Putting the sun at your back at sunset or sunrise creates a front-lighting condition. Looking into the sun at these hours can create a rim or back-lighting condition. Most other hours will produce form-lighting.
The sun and the moon are directional point sources of light. Like an indoor incandescent light, they are (in practice) smaller than the subject they illuminate and create cast shadows. The sky on the other hand is a non-directional diffused source of light, larger than the subject and illuminating from all directions at once. Instead of casting sharp-edged shadows, a gray day creates penumbras, soft-edged shadows that gradually get darker as they get closer to the object casting. When the sun breaks out on an overcast day, the shadows don't get darker, the lights get lighter.
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| Some observations to consider under different outdoor lighting conditions. |
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| Detail from the above highlighting the difference between a point light source and a diffused light source. |
© John Ennis 2011
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