Light is great, it lets us find our sandwiches and saves our shins form being mauled by feral coffee tables and means we don’t all have to learn braille.
But there’s different ways to achieve illumination in our daily lives and different types produce different shadows.
If you’re painting a picture with shadows you might want to know what sort of shadows you should be using - Not all lights produce the same sorts of shadows. More, on the tutorial page at
http://www.cuprohastes.com/tutorials/2011/10/27/lighting-types.html