Basic color theory
To fully understand how light works, we need to have a basic understanding of what color is and how different colors interact with each other. The study of this phenomenon is known as color theory.
What is color?
When light comes in contact with an object, the object absorbs a certain amount of that light. The rest is reflected into the eye of the viewer in the form of color. The easiest way to visualize colors and their relations is in the form of a color wheel.
There are millions of colors, but there are only three colors that cannot be created through color mixing—red, yellow, and blue. These colors are known as primary colors, which are used to create the other colors on the color wheel through a process known as color mixing. Through color mixing, we get other “sets” of colors, including secondary and tertiary colors.
Secondary colors are created when two primary colors are mixed together. For example, mixing red and blue makes purple, red and yellow make orange, and blue and yellow make green.
It’s natural to assume that, because mixing two primary colors creates a secondary color, mixing two secondary colors would create a tertiary color. Surprisingly, this isn’t the case. A tertiary color is, in fact, the result of mixing a primary and secondary color together. This gives us the remainder of the color wheel:
There are other relationships between colors that we should know about before we start using Blender. The first is complimentary colors. Complimentary colors are colors that are across from each other on the color wheel.
For example, red and green are compliments. Complimentary colors are especially useful for creating contrast in an image, because mixing them together darkens the hue. In a computer program, mixing perfect compliments together will result in black, but mixing compliments in a more traditional medium such as oil pastels results in more of a dark brown hue. In both situations, though, the compliments are used to create a darker value.
Be wary of using complimentary colors in computer graphics—if complimentary colors mix accidentally, it will result in black artifacts in images or animations.
The other color relationship that we should be aware of is analogous colors. Analogous colors are colors found next to each other on the color wheel. For example, red, red-orange, and orange are analogous. Here’s the kicker—red, orange, and yellow can also be analogous as well. A good rule to follow is as long as you don’t span more than one primary color on the color wheel, they’re most likely considered analogous colors.
Understanding color temperature is an essential step in understanding how lights work—at the very least, it helps us understand why certain lights emit the colors they do. No light source emits a constant light wavelength. Even the sun, although considered a constant light source, is filtered by the atmosphere to various degrees based on the time of the day, changing its perceived color.
Color temperature is typically measured in degrees Kelvin (°K), and has a color range from a red to blue hue, like in the image below:
Real world, real lights
So how is color applicable beyond a two-dimensional color wheel? In the real world, our eyes perceive color because light from the sun—which contains all colors in the visible color spectrum—is reflected off of objects in our field of vision. As light hits an object, some wavelengths are absorbed, while the rest are reflected. Those reflected rays are what determine the color we perceive that particular object to be.
Of course, the sun isn’t the only source of light we have. There are many different types of natural and artificial light sources, each with its own unique properties. The most common types of light sources we may try to simulate in Blender include:
- Incandescent light
- Florescent light
Candlelight is a source of light as old as time. It has been used for thousands of years and is still used today in many cases. The color temperature of a candle’s light is about 1500 K, giving it a warm red-orange hue. Candlelight also has a tendency to create really high contrast between lit areas and unlit areas in a room, which creates a very successful dramatic effect.
Incandescent light bulbs
When most people hear the term “light bulb”, the incandescent light bulb immediately comes to mind. It’s also known as a tungsten-halogen light bulb. It’s your typical household light bulb, burning at approximately 2800 K-3200 K. This color temperature value still allows it to fall within the orange-yellow part of the spectrum, but it is noticeably brighter than the light of a candle.
Florescent light bulbs
Florescent lights are an alternative to incandescent. Also known as mercury vapor lights, fluorescents burn at a color temperature range of 3500 K-5900 K, allowing them to emit a color anywhere between a yellow and a white hue. They’re commonly used when lighting a large area effectively, such as a warehouse, school hallway, or even a conference room.
The sun and the sky
Now let’s take a look at some natural sources of light! The most obvious example is the sun. The sun burns at a color temperature of approximately 5500 K, giving it its bright white color. We rarely use pure white as a light’s color in 3D though—it makes your scene look too artificial. Instead, we may choose to use a color that best suits the scene at hand. For example, if we are lighting a desert scene, we may choose to use a beige color to simulate light bouncing off the sand. But even so, this still doesn’t produce an entirely realistic effect. This is where the next source of light comes in—the sky.
The sky can produce an entire array of colors from deep purple to orange to bright blue. It produces a color temperature range of 6000 K-20,000 K. That’s a huge range! We can really use this to our advantage in our 3D scenes—the color of the sky can have the final say in what the mood of your scene ends up being.
What is chromatic adaptation? We’re all more familiar with this process than you may realize. As light changes, the color we perceive from the world around us changes. To accommodate for those changes, our eyes adjust what we see to something we’re more familiar with (or what our brains would consider normal). When working in 3D you have to keep this in mind, because even though your 3D scene may be physically lit correctly, it may not look natural because the computer renders the final image objectively, without the chromatic adaptation that we, as humans, are used to.
Take this image for example. In the top image, the second card from the left appears to be a stronger shade of pink than the corresponding card in the bottom picture. Believe it or not, they are the exact same color, but because of the red hue of the second photo, our brains change how we perceive that image.