The Behavior of Light In Art

The Behavior of Light In Art

We’re born with the ability to view beautiful sights, scenery, and the world around us through a very important matter: light.

Perception is only possible through the nature of light’s interactions with the environment and with itself, allowing us to appreciate the exquisite art that came out of artists studying light. Consequently, the study of optics explains much of the behavior of light’s movement.

Our eyes process the intersection of light converging into a singular point, refracting through our cornea and lens to our retina, to form an image (Smith & Atchison, 1997). More specifically, a real image is formed when light rays converge to a single point. On the other hand, a virtual image is formed when light rays diverge from an optical system like a lens. When you trace those diverging rays back to a single point where they meet, the image is virtual.

We can observe real objects and virtual images in the below example. Here, the brighter camel is a real object as actual light rays come from the camel. On the other hand, a less bright camel upside down is a virtual image as you can see the backtrace of light by those dotted lines.

Another example of a real object is a laptop in front of you; since you are able to see and touch it. A virtual image, conversely, is something you cannot touch——think of virtual images like virtual reality games in the way that you cannot physically touch what you see. Hence, the image of you in the mirror is virtual because light rays reflected back from the mirror diverge, and those backtraced rays lie behind the mirror. Light can either produce virtual or real images.

This article explores the science of how we’re able to perceive colors and images in art, and explain common observations whenever we look at references of artist’s depictions of observed phenomena.

Within this article, optics questions are addressed: from a physics perspective, how are we able to use our eyes to experience and see art?

As an introduction, it would be beneficial to break down the fundamentals of light.

Light is a wave of electromagnetic radiation traveling through the world around us, and is responsible for optical phenomena like our perception of colors. The wave model of light accounts for the visible spectrum of wavelengths which we are able to see. We can see between the red-violet wavelengths range. All red-violet wavelengths all combine together to compose white light.

For example, light creates a structural coloration optical phenomenon within the Menelaus blue morpho (Morpho menelaus), which has a distinct blue iridescent pearly color.

Structural coloration is where the organism’s biological structure defines its color. To be more specific, the colors are generated by how incident light (light coming in at an instant) interacts with the microscopic structure of the surface layers of an organism. Colors from this interaction end up more saturated and vibrant than pigments. Moreover, this raw light interaction contributes to why it parallels the background of why RGB colors are always more saturated than CMYK which will be touched on later.

This distinct appearance results from the butterfly’s wings covered in microscopic scales within multiple parallel layers. Between these layers, there is actually air and dense layers embedded (Piszter et al, 2016). Its color arises from the series of layers having contrasting refractive indexes (the degree to which it’ll affect light’s interaction to bend). As a result, the series of layers selectively allow the blue wavelength to be reflected and the other wavelengths are absorbed by melanin in the structure.

Understanding the composition of light is imperative because it explains how light refracts. This leads to different image formations for our eye to see, as well as differences in the color of light.

Properties of a wave include frequency (how many full wavelengths are completed in a second), period (duration to complete one full wavelength), and amplitude, which is the measured maximum, magnitude intensity of the wave measured from the equilibrium point to the crest or trough (Shukla, 2009). A high frequency of light has a short wavelength, and a low frequency of light has a long wavelength.

In colors, we see high frequency of light as blue and violet wavelengths and very low frequency of light as red, orange, yellow wavelengths. Long wavelengths have low energy, and short wavelengths have high energy. So, if you see the color purple or blue on your screen, those wavelengths of light carry high energy.

Do you ever wonder why your digital artworks when printed appear duller than on the screen? This is because of the properties of RGB and CMYK models.

RGB is a color model standing for red, green, and blue primaries where a huge range of colors can be created by additive color mixing.

CMYK is a color model with the acronym standing for cyan, magenta, yellow, and key (black) primaries. Through subtractive color mixing, the CMYK model can create a lower range of new colors compared to RGB.

Commonly seen in screen monitors, additive mixing is the addition of wavelengths by emitting light, producing a brighter visual outcome. On the other hand, subtractive mixing is subtraction of wavelengths by absorption of them, thus producing a duller visual image.

Colors are perceived due to reflection of wavelengths into our eye. For instance, we are able to see red because all wavelengths reflected by a medium are absorbed except for the red wavelength. The red wavelength is reflected by the medium into our eye.

RGB stands for red, green, and blue while CMYK is the acronym for cyan, magenta, yellow, and key (black).

In the RGB model, mixing red and green wavelengths will produce yellow. In the CMYK model, mixing red and green wavelengths will produce black, since those wavelengths get absorbed. Pigment inks are the source of the wavelengths for CMYK models, so they absorb wavelengths and reflect others. These models exist for different functions:  RGB is used by computers and LED’s because these devices create light rather than reflect pigments, while CMYK is used by printers as the inks absorb and reflect light.

Colors from the screen are more vibrant because it is the light source, whilst colors from printer ink are less vibrant due to subtractive color mixing (the more colors mixed, the more darked the color is) and having a smaller gamut (color spectrum) compared to RGB’s large gamut. As colors can be directly produced by the light being emitted from the screen, this enables saturated neon colors.

So, when printing artworks, be aware  the printed work will be less saturated. You can combat against it being too dull, but CMYK can never replicate RGB’s unique saturation.

If you are using an art program that enables conversion from RGB to CMYK such as Photoshop, Procreate or Adobe Illustrator, you can set the file to CMYK itself and see how the art will appear when printed (Click on the art program name for the link to see the steps on how to do it)!

