Light and Colour: in perfect harmony

Could I write something about the relationship between Light and Colour?
Probably . . .

Light and Colour – hanging out together

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Let’s talk about the relationship between light and colour – and what comes first?

There is no chicken or egg here, there is only the chicken AND the egg. Without the chicken, there is no egg; without the egg there is no chicken.

Without light there is no colour; without colour there can be no light. The two states are intrinsically wrapped into one another.

How does it work?

Let’s take Light first. We have to start with a source of illumination. It may be a candle flame on a restaurant table; it may be a star 93,000,000 miles away warming our backs on a sunny day. That essential shift from mass (candle wick) into energy (heat) into visual light (incandescence) is the starting point for everything that we see.

Photons flow out from our primary light source and will travel until they hit another surface; then the story changes.

Everything that we see is a light source in its own right, because we can only see what the eye can register, and the eye registers photons. Some of the photons flying off the surface of an object enter the eye, hit the retina –  and we recognise the object as a flower pot on a table, or the dog lying in the hall, waiting for us to trip over it.

So the photon from the primary source hits the object, which becomes the secondary sources, creating photons that come into the eye.

And it gets more complex. If the secondary photons come from an object that is an intense colour – red, say – then those secondary photons will then create tertiary photons that will contain an echo of the secondary source when, in turn, they are ‘reflected’ off a white ceiling and the entire room will appear to be tinted red. Magic!

White light contains ‘all the colours of the rainbow,’ as originally demonstrated by Isaac Newton with his prism  – just to upset Percy Shelley a 150 years later, who described this act of scientific vandalism as ‘unweaving the rainbow; clipping an Angel’s wings’ .

If you remove parts of the rainbow – let’s call it the spectrum from hereon – then the light colour is changed. It’s called subtractive colour mixing. When we hold a sheet of red filter gel, what we actually have is a selective light barrier that stops all light that’s not at the red end of the spectrum.

You can go the other way and create coloured light from two different light colours. If you shine a red light at a white wall, the wall will turn a shade of red/pink. But if you add a green light on top of that, the wall will become yellow, because red and green are primary light colours. Mix then together and you get yellow.

Which means that is time to talk about pigment, because everyone knows that red and green make a mucky brown. All objects that we can see have a colour created by a pigment. We think that we know what the colour of a given pigment is. We don’t.

All we know is the colour of pigment under given light conditions. If you stray away from those given conditions, the pigment will appear different. This is a very complex idea and requires acceptance of a theory of everything is only relative to everything else and not free-existing within the universe.

How do we experience this in everyday life? We need to start back with our white light. Let me introduce you to the Black Body Radiator, or The Planckian Curve, to give it its posh name.

I’ve always preferred the down and dirty definition, because it starts with a cast iron cannonball. Let’s assume, for all intents and purposes, that our cannonball is black when at room temperature. As we apply heat to it, it eventually starts to turn red; then orange; then yellow; then WHITE; and then blue (assuming that it hasn’t melted and run all over the floor first).

The heat that we add can be measured, so that every degree of heat can be translated into a light colour. This is the colour temperature of the light source. White light generally varies from around 2000K (degrees Kelvin) to 10000K – in other words, from a yellow-white to a blue-white. If you want to see that in nature, look outside. The white light of daylight is up at the top end of the scale. Direct sunlight is around 5000K.

Light is not constant – and neither is colour

As the colour of the light varies, so does the colour of the clothes that we wear and the cars that we drive, all affected by the spectrum of the light that falls upon it.

There is the story of the little black dress . . . or was it very dark blue? The truth is, that is was both. The more blue in white light (from, say, daylight), the bluer the dress appeared. As the blue part of the spectrum fades away towards evening (at an evening soirée, perhaps), the dress becomes black. It is both very dark blue and black. Two dresses for the price of one – depending on your light.

By the way, take the black cocktail dress into a brightly-lit fast food joint and you’ll likely find it’s gone back to dark blue!

And when we add artificial light into the light+colour mix, things get even more complicated.

