Category Archives: nature

non-visual effects of light

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Most people know that the ear system has two functions: hearing and balance. It is less well known that the visual system also has two functions. The first is seeing. The second is a set of non-visual functions including circadian rhythm. Mechanisms are being discovered that are particularly sensitive to blue light. So short-wavelength, or blue, light inhibits melatonin which is a chemical that makes you drowsy. So looking at bright lights late at night, especially blue ones, can contribute to a poor night’s sleep. So put your smart tablet away now and go to sleep!

In all seriousness though, I knew there was a reason why I do not like watching Chelsea on Match of the Day.

colour

Studying these functional effects of colour and how they can be used in design is a major theme of the research I lead at the University of Leeds in the School of Design. If you have interest in these areas please contact me.

colour helps you sleep

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Light in our natural environment tends to be bluer first thing in the morning and redder at dusk.

Researchers from the University of Manchester looked at the change in light around dawn and dusk to analyse whether colour could be used to determine time of day. They constructed an artificial sky beneath which they placed mice and they then measured the body temperature of the mice for several days and their body temperature was recorded. The highest body temperatures occurred just after night fell when the sky turned a darker blue – indicating that their body clock was working optimally. When just the brightness of the sky was changed, with no change in the colour, the mice became more active before dusk, demonstrating that their body clock wasn’t properly aligned to the day night cycle.

According to Dr Timothy Brown: “This is the first time that we’ve been able to test the theory that colour affects the body clock in mammals. It has always been very hard to separate the change in colour to the change in brightness but using new experimental tools and a psychophysics approach we were successful. What’s exciting about our research is that the same findings can be applied to humans. So in theory colour could be used to manipulate our clock, which could be useful for shift workers or travellers wanting to minimise jet lag.”

What colour is the sky on mars?

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mars_originalmars_red

The cameras never lies. Or does it? Recently I had to take a photo for a medical case and before submitting it I had to sign to say that the photo had not been modified. I did this – but it was ridiculous of course. Many people have this idea that the cameras faithfully captures what the scene looks like and that, unless we intentionally manipulate the images (in photoshop, for example), then we have captured the truth. Nothing could be further from the truth – as the recent image of #TheDress showed.

The top photo above was taken and released by NASA in 1976 and shows a Martian landscape. The sky is blue. However, at the time, Carl Sagan said “Despite the impression on these images, the sky is not blue…The sky is in fact pink.”

You see the original image had not been colour corrected. Colour correction is a process that takes place on most cameras these days without the user being aware of it but in 1976 was not automatic. The process can compensate for the spectral sensitivities of the camera sensors (which may differ from one camera to another) or for the colour of the light source. The second picture (above) shows the colour-corrected image. Some people are now arguing, however, that the amount of colour correction applied by NASA is wrong and that the sky should not be as red as it appears on the second photograph. For the full story including some other nice images of Mars see here.

black plants can save the world

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leaves
About three years ago I posted about the question of why leaves are green. In this I postulated as to why chlorophyll (the green stuff in leaves) should be green; after all, this means that it only absorbing some of the wavelengths in the visible spectrum. In fact, I argued that it would be better if plants were black, absorbing all of the wavelengths in the visible spectrum. Now, someone on co.design is suggesting just that – that green plants absorb only about 2% of the possible energy and that scientists are thinking of turning them black. Presumably this would save the world because plants would be more efficient at converting harmful greenhouse gasses into oxygen. There’s catch though, apparently. If you make the plants black they get too hot and overheat resulting in cell damage. Actually, I also suggested this might be the case in my original article in 2011. Looks like black plants won’t save the world. They won’t even save themselves.

There’s nothing wrong with black carrots though – see here.

Structural colours

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butterfly

Most colours around result from light being absorbed (electronic transitions) and scattered by dyes and/or pigments. However, there was an interesting article in The Guardian today about structural colour. Structural colour is quite common in nature; it occurs when light is scattered because of a regularity in packing or structure; the wavelength of the light that is most strongly scattered is determined by the repeat distance of this packing, which has to be comparable to the wavelength of the light.

high blood pressure affects colour vision

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colourblind

Drinking alcohol not only affects your speech and balance. It can also affect your colour vision. Not just alcohol. Various drugs (some contraceptives and analgesics, for example) make you less good at discriminating between colours. And there are a load of medical conditions that also affect your colour vision including MS and diabetes. In fact, often a deterioration in colour vision can be one of the first indications of a problem. This is why it is a good idea, from a health perspective, to have your vision checked by a qualified professional on a regular basis.

