You may think that outdoor lighting is more difficult than indoor lighting. I would actually say it´s the other way. Outdoor lighting is much more simple to achieve!
Let´s pretend you´re a photographer and go out a sunny day with a digital still camera. Yeah, you got that right – you can´t move the light! The sun is where it is – and you can´t do much about it. The only thing you can do, is to move your models, and your camera.
Now, while walking around, we notice a car. It´s hit hit by the sun and casts a nice strong shadow. But take a look under the car. There´s a secondary shadow underneath! Where does that come from? This is the secret with outdoor lighting. We have two light sources, not a single one.
We have the sun light, which is a small and sharp light source. And we have the sky – which is a huge light source – thus producing soft shadows. Just like the one underneath the car.
Luckily, we can move the sun in our 3D scenes, but really – that´s the only thing we need to move. The sky light will always surround the scene in a similar way – no matter if the sun is there or not.
So how do we set up the lights?
For the sun, a bright orange colored Distant Light will do just fine. At mid day, it´s high up in the sky and aims almost straight down. Closer to evening, it´s lower in the sky, with a more deep orange color, almost touching the red spectrum.
And the sky? There are several ways of doing this. One is to add a sphere object into your scene and map it with a 360 degree panorama – which can then be set to emit light via Radiosity. This would automatically lit your scene and mimic the sky light.
The other way, would be to simply add an area light above your scene, and make sure it´s big enough to cover all of it. Add a bright bluish color or a more greyish one if you´re planning on doing an overcast scene.
We can add ambient light – an even all over lighting to mimic the overall light bouncing that occurs outdoors – but we don´t have to.
You can render with or without Radiosity. The latter will of course take longer, but will give more realistic results, as Radiosity will calculate all the light bouncing going on. Balance the sun and sky lights with a strong enough Radiosity setting and you´re done.
If you want to get more professional results, try adding the sun so that it hits your scene from the back, side and above. Professsional photographers use this to enhance the silhuette of the models, so that they break away from the background. You can then add an additional light coming from the same direction as the camera, to lighten up the shadows on your model. (Like using a bouncing reflector in real world photography).
And that´s it! Midday, outdoors lighting is my favorite lighting set up. It´s just THAT easy!