The Perception of Colour
Article by Gemma Hutchings | Date Published 8th August 2024
Perceiving Pigment Through Human Vision
The intricate collaboration between the human eye and brain translates light into the spectrum of colours we perceive. Within the eye, light receptors convey messages to the brain, orchestrating the production of the colours we see.
The perception of colour on the skin is influenced by various factors, including the properties of light, the way light interacts with the skin, and the concept of refraction.
Sir Isaac Newton astutely noted that colour is not an intrinsic quality of objects; instead, it is a result of how the surface of an object reflects certain colours while absorbing others.
In our perception, only the reflected colours manifest, creating the vibrant palette that shapes our visual experience.
For example red is not ‘in’ an apple. The surface of the apple reflects the wavelengths we see as red and absorbs all the rest. An object appears white when it reflects all wavelengths and black when it absorbs them all.
Table of Content
Black and white are often seen as simple colours, but their appearance and properties reveal a lot about how light interacts with materials. Understanding these colours from the perspective of light absorption can be fascinating and enlightening. Let's delve into the science behind why black and white appear the way they do.
Light is a form of electromagnetic radiation, and visible light is the portion of the electromagnetic spectrum that human eyes can see. This light consists of different wavelengths, each corresponding to a different colour. When light strikes an object, it can be absorbed, reflected, or transmitted.
Black: The Absence of Light
Absorption: Black objects appear black because they absorb all wavelengths of visible light and reflect none. When light hits a black surface, the energy from the light is absorbed by the material, converting it into heat. This is why black surfaces can become very hot under sunlight.
No Reflection: Since no light is reflected back to our eyes, the object appears black. In essence, black is the result of the complete absorption of light without any reflection.
White: The Reflection of All Light
Reflection: White objects, on the other hand, reflect all wavelengths of visible light equally. When light strikes a white surface, it bounces off in all directions, and all the different wavelengths (colours) combine to appear white to our eyes.
No Absorption: Unlike black surfaces, white surfaces do not absorb significant amounts of light energy. Instead, they reflect almost all of it, which is why white objects stay cooler in sunlight compared to black objects.
Red, green and blue are the additive primary colours of the colour spectrum. By varying the amount of red, green and blue light, all of the colours in the visible spectrum can be produced.
Refraction is the bending of light as it passes from one medium to another with different densities. This concept can best be observed by placing a spoon in a glass of water.
Observation:
When you place a spoon in a glass of water, you notice that the spoon appears bent or broken at the point where it enters the water. The part of the spoon submerged in water seems to be at a different angle compared to the part that is in the air.
Explanation:
Light Behaviour: As light travels from air (a less dense medium) into water (a more dense medium), it slows down and bends towards the normal line (an imaginary line perpendicular to the surface of the water).
Refraction: This bending of light is known as refraction. The light rays coming from the spoon underwater bend when they exit the water and enter the air, making the spoon appear at a different position or angle than it actually is.
Result:
The bending or displacement is due to the change in speed of light as it moves between the two mediums. This is why the spoon appears bent at the water's surface.
The perception of colour on the skin is influenced by various factors, including the properties of light, the way light interacts with the skin, and the phenomenon of refraction. Let's explore how these elements work together to alter the colours we see on the skin.
The Role of Light
Source of Light:
The type of light source (natural sunlight, fluorescent light, LED light, etc.) can affect how colours appear on the skin. Different light sources emit light at various wavelengths and intensities, influencing the perception of colour.
Wavelengths and Skin Pigments:
Skin contains various pigments such as melanin, haemoglobin, and carotene, which absorb and reflect different wavelengths of light. Melanin, for example, absorbs more light and reflects less, making the skin appear darker.
Refraction is the bending of light as it passes through substances of different densities. In the context of skin, light undergoes refraction as it travels through the multiple layers of the skin.
Skin Layers and Refraction:
The skin is composed of several layers, including the epidermis (outer layer) and the dermis (inner layer). These layers have different densities and optical properties.
