Production Lighting: How To Use Fill for Key
Video production lighting is an extremely important part of cinematography. Great lighting can make a $100,000 movie look like it cost $1,000,000 to shoot while poor lighting can lower your production's value. When you design your lighting for a scene it's important to understand the functions of your lights.
Know Your Lights
The key light is the brightest light. The key light is the first light to be set and it is the brightest one on set, hence the name key light. Because it is the brightest light it will cause the most shadows. You need to position your other lights in accordance with this so that your image does not suffer from the double shadow phenomenon that plagues poor lighting set ups.
The next light to set up is for your subject is called the fill light. It can either be a smaller light or a bounce board. Its purpose it to balance out the shadows created by the key light. The fill light fills in dark areas.
After the key and fill you have the back light. This light creates a halo around the subject and helps pop them out of the background. After that you have lights placed in the background called specials. This lights light up individual background stuff and help add more dimension to your depth of field.
Using Fill for Key
It is confusing and inaccurate to say you are substituting a fill light for a key light because your key light is, by definition, the biggest light. If you normally use a 650 watt light for fill and then choose to make it the key light then it is now a key light instead of a fill light. But, if you were to add a 2,000 watt light into the mix then that would become your new key light because it overpowers the 650 watt light.
What this phrase most likely refers to is using the bounce card as a key light. Bounce card, which could be a white piece of bead board or foam core, is sometimes called fill card. When you bounce a light into it and redirect the bounce onto the subject it gives off a very even and soft light. We usually use this for fill by bouncing some of the light that spills from the key back onto the subject. But it is possible to use bounce card as a key light as well.
Lighting with Bounce Card
Its easy to use the bounce card that your normally use for fill as your key light. All you need to do is block your subject. Then you need to set a light and your card. Position the card and the light so that the light bounces into the card and that light bounces back onto the subject. Once you have found a good position for the bounce card use a stand with a clamp to hold it in place.
Something you normally use as a fill is now your key light.