However, on Clip Studio Paint, you are only able to preview CMYK as you are only allowed to paint in RGB color space, and on iBis Paint X, you are able to export the artwork to CMYK.

These wavelengths are then processed through the structure of our eye as shown below.

The amount of light entering our eye will depend on the shape and size of the lens. This is known as accommodation––the lens changes shape to accommodate for what we want to see, far or close. An aperture is an opening restricting the amount of light entering our retina. Our pupil, a hole in our iris, acts as an aperture. This parallels a camera’s aperture (the hole opening at the front of the camera) allowing light to enter at different amounts to create a clearer image.

The retina is the most significant region of the eye, as it is located at the inner neural layer carrying its signals to the optic nerve to the brain (Atchison, 2023). Similar to a camera sensor, which processes light rays into an image, it’ll sense the light rays going into the camera’s aperture.

Our retina does the image processing and is extremely light receptive. It has 10 layers containing cells, pigments, and nerve fibres, allowing for light to be scattered and be spectrally reflected. (Atchison, 2023). With light being scattered and spectrally reflected on the retina, this helps as many rods and cones––light-sensitive photoreceptor cells––to absorb the light.

The very back of the retina contains these rods and cones.

We have about 100 million rods and 5 million cones at our retina. When light hits the back of the retina and light is scattered, the human eye has 3 cone variations that receive that light - this is the first stage of processing colors. These cones are the long, medium, and small wavelengths that determine the colors we see. Those rods and cones get stimulated by the light rays that get absorbed by them and transmit a signal to the optical processing regions of our brain.

Our best visual performance is emphasized by the intensity of light levels as both cones and rods create vision. Our cones allow for color sensing only when there are high intensities of light like in the daytime, and our rods cannot sense color for low light intensities of light in the dark. This explains why color is muted in low light environments because in the dark there are low light levels so our rods play a more prominent role here than cones as they are responsible for vision in the dark.

We humans are trichromatic because we have three types of cones. Most mammals are dichromatic, meaning they have two types of cones. Mammals that are dichromatic need only two cone cells to be able to see their visible gamut (color spectrum).

Now, let’s look at why we can see objects further or closer depending on the medium!

In this artwork (Figure 9), you can see how the artist Paul G. Oxborough has depicted  the bottom part of the character’s body closer to the surface. In particular, their left leg seems closer to the surface––but in reality, their body would actually be further down.

When light hits a medium, it can either be refracted, reflected, be absorbed, or transmit through the medium (Atchison, 2023). These differences in how light interacts with a medium arise due to mediums possessing distinct properties, such as density and opacity.

Light travels 3.00 x 10^8 metres per second in a vacuum, i.e. in the absence of any other particles (Keating, 2002). We can describe the influence of a medium on light’s speed through a ratio between light’s speed in a vacuum in relation to its speed in the corresponding medium - known as the refractive index, n. We can see this in Figure 10.

A higher refractive index demonstrates that the medium has higher optical density. Likewise, a lower refractive index expresses that the medium is less dense. For practical purposes in calculations, we take air as 1 and water as 1.33 (even if air isn’t 100% value 1 we just use that number for practical purposes). The higher number, 1.33, corresponding to water, would possess more density.

It is worth specifying that we consider optical density and not mass density, since a low mass density can still give you a high optical density. Optical density describes the degree a medium will affect light’s interaction while mass density is how tightly packed the atoms in a medium are together. For instance, moissanite is less dense than diamond, but has a higher refractive index.

When light enters from a medium of lower density to high density, its speed will decrease.

Light can be documented as rays, which are a visualisation of the direction the light rays are propagating illustrated as straight lines. Furthermore, they can be displayed as wavefronts–– a joining of points where multiple light waves are at the same phase in time. Displayed as a curve and by “same phase”, the curve appearance can mean two light waves at a certain instance of time are at their crest or trough.

Perpendicular to the surface of the medium, there lies an invisible line called “the normal”.

When light travels from a high refractive index to low refractive index, its speed will increase. This causes light to bend away from the normal (Keating, 2002).

Visually, you can see that the incoming light ray from water to air has bent away from the normal.

In Figure 13, light rays are coming from the chicken (object) from water, and exit the medium into air.

We can see the light rays' departure from water, as well as their extension back down to where they intersect. This is because our eyes interpret light travelling as straight lines in our eye. The produced virtual image is located closer to the surface than where the actual object is.

If you are illustrating objects in a medium such as water, it would be beneficial to distinctly include how objects will appear closer to the viewer!

Other cool optical phenomena can be atmospheric such as crepuscular rays. These are commonly seen in dispersed rays artworks.

This optical phenomena results from the scattering of light in the air and our perspective of the light. The rays appear to be diverging due to perspective, similar to how we see parallel railroads as converging when viewing them far away (Bohren & Sowers, 1992).

Understanding the nature of light allows us as artists to appreciate observed phenomena and  make insightful decisions. RGB and CMYK models are incredibly important to consider  when making  prints. Alongside this, they’re great for predicting whether an object will appear closer or further to the refractive index of mediums, allowing our imitations of our observations to be more accurate. Making observations is such a fundamental part of an artist’s ability to manipulate their imaginations into an artwork. So, next time, if you see these optical observations like crepuscular rays or closer looking objects underwater, you’ll understand how they work!