When light enters the skin, it passes through the epidermis and dermis, bending (refracting) as it moves from one layer to another. This bending of light alters its path and changes how we perceive colour.
Scattering and Absorption
Scattering: Light scattering occurs when light is deflected in multiple directions as it passes through the skin. Scattering can diffuse colours, making them appear less intense or slightly different than their true colour.
Absorption: Different pigments in the skin absorb specific wavelengths of light. For example, melanin absorbs a significant amount of UV and visible light, affecting the perceived darkness of the skin.
Impact on Perceived Colour:
As light refracts and scatters within the skin, the colours we perceive can change. For instance, tattoos may look different depending on the angle of the light and the thickness of the skin over the tattooed area.
Similarly, areas of the skin with more melanin or blood vessels might appear darker or redder due to the absorption and refraction of light.
Named after the 19th-century physicist John Tyndall, refers to the scattering of light by particles in a colloid or in a very fine suspension. This effect is responsible for the way we perceive certain colors, especially in translucent or semi-transparent materials like the human skin.
When light hits the skin, it penetrates the surface and interacts with the various layers beneath. The Tyndall Effect plays a significant role here:
Scattering of Light
Blue light is scattered more than red light because it has a shorter wavelength. As light passes through the skin, the shorter blue wavelengths scatter more, which can make veins appear blue even though blood is red.
Depth of Penetration:
Light that penetrates deeper into the skin before being scattered can change in color because it interacts with different types of tissue and pigments. Hemoglobin, the pigment in blood, absorbs light differently than melanin, the pigment in the skin, which leads to variations in color perception.
In essence, the Tyndall Effect causes a shift in the apparent color of objects beneath the surface of the skin due to the differential scattering of light. This is why veins, for example, often appear blue even though the blood within them is red. The light that reaches our eyes after passing through the skin and blood has been scattered and filtered in a way that emphasises the blue wavelengths.
Cosmetics:
When applying makeup, the appearance of the product can vary under different lighting conditions due to refraction and scattering. Foundations and concealers are formulated to complement the natural refractive properties of the skin, aiming to provide a consistent look across various lighting conditions.
Medical Treatments:
In laser treatments, understanding refraction is crucial for targeting specific skin layers. Lasers use specific wavelengths to interact with pigments or tissues at different depths, requiring precise control over how light refracts within the skin.
Micropigmentation:
The appearance of micropigmentation can change based on how light refracts through the skin above the pigment. Thicker skin or more pigmented areas may alter the perceived colour and clarity of the treatment.
How we view micropigmentation is based on many areas, how deep we implant pigment in the skin to how that light is reflected into the viewing eyes, the needle configuration and the amount of saturated pigment, the pigment mix we have chosen.
Bright sunlight or overcast days compared to indoors and artificial lights will have an effect on the pigment as we view it.
There are so many factors that cause pigment to fade.
Naturally, pigments are designed to fade somewhat over a period of time.
This allows the technician to make small changes every so often over the years.
However other factors will also fade pigment.
One of those biggest factors is UV rays. The continued effects of UV rays entering the body and slowly breaking the pigment down. This can cause loss of colour and colour change leaving you with an unwanted residual colour within the skin.
Internal factors can also play a roll. The cells (macrophages) which patrol the layers of skin to capture any foreign objects and build and crowd around the pigment causing a loss of appearance to the pigment. Lifestyle and smoking can lessen the oxygen in the blood and cause the blood to look darker/cooler.
Skin penetrating treatments and products can interact with pigment, medical conditions, medications and ageing skin. So now you are beginning to understand there is more to this picture than you originally thought. It’s a mixture of all of the above and then how we visualise colour. Your ability to see the full-colour spectrum and your brain's ability to chemically process what you see.
The conditions you view the micropigmentation in, sunny days or cloudy will also play a role! Yes, it seems strange to think of all of these possibilities, and how much or how little they can affect what we see. If you would like to understand more about colour theory, how pigment sits in the skin and how to correct colour why not purchase our Pigmentology course!
Resources:
https://sciencenotes.org/tyndall-effect-definition-and-examples/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10807857/
