Secondary school physics teaches us that light is a wave motion or flow of photons, which represents two different and mutually exclusive theories, yet light behaves according to the laws of both. To meet the demands of filming, it is sufficient to understand the basic characteristics of light, such as intensity, colour, quality and direction.
Light can be stronger or weaker, which influences the exposition in individual cases. A light meter is used to measure the light intensity. Most modern video cameras have built-in systems for light measurement and indication of the amount of exposure.
Light can have different colours. For example, if we observe the light situation in a room lit by a classic light bulb as the evening light is coming through the window, we will most likely find out that the artificial light of the classic light bulb is “warmer” than daylight, which seems “colder” in combination with artificial light. Cold tones are blue, green and similar, the warm ones are yellow, orange and red. The colour of light can be measured and expressed in Kelvins, which represent colour temperature. However, be careful: warmer tones have a lower colour temperature and inversely. The colour temperature of a classic light bulb ranges around 2800 K, bluish evening light between 6000 and 8000 K. The standard for artificial light (usually marked with a light bulb) is 3200 K and that of natural light (usually marked with a sun) is 5600 K.
Light can be hard or soft, directed or dispersed. Point light sources (the sun on a clear sky is also considered a point light source due to its distance) will outline a picture with dark shadows and sharp angles. The “hardness” of the light therefore depends on the size of its source. A cloudy sky (a big source surface) will outline a picture with faint and undefined shadows with low contrast or there could even be no shadows at all.
You can learn more about the different functions of light in reference to its direction in the following chapter.
BASIC LIGHT POSITION
The basic common characteristic shared by photography, film and television is showing a three-dimensional world on a two-dimensional plane, mostly on paper, the cinema screen, TV-screen and similar.
In order to make a two-dimensional picture work as a realistic display of a three-dimensional world, it’s necessary to create an illusion of the third dimension. The viewer must feel the volume of the filmed persons and objects. Framing heights must be divided in order to conjure up spatial relations. Light plays an important role here.
Only one light source will usually not suffice to achieve the impression of the third dimension in the medium of photography. For that reason, light systems with more light sources were developed, which we rarely find in nature but they allow us to make filmed scenes look as natural as possible.
The basic light position makes up one of such systems. It’s built out of four light sources or lights, which are named according to their direction as seen from the position of the camera.
Key light (1), backlight (2), fill light (3) and background light (4)
The basic light position (BLP) is mostly meant for lighting the human face but it can also be used for objects or more complex situations.
It describes the volume of the filmed object. In this case, it is set on the position of three-quarter lighting which best depicts the volume of oval objects, among others also the human face, but this isn’t the only option. Key light can come from any direction, if this direction gives volume to the filmed object in the way we want. For example: from the side – side light.
The goal of the key light is the shadow, which creates the illusion of volume.
The head on the picture is lit by the key light but is seems as though something is missing here. The volume of the face is surely seen but the left side of the head is lost in the dark and the shape is disappearing and merging with the black background.
In some cases, this is the wanted effect but this time we wish to light the picture in a way that the impression of the spatial volume is as whole as possible.
We lighted the situation with another light source, namely from the direction which is opposite to the direction of the camera. This position is called backlight. In film jargon, we often hear the German expression “Gegenlicht”.
The role of the backlight is to make the filmed object distinguishable from the background. Because of the backlight, the left side of the head doesn’t get lost in the dark and its outline is clearly visible.
Seemingly we achieved our goal: the volume of the head is visible and the head is distinguishable from the background. But if we take a look at the shadows on the face, made by the key light, we see that the shadow is unreadable, without details. In a way, it belongs to the background more than to the face itself.
The dark shadow on the face requires additional lighting, so the details in the shadow become visible and recognised as part of the face. This is the role of the fill light or “fill” in the filming jargon.
The role of the fill light is solely the regulation of contrast and in no way the modelling of volume. The fill light shouldn’t form visible shadows. It would be ideal if the fill light would come from the camera lens itself, so that the shadows would stay hidden behind the filmed object. Since this is impossible, the light is set as close as possible to the lens, usually above the lens but from the side, which is opposite to the side of the key light. This light should be as soft as possible to make the potential shadows less visible.
The intensity of the fill light shouldn’t exceed the intensity of the key light.
The head is lit by the key light, back light and fill light. Its volume is clearly expressed and it’s distinguishable from the background. But on a black background, it gives the impression that it is cut out and glued to it. Altogether, something is missing.
This deficiency is corrected by the background light. As opposed to the other three light sources that have more or less specific positions and directions, the background light doesn’t. Its characteristics are defined according to the demands and possibilities of individual, concrete cases.