, but it's all based on - well, this is going to make people feel more awake or it's going to put us out of step with what our body clock should be doing, but is there any evidence that's actually bad?

Russell - We have a few studies that have emerged which have looked at the impact of iPads and devices like that on supressing melatonin. And of course, melatonin suppression is often used as a surrogate measure for the impact of light on the body clock. And these devices were shown to supress melatonin and so, yes, we do have some real biology that the non-image forming photoreceptor systems, the non-visual systems are being affected by these devices.