Yellow light and blue shadows

A common dilemma when lighting game objects is how to balance the intensities of ambient vs. directional light. If you choose a low ambient level with bright directional light, you get dramatic, well defined lighting, but the overall result risks being excessively dark, and it can be hard to see any texture detail in the shadowed areas:


If you choose more ambient and less directional light, the whole object is clearly visible, but the lighting risks looking flat and boring:


One useful technique is to give the ambient light a bluish color, while tinting the directional light yellow. This way the lit and shadowed areas can have similar overall brightness, but vary in hue instead. The entire object remains clearly visible, at the same time as the lighting remains well defined:


If you are using a traditional three light rig, where the ambient level is typically very dark or even zero, a similar effect can be achieved by tinting the key light yellow and the back light blue.

This change of hue from light to shadow can be exaggerated for dramatic effect, but also occurs in nature, especially outdoors on a sunny day. The Sun radiates many electromagnetic frequencies, including all possible hues of light, but when this light passes through atmosphere, red and green frequencies are not much affected, while the shorter blue frequencies are absorbed and then re-transmitted by gas molecules, which scatters them in all directions. Therefore:

  • When you look at the Sun from Earth, it appears yellow, because yellow light travels straight from the Sun to your eye, while much of the blue light is scattered in other directions on its way through the atmosphere
  • The sky appears blue, because some of that scattered blue light eventually happens to bounce down toward your eye, arriving in small amounts from all possible directions
  • Surfaces lit by direct sunlight thus end up with a yellow tint
  • Shadowed surfaces tend to have a blue tint, because they are indirectly lit by all that reflected light from other parts of the atmosphere

Comments (6)

  1. Jamie says:

    Its tidbits like this that make your blog a delight to read. Simple to implement; yet the possibilities are boundless.

  2. Andy says:

    I agree with Jamie – this blog is full of all sorts of useful  tips and techniques. Thank you and keep it up!

  3. Michael Hansen says:

    i see shawn have you read

    "Einstein and the Daytime Sky"…/daytimea.html

    i have this in januar 2010 and trying to construct this in xna

    and from my videos , we are getting there

    allways good blogs read , thanks


  4. Trent says:

    Great info Shawn. I constantly find myself looking at objects and wondering why I can tell it's sunlight on them and not some other source. Also noticing that dawn and more so dusk like is even more orange.

  5. Morten says:

    Agreed with Jamie. Simple tidbits everyone can understand and use independently of their expertise, but make a world of difference!

  6. Ryan says:

    Awesome.  This is why I love your blog!  Inspiration!

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