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3 Main Functions of Light

written by: •edited by: Rhonda Callow•updated: 10/6/2009

Before shooting your video, it helps to consider the three main functions or purposes of light.

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    3 Main Functions of Light

    Whether you realize it or not, lighting does have three major functions that have a great impact on the entire shot. These functions, along with the light source placement(s), intensity and lighting ratio between the light sources, are automatically applied every time a subject(s) is lit. All three functions work hand in hand with one another as well. The three functions of light are as follows: used to cast a shadow, to create separation between subject and background, and light is used to fill in shadows.

    Cast a Shadow

    Sure, you’re using light to light a subject, but have you thought about using light to cast a shadow? When you light a subject, you automatically create a shadow(s). It’s not exactly the light that determines the shape of the subject, but the shadow(s) the subject creates. In addition, the intensity of the shadows will create depth and texture within your subjects and shot, depending on the type of light source and placement of course.

    On most films and television shows, notice how there are various shades of light as well as various shades of shadows; even black and white films have various contrasts of shades between the lights and shadows. Shadows also are used to create the mood. The more intense the light, the more dramatic and harsher the shadow(s), thus the more dramatic the mood.

    Create Separation Between Backgrounds

    When you light your subject, the background will automatically draw in less attention (considering the background isn’t overexposed or overly lit). This separates your subject from the background, creating a three dimensional look in a two dimensional screen. Backlighting your subject in the foreground also helps creates this effect. For, when you have a backlight behind your subject, the light highlights the edges of the subject, automatically creating a separation of space between the foreground and background within the shot.

    Fill in Shadows

    If you don’t want a too dramatic look or mood, you want to use light to fill in the shadows you’ve created. Filling in shadows may be used with a bounce card, reflector, etc., or with another light source. When you fill in the shadows, consider the lighting ratio of the look you’re wanting. (Remember the relation between the key and fill light sources equals the lighting ratio; plus, the less fill you use, the more dramatic the look and/or mood). The fill light source shouldn’t be brighter than the key. You don’t want to introduce more shadows. Therefore, the fill light should be a softer light source, used to soften the shadows created by the key light.