In any scene the appearance of a subject is affected and highly dependent on the positioning of the lights.
Suppose you have a lamp as a light source, the manner we "position it" directing it at the bottom or at the top right or left of the subject, we intervene in the appearance of its aspect itself.
Generally overhead (from above) lighting and front turns out to be the best manner to give a more natural look.
Low lights on the subject of interest make it gloomy, almost sinister.
However in most cases, in the field of professional lighting, one opts for a "mixed" choice where the lights are placed in different positions. This system favors the creation of a set of hard and soft lights that give depth and realism to the scene.
To illuminate a subject correctly, you must use a minimum of three lighting (lamps) in the figure below you see how to arrange them, but at least a Key and a Fill light are paramount.
The main light (key light) is the main light illuminating the subject, is the strongest source of light and is generally positioned to the side of the camera.
fill light is used to spread the light on the subject achieving an effect of softness that reduces hard and sharp shadows created by the main light. The fill light is usually positioned on the other side of the camera than the main light and usually has less power than the main light.
back/cut light is used to illuminate the back of the subject in order to "disconnect" the subject from the background and then give more realism to the scene. This light, usually, is positioned exactly at 180 degrees, on the opposite side of the Key light.
The Key and Fill lights angles can vary.
Keep this in mind when u are setting up the complete scene set up, this is a set up for the global scene and not eg an interior area inside your global scene.
Its a method that can add drama or realism to a sun sky system , but in the context of eg a cave only interior scene it can serve eh same precise purpose and help you to add elements that placed in a smart way will add interesting dramatic visual details complementing there point of interest of your scene, or the point of interest itself, eg a single statue inside a dark room, or a supercar inside a fancy showroom.
You can create dramatic and immersive light set up for horror themed or historical themed scenes just the same
hard and soft light light
As definition, hard light, is that which is direct, it creates such a sharp contrast between the framed object, and its shadows. It is used generally, for a strongly pronounced definition of surfaces, and thus, for its characteristics, increases the overall illumination of the object.
The natural lighting of the solar rays is an example of a hard light.
As opposed to the harsh light there is scattered light, or soft, that fades and softens the contrast of shadows. It is used to dampen the strong tones of hard light; also it can be used to balance the overall lighting set of a scene.
The sunlight during cloudy days is a classic example of soft light.
An example of a hard light is that which is created by using a spotlight mounted above the camera. In fact, the spotlight light is unidirectional, and is projected directly on the subject creating precisely a sharp contrast between light and shadow.
If you interpose a diffusion filter between the light and the subject, this will turn into soft light.
Another system to obtain a diffuse light is to use a reflector, as can be, for example, a white billboard or an umbrella like diffuser as done in photography or simply just a wall because it is available in your scene.