The closest real-life demonstration of the hot cannonball is inside the traditional tungsten lamp. All that’s happening in there is a length of wire (the filament) having an electrical voltage attached to it. The wire has a resistance which means that it heats up to the point of incandescence, to 2700K at full voltage. If you dim it down – by reducing the voltage – the light becomes yellow. This is most natural of artificial lights. Unfortunately, it’s also very inefficient so we can no longer afford to use it to illuminate our buildings.

We now use energy-efficient LED lamps (there are still other sources, such as fluorescent available, but the LED is the most commonly available source at the moment).

If you could take an LED chip apart you’ll find that the WHITE LED is actually blue. The WHITE colour is created by layers of phosphor that get applied to the blue chip. So the white light is a constructed light. There is nothing natural about it.

A lot of work is being done to bring the LED spectrum closer to that of daylight/sunlight, with some excellent results, but no LED can be assumed to be that good unless you know for certain. Most of the time, we assume that an unknown LED lamp is a BAD thing.

Where does this leave us?

Firstly, there are no absolutes – except that one. Everything that we experience is relative to something else in the environment – and that includes our own internal physical and psychological landscapes.

Remember this: the human eye/brain combo is:

  • VERY good at detecting movement – that’s a hangover from being stalked by sabre-toothed tigers
  • PRETTY good at seeing differences in colour – again, a defensive mechanism for noticing the difference the strips of a plant and the stripes of something that wants to eat us
  • RUBBISH at knowing how bright things are – we can’t tell whether we’re sitting in 500 Lux or 1000 Lux; 50 Lux or 100 Lux; 5000 Lux or 10000Lux. It’s not that important to us, after all. So long as we can see to do what we’re doing, that’s all that matters. If the brain took note of every light shift we’d probably go crazy.

When we deliberately put light and colour together there are some things we need to do.

ONE: If you’re doing any kind of colour matching, then recreate a test environment where those colours can be viewed under EXACTLY the lighting that’s to be used in the project..

TWO: Don’t assume that a colour reference will always appear the same regardless of the material that its applied to. There are fabrics that exhibit a thing called metamerism

It means that the colour that the fabric shows is dependent on the light source being used. A practical example of this was when a distraught interior designer came to me with two office chairs; a meeting room chair and a secretarial chair. Both chairs had the same fabric colour, apparently . . . except that they didn’t.

Seen under the lighting in the design studio, the blue looked the same; under the office lights (and by now several hundred of these chairs had been purchased), the meeting chair was behaving itself but the secretarial chair had turned into an intense electric blue – not a good look.

THREE: Don’t forget the light that you have little or no control over. Natural light does have an impact and can alter the way that we see things .

Changing Light (and Coour) during the day

One final note: this isn’t really the way that we see the world. Our brain has a fine cataloguing system that means we recognise objects by our familiarity with them. That blue car sitting outside will still be ‘blue’ even if its sitting under a mono-chromatic orange sodium street-light (which means the car will actually, and most certainly, be BROWN). But our cataloguing system says, that brown car over there is a really nice blue.

Unfamiliar objects don’t fare as well. A lovely little test is to walk into a plain room where all the surface are, say, red. Is it a red-painted room lit wit white light – or is it a white-painted room, lit wit red light. Whose to know? Only those people who set up the room in the first place.

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I hope that this introduction to Light and Colour is helpful to you. I’ve added links to Wikipedia for some of the technical terms. If any other esoteric light references have crept in, you might find a definition in The Light Review’s Glossary of Lighting Terms.

Books that are on my bookshelf on and around this subject that may be of interest to you:

  • Colour and Culture, John Gage: pub. Thames and Hudson
  • Ways of Seeing, John Berger: pub. Penguin
  • Colour and Vision, Steve Parker: pub. Natural History Museum
  • Catching the Light, Arthur Zajonc: pub. OUP
  • Light Fantastic, Peter Mason: pub. Penguin
  • Light. Color and Environment, Faber Birren: pub. Schiffer
  • The Language of Light, Rebecca Weir and Allyson Coates: pub. Artifice
  • The Little Book of Colour, Karen Haller: pub. Penguin

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