Tag Archives: light

Why are things coloured?

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Things are coloured because we have visual systems. In other words, without us – or some similar sentient being – there would be no colour.

“By convention there is sweetness, by convention bitterness, by convention color, in reality only atoms and the void.”, Democritus, 460-370 BCE.

If we eliminated all living beings from the universe there would be no colour, no sound, no smell. All that would remain would be physical stimuli.

I really believe this. But it doesn’t mean that colour doesn’t exist. It’s like saying that just because they are things that we experience – things that our brains produce – then pain and love don’t exist. Of course pain and love exist. But they don’t exist in the absence of sentient beings and the same can be said for colour. And all of our perceptions of course.

But this video – below – is not about that. It is about how everyday objects such as paints, plastics, textiles, prints etc. interact with light. Why do some objects absorb short wavelengths and others absorb long wavelengths.

For most objects it is all about dyes and pigments. Please watch the video below to hear more about this. And don’t forget to click like if it was worth your time.

Light and Sleep

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There was an interesting article in The Guardian today about a new blood test that can detect whether someone is sleep deprived. The idea is to use it to prosecute drivers involved in accidents who have had less than 5 hours sleep. According to the article driving after less than 5 hours sleep is as dangerous as driving after drinking alcohol. Experts are divided on the ethics of this.

This was particularly interesting for me for two reasons. Firstly, because this time last week I was on a flight from Manchester to LHR, en route to Texas where I took part in a couple of panel discussions about colour psychology having gone to sleep at 11:30pm the night before and left the house at 3:30am after fitful sleep for less than four hours. During the 1.5 hour drive from Leeds to Manchester in the early hours I had felt completely awake; however, I wonder whether I would be able to make this journey in a few years if the legislation is introduced.

But secondly, because my own research is concerned with the effect of light sleep and the devastating effects that lack of sleep can have on our health and wellbeing. A discussion about this topic actually came up during the Texas trip. I would encourage everyone to listen to Matt Walker’s superb TED talk – Sleep is your super power. We now know that light plays a crucial role in maintaining a healthy sleep schedule. Healthy sleep is entrained by exposure to bright light in the few hours after waking and to lack of exposure to light in the hours before going to bed. There is debate about the relatively importance of the light being blue. The light-sensitive cells in the retina that are implicated in sending signals to the hypothalamus in the brain (from where the release of hormones is controlled) are maximally sensitive to light at about 480nm but there is some evidence that longer wavelengths of light could also influence alertness (in other words, the cones may also be involved). Here is one of my own papers on this topic:

Lin J & Westland, 2020. Effect of long-wavelength light on electroencephalogram and subjective alertness, Lighting Research and Technology, 52 (6), 763-774.

There is already growing research into the use of light and light-related products to help us to sleep better. As public awareness of this issue grows it is inevitable that interest in to this topic will increase. Perhaps such products could be used to mitigate the effects of poor sleep in situations such as the one I was in last week.

See my related posts

colour helps you sleep
non-visual effects of light

is there such a thing as visible light?

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I would argue that there is no such thing as visible light – or at least that the term visible light is a meaningless one.

Light is part of the electromagnetic spectrum which is describes electromagnetic radiation by its wavelength. An electromagnetic wave has both electric and magnetic field components. What is really very interesting is that depending upon the wavelength of the field the electromagnetic radiation has very different properties and we give it a different name.

electromagnetic-spectrum

When the wavelength is very long, the radiation is radio waves or micro waves. When the wavelength is very short, the radiation is x-rays or gamma rays. There is a narrow range of wavelengths (from about 360 nm to about 780 nm – a nm is 0.000000001 of a metre) to which our eyes are sensitive. Because we can literally see this radiation we call it light. I still find it amazing that light, x-rays, radio waves, and microwaves are all essentially the same thing (electromagnetic radiation) with just a change in the wavelength!! However, my point for today is that light is radiation that is visible – to talk about visible light would be bizarre since by its very definition light is visible. Technically, visible light is a pleonasm; pleonasm is a word derived from the Greek word “pleon” meaning excessive. Other examples of pleonasms – easily confused with oxymora – include the phrases end result and invited guests.