Physics/Science of Light (PART 1)
Understanding the Behavior of Light in the Real World
(How you could implement it + create dramatic compelling artistic scenes)
Let me first start off with a personal note mentioning that I have done extensive research to comprehend the phenomena of light. Implementing this type of knowledge I'm about to offer you can greatly enhance an visual artist's artwork in particular. Curiosity and a relentless appetite for knowledge is the driving force that will set you apart from other artists.
Art can be a source of knowledge, a well structured diagram of internal thoughts; offering a thought provoking, and intuitive experience. I'm sure Plato would not agree with this statement as he refused to accept art played a role in our intellectual development."Art as a source of knowledge" would not pass with Plato. However Leonardo da Vinci certainly thought otherwise; it was an accumulation of his scientific research and experiments. These experiments were transferred unto paper in order to visually demonstrate his experiences. Known as the great Italian polymath he recorded what he saw as accurately as he could with sketches and highly detailed drawings. Sometimes words alone cannot explain everything. We are visual creatures after all. Personally, intuition, disciplined deep thought, structure and research enables me to create properly structured story telling visuals.
I'll try not to digress-back to what I was saying initially. I often realize that only reading, watching lessons or listening to information (through audio books) do not guarantee the information will be entirely comprehended. I become circuitous, long-winded, and redundant with my explanations and I could never explain the information in concise simple terms. As Albert Einstein once quoted, "If you can't explain it simply, you don't understand it well enough". Which was my case.
So I decided to make it a priority for me to start summarizing my research and explain everything I've learned (double-checking, perhaps even triple-checking, just for good measure, because I have OCD when it comes to details and accuracy). With that being said, it may help you too.You win I win-we all win together.
Hopefully this aids artists out there and gets them more comfortable with rendering scenes that are more imaginative, appealing and innovative. As painters you should not be limited to only relying on references to create art; it would be a shame for an individual with a souring imagination unable to present it outwardly for the world to experience.Nevertheless, here is the culmination of the research I have partaken in: in the most simple way I could explain it.
1. Properties of Light and Lambertian Reflection
Understanding how to create compelling art scenes with different lighting schemes and dramatic shadows is critical to a proficient artist. We should try to understand the physical interactions light has with various surfaces and textures and how our eyes and brains react in order to interpret information. Also how we can make scenes visually appealing.
Light is something we don't know everything about, just like gravity and energy. Scientists have compiled a few equations for predicting the behaviour of light and they 've calculated a few things about it but never could it be thoroughly understood. It has multiple attributes and patterns of behaviour but sometimes it behaves like a wave and sometimes it behaves like a particle.
The Principles:
It's important to understand the principles light runs by but it's not necessary to understand every scientific hypothesis (the equations) that was ever created to explain it's behaviour. Getting a grasp of the foundational elements and how light interacts with the world is necessary to create impactful art scenes.
Quantum basically means that something is unpredictable at a microscopic level. How will a little atom floating around interact with another atom? Well,we don't exactly know what's going to happen with any given atom.
Quantum Physics
But there are probability fields surrounding these atoms that say how much probability there is that the light is going to be reflected at a certain angle and how much probability there is that a surface will take on a certain colour.
When you have particles and light in large masses then those probabilities become predictable fields and you can expect a certain result over the way a large area would react to a light.
When we refer to quantum we are investigating how something is dictated by probability and the ability to see a consistent result on a larger scale.
Photons
What is a photon?
A photon is a particle of light -you can imagine it as a billiard ball zipping along in a consistent direction in a very high speed (at around 186,000 miles per second-which is extremely fast).
When light hits something (like a surface) there's a predictable pattern of how it's going to bounce off of that surface.Keep in mind the predictably pattern is also dependent on the the type of surface the light is going to be interacting with.
Light Vector
Let me briefly explain vectors. It is a 3 dimensional angle in space. So when I talk about a vector of light, it is energy/light that is floating in a 3 dimensional space. It's important when trying to understand light that you can think in 3 dimensional space in your mind's eye, and to always picture 2 dimensional objects in 3D.
Reflection:
is the bouncing behaviour of the photons that are not absorbed by the surface that they hit.
Fall-off:
is the speed at which objects go from light to dark. Does the light exposed area of the object abruptly convert to shadow or does it gradually blend from light to dark? There are different rates of fall-off and usually that rate of fall-off is influenced by how much of the object is being exposed to light as well as the angle it is facing the light.
Properties of Light:
Lambertian Reflection
Light has proportions of both a wave and a particle. When discussing form, it helps to think of light sources consisting of particles like bouncing billiard balls. When we're discussing form and lambertian reflection, we want to think about light like a billiard ball that's flying out in the constant direction from a single light source (radiating out from that central position of the light source).
These photons will fly in a constant direction until they crash into something, such as a plane in space. Let's say this plane is not shiny, but has a matte surface with microscopic irregularities all over its surface.
When these photons meet the plane, some will get absorbed, but the rest will deflect in random directions because of those tiny irregularities. Because there are countless photons, a generous amount will reach your eye to make the plane appear as a solid value.
Usually there are so many photons (trillions and beyond) flying out over time from any given light source. Any surface that is not affected by light is going to appear as invisible, the only way we can see something is when light comes from a light source bounces off the surface (of the object) and enters our eyes. Then our brain is able to interpret the information the light is giving our eyes.
With a lambertian surface, the light will fly at a constant direction then bounce off of that surface; which will result in a constant colour (on that surface). That surface basically becomes a particular value and colour as a result from that light hitting it, bouncing off of it and the reaching our eyes. Another way to think about lambertian reflection is just a matt surface.
As shown above, as the angle of the surface turns away from the light, fewer photons are able to directly strike that surface. Fewer photons scattered means fewer reach your eye-making the surface appear darker.
