Introduction

The first thing to understand when expressing light in art, whether painted or cel in style, is how light behaves. In this tutorial, I will explain a few different concepts of light, to help you better understand how to express it in your art.

First Concept: Light Travels In A Straight Line

Light travels outwards from a light source in a straight line, until it hits some kind of an object. When it hits something, a little bit of its energy gets absorbed, and the rest of it bounces away until it reaches our eyes!

 

There are two different kinds of shadows that form as light travels and bounces, labelled in the above image.

 

1. FORM shadows (yellow)

As the form of an object turns away from the light, less and less light is able to reach it. This creates a SOFT, gradual gradient into the darkness.

 

2. CAST shadows (red)

When light hits an object, if it's opaque then the light will bounce off of it and not be able to pass through. This means the light cannot reach the areas being blocked, creating SHARP shadows.

If we think about what areas are turning away from the light and what areas are being blocked from the light, we can block in our areas of shadow where the light can't reach

Second Concept: Bounced Light

As mentioned before, when light hits something, it bounces off of it and gets a little bit weaker every time it does. It also changes colour, inheriting the colour of the surface it bounces from!

 

We can easily test this out and see it in real life by shining a bright white light onto a coloured surface and holding a piece of paper close to it

The bounced light is much weaker than our light source, which means:

 

1. We can't see it anywhere that our light source is hitting, because our light source outpowers it.

In other words, bounced light is only visible in the shadows!

 

2. Bounced light absorbs the colour it's bouncing from, changing the colour of the light. When our white light hits the blue surface, the light becomes blue!

Light will bounce all around our environment, eventually weakly hitting the shadows of our object. We can add just a hint of colours from our environment into our shadows to depict this bounced light.

 

NOTE: bounced light will ALWAYS make shadows LIGHTER. Watch your VALUES when adding colour to the shadows, and ensure it gets LIGHTER.

Third Concept: Light Fall-off

This is a very simple one! As light travels, it loses energy and grows weaker. The further away from a light source, the less bright our highlights will be and the lower the overall contrast will become. To create a sense of depth in your image, use darker values the further away from the light, even when the light is hitting that surface.

Fourth Concept: Different Surface Textures

A smooth object is shiny and reflective because the light that hits it immediately bounces back away with minimal loss of energy in almost the same direction it hit it at, so it's almost exactly the same light that hit it in the first place.

 

A rougher surface is filled with all kinds of nooks and crannies and bumps and divets that disrupt the light and make it bounce around wildly, and every bounce the light does makes it weaker and weaker, until the light is almost entirely gone!

 

This means that on smooth surfaces, there will be a greater range of values and influence of environmental colours than on a dull surface.

Finalising

Through the combination of FORM and CAST shadows, along with Surface Texture, Light Fall Off, and Bounced Light, we can create a convincing expression of light!