Tag Archives: science

non-visual effects of light

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.


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.

3D colour printer


An article in Stuff reveals what 3D Systems claims to be the world’s first continuous-tone full colour 3D plastic printer, called the ProJet 4500.The ProJet 4500 offers full-colour parts with colours that are able to blend into each other with gradient transitions.

eyes change colour?


I didn’t realise how sophisticated reindeers are. It turns out they have two layers of fur to help them keep warm, are able to shrink the pads on their hooves to give then better grip, and can detect ultraviolet light which enables them too see in very dim light. And it also turns out that their eyes can change colour in winter so that their vision is more sensitive. Reindeers, like cats, have a reflective layer behind the retina (which is the inside of the eye ball where all the light-sensitive cells are) that helps them to see in dim light. This is why, if you see a cat at night, you might see the eyes shining; you are seeing light being reflected back at you from the cat’s tapetum lucidum (which is the technical term for the layer behind the retina). The light that shines back in most animals with this layer is golden but in reindeer it apparently shifts to blue in the winter. The shift to blue allows more light to be scattered and improves the vision of the animal.

The full paper can be read in the Proceedings of the Royal Society.

Where is colour mixing?

Imagine that we have three projection lamps at the back of a hall – one has a red filter and so produces a beam of red light, and the other two use filters to produce green and blue beams. We project these onto a white screen and get three circles of light (one, red, one green and one blue). We then move the angles of the projectors so that the circles of light overlap. We get something that looks rather like this:


Where the red and green light overlap we get yellow. We get magenta and cyan for the other two binary mixtures. So,

red + green = yellow

red + blue = magenta

green + blue = cyan

This is called additive colour mixing as I am sure you know. And if we mix all three primaries we can achieve white (or other neutral colours). The primaries could be single wavelengths of light – so we could use a primary at, say, 700 nm (for the red) and one at 450 nm (blue) and one at 530 nm (green). So green light (530 nm) and red light (700 nm) additively mix together and generate yellow. When this happens what is being mixed and where does this mixing take place? Take a few moments to consider this before reading on.

Notice I said that they additively mix to generate yellow – I specifically avoided saying that they mix to generate yellow light. When I sat down with a couple of students last week and asked then what they though they said that the red and green light mixed together to create yellow light and when I pressed them, they went further to say that the yellow light was at about 575 nm.


If we measure the part of the screen that is yellow we would see that we have some light at 700 nm and some at 530 nm. The wavelengths are not mixed; they don’t mix together to generate some third wavelength of light such as 575 nm. So no physical mixing takes place other than – I suppose one could argue – that the red and green lights are mixed in the sense that they are spatially coincident. But that’s not really mixing, for me, and certainly doesn’t even begin to explain why we have the sensation of yellow when we look at these wavelengths together. It also makes me think that additive colour mixing, if it can be said to occur anywhere in particular, occurs in the eye. And I do mean eye, not brain.

Colour survey

personal care products-1
I am currently carrying out some research using an on-line questionnaire about colour choices by consumers in product design. It would really help me a lot if you would take the survey. It only takes about 1 minute to complete. The link is http://questionpro.com/t/AKSnxZP9ij. Please feel free to share this link.

In a few weeks when the survey is completed you can come back to this page and you can see more details about what we were doing, why we were doing it, and what we found.


Can colour save lives?

I have worked in colour for pretty much all my working life. Though it has led to a rewarding and stimulating career (with a little bit of success) and though my passion for colour has never waned, I do sometimes wonder if i could have put my life to something more useful. Not that colour is not useful, far from it, but what I mean is something that could save lives. For example, perhaps I could have become a researcher looking into a cure for cancer. Compared with research like that, doesn’t colour sometimes seem frivolous and secondary?

So my Friday morning today was just cheered up a little when I came across an article in the Grundig about how colour-changing technology could revolutionise the medical industry. Apparently, 1.3 million people die each year because of unsafe injections, making the humble injection the most dangerous clinical procedure in the world. Part of the problem is that syringes are sometimes accidentally reused without sterilisation.


In response to this serious issue, David Swann at the University of Huddersfield – just down the road from where I work – developed a “behaviour-changing syringe” that warns when the needle is unsafe. Once opened the syringe turns bright red within sixty seconds. It’s not even expense. Apparently a standard syringe costs 2.5 pence whereas the “behaviour-changing syringe” costs 2.65 pence.

See the original article here.

colour conference in UK


In July of this year the UK is hosting the 12th International Congress of the International Colour Association. We have received over 600 submissions from people who would like to present their work and so it looks as though we can have a very successful conference. If you have an interest in colour then this is the place to be this year – for further details visit http://aic2013.org/

aic_2013_logo_bringing_colour_to_life (1)



The 12th International Congress of the International Colour Association (AIC) is taking place in July next year in the UK. The deadline for submitting abstracts is 17th December 2012 so there is not much time. Please visit http://aic2013.org/ for further information about how to submit abstracts and about how to get involved generally. The Congress will be held in Gateshead which is on the opposite side of the river to Newcastle and will take place in the iconic Sage conference centre. Attending AIC is a great way to meet other people who share your interest in colour.

chemical additives

A few weeks ago I posted about the safety of food colours. My argument was that the issue is not whether food additives are natural or man-made (let’s even say chemical because that really sounds nasty – even though water is a chemical and we are made of chemicals). Rather, the issue is whether any additives are safe or not, since plenty of natural products are highly dangerous (even fatal) and the vast majority of man-made additives are perfectly safe. My good friend, Mark Bishop (Professor at Goldsmiths) commented that maybe people feel safer with natural additives because they have been around for longer and so we are more certain about whether they are safe or not. He may have a point – today it was revealed that 4-methylimidazole (which is added to Pepsi and Coca-Cola) is carcinogenic. Presumably this chemical was once thought to be safe.