If you assume that the photons travelling in space are distributed fairly evenly (which most light sources should be-at least to our eyes) that even distribution is going to cause (on a surface that is facing towards light or perpendicular/relative to the light source) that surface to be brightest. A surface that is perpendicular to the light source is going to be the brightest, and as the surface angles away it receives less photons reaching that area. To reiterate, as the plane turns away from the light, it causes that part of the plane to gradually transition into a darker shade.
Referring to the example, when the surface is broken down into a bunch of chunky flat planes, it's pretty easy to see this effect happening. Planes that are angled downward get darker as it turns away from the light. And as you increase refinement it's going to appear considerably smoother. And as those planes are turning progressively further from the light the planes will get darker and darker until they reach the point of the terminator (or terminus). The terminator is usually at the half way point on a round object like a ball.
All objects are made out of planes. You can imagine any portion of a surface as its plane counterpart;angled in space relative to the light source. Sometimes painting a sphere in your lighting schemes and then translating those lighted angles to other surfaces is helpful.
In practical terms, there are usually multiple light sources, so shadow areas are seldom black. Of course, you have other effects to consider like surface colour and reflectivity (specular highlights). But as a base layer, diffuse highlights are the foundation for accurate rendering.
If you can learn to think in three-dimensional in this way, you can cognitively solve any diffuse lighting problem. Even complicated curved surfaces can be broken down into individual planes if necessary to solve lighting problems. That 50% point (dividing light and shadow) on the object is basically the point at which any photons flying toward the object cannot land on any of the planes facing the opposite direction from the light source. Usually you'll have a distinct terminator line (a definite cut-off point) dividing the light part and the shadow part of the object.
The place where the planes face the light is often called the center light or the diffuse highlight.
The place where the planes cease to face the light is called the terminator and can be mapped out if necessary.
Lights and Shadows:
There are three attributes of light sources that affect how they wrap around the objects in your painting:
1. Sunlight, spotlights, and distant sources:
This light type gives you soft-edged form shadows but hard-edged cast shadows. Thinking in three-dimension is essential for figuring out where the shadow will be cast. Essentially how it works is you have a light source which sends out light rays in an evenly distributed parallel direction; all the photons streaming out are parallel to each other. This causes the cast shadow to be the exact same shape and width of the object being hit by the parallel waves of photons.
2. Nearby Light Sources:
As light sources near an object, the shadow narrows in size and the terminator approaches the light source. If the light source is small, like a candle, the cast shadow will be hard-edged.With a nearby light source on the other hand, it's going to have a much larger cast shadow because now those rays are no longer parallel to each other.
And "nearby" can be a relative term depending on the size of the object. Another observation that we can learn from is that the terminator on the ball lit by the nearby light source is at a much higher position in comparison to the ball hit by a light source that is further away (like a spotlight light source).
We can also see that with the nearby light source, it casts a shadow that is much larger in width and also height.
3. Oversized or diffuse sources:
The larger the light source is, relative to the object, the more the terminator moves away from the light source and the softer-edged the shadow becomes. This is because the light doesn't reach every part of the shadow area equally, since the object occludes part of the light in the area behind it.
On the other hand if you have a large light source, you're going to get light rays that are radiating in several arbitrary directions from it. This causes the rays to reach at several directions and angles of surfaces so as a result the cast shadow sitting right beneath the ball is very minimal and soft in appearance. One way you can approximate this is that you can imagine a circle of light radiating from the light source and figure out how far they would go as well as how they would overlap. You can approximate it pretty well if you just look at your light source. Figure out where those photons are going to be travelling so that those points that you mark at which the photons hit will be the extent of the softness of your shadow.
Of course, any part of the ball that is able to block out the majority of the light is going to be pretty dark. This is the light source that you'll frequently come across and be working with.
Ambient Occlusion/Dynamic Occlusion:
When you have an ambient light source filling in your shadows you can see
that the shadow cast by the ball isn't completely black, instead it's filled in with some light (reflection). Some of it is light bouncing off the surface next to it and some from the room around it.
Every time the light is coming in and bouncing off of a surface (either unto the ball or unto the ground) the light loses a lot of its strength and energy, (generally speaking around 90% of the brightness of the light is lost with each bounce).
Every time the light hits a surface it loses 90% of it's strength and brightness. As a result it's very difficult for light to get down into the deepest cracks of the surfaces.
Remember that cast shadows aren't black, they're filled with the other light in the environment. Sometimes it helps to figure out what the object looks like under the main light source first so your shadows will be true to the scene.
Another point to remember is that usually there is ambient light in almost every scene, and because of that, the cast shadow will not be purely black.
Nearby Sources:
Photons radiate evenly in all directions from the source; spreading out with distance. This means close objects receive more light, and darken as they recede from the light source. When you have a nearby light source and a flat plane, that flat plane will not have a solid colour.
However, when the light rays are parallel to each other and hit a flat surface, that surface will remain one colour (as shown below).
But in this case, (as shown below) you have a nearby light source where the rays are radiating outward from it. They are no longer parallel but equally distributed apart from each other. In this example, the surface closest to the light source is going to be brightest and the areas further from the light will be darker.
Another thing that's going to affect your lighting in your scene is the perspective of the viewer (so even if you have a light source that sends out waves that are parallel to each other and the same objects distributed evenly-they're going to be lit differently depending on which angle our eyes view the objects. It is easy to see how the terminus' position changes on each ball depending on the angle it is located relative to the viewer and the light source.
The information presented here is only the basics of light's physics (part 1),I"ll provide much more advanced in-depth information in the next blog post.Stay tuned for part 2 of "Physics/Science of Light" by subscribing to my newsletter.
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