Monday, June 18, 2012

Horrible Tutorial #2 - Concepts of Light

This is basically a photography lesson about light. Using Cycles you need to understand how work with concepts that work in real life film, and where cycles lacks in recreating real life light.

In this tutorial, I'll go over the basics of lighting a scene, emotions, and temperatures of light. I'll describe the proper way to light a scene and how to get the most from your images and animation to work with the emotion you want to create.

After the break, will be the video, and a lengthy few paragraphs about light and how it works...

This is not intended to teach you the details of using emitters and modeling, it's just how to work with lights in a scene and make a well lit scene, even dark scenes, with well lit subjects.

First we need to look at how light works:

Real life
According to Wikipedia:
Visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has a wavelength in the range of about 380 nanometres to about 740 nm – between the invisible infrared, with longer wavelengths and the invisible ultraviolet, with shorter wavelengths.
Primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, and polarisation, while its speed in a vacuum, 299,792,458 meters per second, is one of the fundamental constants of nature.
Visible light is emitted and absorbed in tiny "packets" called photons, and exhibits properties of both waves and particles

In cycles, light is attempted to be accurate by using Light Path Expressions. As defined here:

I won't go into the details, but understand that the way it works, is to trace a random spot on the screen (generated by the seed, and a randomizer) point it directly at the scene, and follow how many bounces it takes till it hits a light source. That ray is then multiplied with the other rays for that same pixel and generates a two dimensional image like a photograph.

To make it simple, it's reversing the path of photons of real light to generate the image.

The Major Differences
Cycles "reverse photons" don't carry anything more than a few parameters of light; Intensity, Direction, and Color (frequency). The wavelength, polarization, and speed do not exist to cycles.

Because of these missing parameters, we lose some things about real light; dispersion by refraction. Or, for example, how a prism creates a rainbow from a white light source.

We also lose information about falloff of light intensity by wavelength, thus red light will travel as far as blue light in a scene, producing less accurate lighting. Imagine a street scene, from a helicopter, at night you would barely make out green and yellow lights from stop lights, but red normally blankets these scenes. Red can travel farther than other colors, due to its wavelength and lack of dispersion through air. If you were to recreate this scene in cycles, with the same origin emitter intensities, you would see just as much green as you would red, which is inaccurate.

So what?
So when we create a scene, in cycles, we should verify with reference photos to assure accuracy of a scene, if we are trying to be accurate.

Of course, if your scene is to be purely fictional, then you make it as you like...

Physics behind us, let get into some concepts of lighting:

I assume you've seen the preface to this tutorial about professional lighting of an indoors scene. Taking note of the setup and surroundings. If you haven't, I highly recommend you check it out.

Here's what I'll be going over in the video:

Basic concepts
  • 3 Point Lighting
  • Soft and Hard light
    • Soft light, large, farther source
    • Hard light, small, closer source
  • Diffusion Bouncing
  • Shadows and silhouettes 
    • Light Falloff (further from a light source the darker it gets)
    • Textures and Direction; Front light removes depth, side light emphasizes depth. 
      • I forgot to mention this in the video. How sad! Just know that light can emphasize textures and bump maps, and make it look like it has more depth. BUT don't rely on light to do it all, your material may need to have some darkness.

  • Colors can emphasize temperature.
  • It can also emphasize emotion.
    • Warning lights
    • Emergency lights
    • Peaceful and Holy
    • Evil or Sinister
  • Download the Modified Blend File
    • The original from is at the bottom of this page.

How to Light Your Scene
  • What is your subject?
  • What is the emotion/feelings you want to convey?
  • What is your surroundings?
  • What is the temperature you want to describe?
Understanding these concepts can help you portray your scene to the audience without having to give other contextual clues to the surroundings, generally people know these feelings when they see them, but may have a hard time describing it.

Here's the still renders shown in the video:

3 Point Lighting Example

Red Lighting (Emotion: Evil)

Yellow Lighting (Emotion: Warning)

Blue Light (Emotion: Natural)

Red Light (Emotion: Disaster)

Bright Lights (Emotion: Comforting)

Bright Lights With Gloss Floor (Emotion: Clean, Pure)

Bright Lights With Diffuse Floor (Emotion: Warm)

Three Point Light - Natural

Three Point Light - Dark

Three Point Light - Warm

I used a blend file from in the video:
Thanks to mcavady for providing this scene to the community.


  1. Hello! Nice tut, clear understandable speech without any annoying lithsps. And you seem very thorough! I have to say though, from the position of the camera in your 3pt setup you seem to have the fill light and the backlight mixed up when you are describing them. By definition the backlight is only to illuminate a tiny sliver from behind. You described this light as the fill light. And the one you said was the backlight is really more of a kick light since it contributes to the shading on the front of the subject. It is also noteworthy that the keylight is generally placed above the subject unless you want sinister, bold, or firelit shadows, and the fill light is usually placed level or below because it's function is to soften shadows and contrast. It would be much more common to place the key above. At any rate I look forward to seeing more of your tuts and seeing where you go with it. Good luck!

    1. Thanks, yeah when doing a tutorial, some times words get mixed up...

      Honestly, I was taught, key light to light your key objects. But it's the concepts not the terminology I was going for, as a lot of the time lighting is hard for people to grasp. Understanding some simple ways to give your scene more or proper light is just what they need.

  2. Aw that's dam cool and np it was about time a I gave a little something back :) like it