Now some research from Japan suggests that deterioration in colour vision may be a predictor of hypertension – a condition in which the arteries have persistently elevated blood pressure. The study looked at 872 men aged between 20 and 60. They found that, when other factors were taken into account, as blood pressure values rose, the odds of having impaired colour vision increased as well.

For further information see here.

why do we value gold?

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gold

Could we have developed currency around elements other than gold and silver? Why couldn’t we have coins made out of platinum, for example?

Interesting article today on the BBC website interviewing Professor Sella (University Collage London) about why, of the 118 elements of the periodic table, it is gold (alongside silver) that we value and use for currency.

According to Prof Sella there are reasons to dismiss all the elements apart from gold and silver. For example, you couldn’t use elements that are gas (such as neon) or liquid (mercury) as currency because it would be impractical to carry them around. Several others (such as arsenic and the other liquid, bromine) are poisonous and so could not be practically used. The alkaline metals (those on the left-hand side of the periodic table) are not stable enough (they react with too many other elements). And, of course, say no more about the radioactive elements. Some of the so-called rare earths (such as cerium) could be used but they tend to be even more rare that gold and are actually quite difficult to distinguish from each other.

periodic-table

Prof Sella also postulates reasons for dismissing the 40 transition and post-transition elements such as copper, lead, iron and aluminium. Many are hard to smelt (needing temperatures as high as 1000 deg C) such as titanium and zirconium or hard to extract such as aluminium. Iron is easier to extract and smelt but rusts too easily. Iron is also too abundant.

Prof Sella lists the 8 noble metals (platinum, palladium, rhodium, iridium, osmium and ruthenium, gold and silver) as contenders. However, with the exception of silver and gold they are too rare and have other problems (platinum is hard to extract and has a very high melting point for example). So this leaves gold and silver. The choice of these metals is not arbitrary. It turns out that they have exactly the right properties that we need. They are stable, chemically uninteresting, rare (but not too rare), safe, relatively easy to extract, solid at room temperature and with a reasonably low melting temperature.

The article also explains why gold is golden in colour.

I like my carrots black

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carrot

On Christmas day of 2009 I posted about the colour of carrots.

I had been watching a Royal Institution Christmas Lecture by Prof Sue Hartley about carrots and why they are orange. She spoke about selective breeding by the Dutch (the first naturally occurring carrots were purple – from Afghanistan – and were later cultivated to be orange). In seeking to find more about this I found myself on the website of the British Carrot Museum. It is seriously worth a visit even if your interest in carrots is tangential.

I was reminded of this today when I came across an article in The Economic Times (India) which reported that the Punjab Agriculture University has developed its first black colour carrot variety (known as ‘punjab black beauty’) which has been recommended for general cultivation in the state. The black carrot is the best alternative to tackle the malnutrition problems of the country because it is overloaded with beneficial anti-oxidants and nutrients. The punjab black beauty is is rich in anthocyanins, phenols, flavonols ß-carotene, calcium, iron, and zinc.

I am also reminded, of course, of the words of the great late Uncle Monty (aka Richard Griffiths): “I think the carrot infinitely more fascinating than the geranium. The carrot has mystery. Flowers are essentially tarts. Prostitutes for the bees. There is a certain je ne sais quoi – oh, so very special – about a firm, young carrot”.

Eat red, eat less

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Eat_red2

It used to be thought that blue was an appetite suppressant because blue foods are rare and sometimes poisonous. But I have always doubted this and wrote about it near three years ago on this blog. And then nearly two years ago I posted about research from the University of Basel (Switzerland) and the University of Mannheim (Germany) in which it was shown that participants drank less from a red cup than a blue cup and ate less snack food from a red plate than from a blue plate. In other words, the opposite of what was commonly believed. Today I read in CNN about work by Nicola Bruno, a cognitive psychologist from the University of Parma, about his research to measure how much food or hand cream people used when presented on plates of different colours (red, white or blue). The food and hand cream was available to be used freely whilst participants took part in a survey. People ate less food and used less hand cream when either was presented on a red plate. However, the authors note that in their experiment the participants were unaware of the experiment – so it is not so straight forward to extrapolate and conclude that if you buy red plates for home you would eat less. Because then you would be conscious of the idea and it might not work. On the other hand, it might!!

It was nice for me to hear this story and it reminded me of when Nicola came to visit me (when I worked at Keele University) and we published a paper together. That was in about 2000 and I don’t think I have seen him since. Sometimes it isn’t a small world. But it was nice to come across him again anyway.