Lighting usually refers to the source or sources of simulated illumination in the scene.
The four main family types of lights:
Ambient lights (Including Global Illumination)
Before getting into specifics, there are a few settings that we should talk about.
Like when modeling, your renderings will have a global scale. This goes for environment, lighting, material, etc. This is particularly important to lighting as the “bulbs” in your scene use the same global numbers. So 1 = 1. So 1 watt, is the same scale regardless if you are working at 1mm or 1 mile. This is something to keep in consideration. Lights can be adjusted for not only brightness, but color, shadow type, fall-off, and lots of other settings. We are going to focus mainly on brightness and visibility. (You can have lights that are on in the scene but with things like directional lights, you can have them cast light, but be invisible. This helps light up areas that are walled off from globally illuminated areas — such as closets and other rooms.
The most common example of ambient light that I can think of is to go outside on a cloudy day. Notice how there really aren’t too many distinct shadows? This is because the light is bouncing all over the place using the clouds. This is a great example of of ambient lighting. When you add an ambient light to your scene, it is like adding a general brightness to your scene so you can see what is going on. This is great as a base light to set moods and tones. In most rendering software packages, the most common ambient lighting is called global illumination. This is light that comes from everywhere and can be set to match specific color temperatures. Rarely will you render a scene with just ambient light. This is more to fill the space than to be used as your prime illumination source.
Spot lights are what their name suggests. They are a subject specific light that is generally used to illuminate a particular area within the rendering space. Both the focus and the fall off can typically be controlled dynamically or numerically and depending on the settings of the scene will cast harder shadows than directional or point lights. But then again, it depends on your individual settings and the distance the light source occurs from the scene. In the example, you can see that the light is focused on teh center of the cube and based on the shadow you can make a determination that the light is likely to the left and above the cube. The cone of this particular spotlight has a hard fall off area between where the light region is and where it falls out into space.
Moving on, the next type of lights are known as Point lights. These lights have a single point of origin in space and cast out light in all directions from that point. Like the other lights, the brightness as well as the color can be controlled. These work wonderfully in conjunction with lamps and other modeled sources of light in a scene to create a compelling atmosphere in the render. In the rendering shown, you can tell that the light is originating from a point shortly away from the center of the cube’s front face. When using these lights it can be tempting to use them as an ambient light source, but avoid this if possible as the shadows tend to be more distinct. But if that is the look you are going for, knock yourself out.
You can have this type of light cast light, but be invisible to the camera or you can have it turned on. You might want to turn the light on if you are trying to have reflections of the lights appear on the surface of your model if you are using a shiney material. Directional lights can be used as a primary light source to add drama and a more dynamic lighting condition to your scene. This type of light is also great for helping illuminate areas that are walled off from globally illuminated areas — such as closets and other closed off rooms. I tend to use this type of light the most in my renders as I feel it offers the most flexibility in both size and finish– speaking in terms of brightness and shadow quality.
There are plenty of other types of lighting circumstances that can be employed in your renderings. Things like HDRI (High Dynamic Range Images) can be used as a virtual sky for both lighting an compositing by turning the image into a light map based on the colors in the image.
IES lights offer a physically accurate spread of light that can be used for architectural rendering to simulate actual light bulb brands.
Free IES light viewer: