The letter

One letter a week, starting soon.

The week's signal, what the makers shipped and what the reviewers found, and the editor's note. No tracking, no ads, nothing else.

We keep your address, your language and the date you joined, nothing else. Every letter has a one-click unsubscribe link that deletes the record.
Cinematography3 min read

LESSON 103

Mixing colour temperatures

Warm lamps, cool windows, one frame.

IN THIS LESSON

  1. The problem
  2. Correcting with gels
  3. Mixing on purpose
  4. Practice: a working approach

The problem

Many real locations mix light of different colours: blue daylight from a window, orange tungsten bulbs in the room, greenish fluorescent tubes overhead. A camera can only be balanced for one white at a time, so in a mixed room some sources will look wrong. Daylight sits around 5500 to 6500 kelvin and tungsten around 3200 kelvin, a large gap. Fluorescent lamps also tend to add a green tint that sits on a separate green to magenta axis from the warm to cool scale.

Correcting with gels

Colour gels are thin sheets of heat-resistant plastic, today polycarbonate or polyester, placed in front of a light to colour it or correct it. To match sources, a common method is to put correction gels over each light so they all share one colour temperature. A bluish filter or gel converts warm tungsten light toward daylight, and an orange one warms daylight toward tungsten. Fixtures with discharge lamps are sometimes fitted with gels to imitate tungsten. Gels fade over time, especially deep colours and blues, and must be replaced.

Mixing on purpose

Mixed colour is not always a fault. Gels can also simulate the natural mix of temperatures found in real places, and colour can carry mood: warm tones can suggest comfort or passion, cool tones sadness or isolation. A cool moonlit window against a warm lamp is a classic night look. The choice is whether the mix is controlled and intended, or random and distracting. Faces are the test, because viewers notice odd skin colour long before they notice an odd wall.

Practice: a working approach

This is working practice. Decide which source is the key and balance the camera to it. Then make the others match it, or push them deliberately warmer or cooler. Turn off overhead fluorescents if you can, or gel them with a minus-green gel. Modern LED panels often let you dial kelvin and tint directly, which is the fastest fix. Check skin on a vectorscope or a monitor you trust, not just by eye. Then lock the camera's white balance so it cannot drift while you work.

Try it today

  1. 01Find a room with a window and a tungsten lamp.
  2. 02Film a face lit by both with camera white balance at 5600 K.
  3. 03Repeat at 3200 K and compare the two sides of the face.
  4. 04If you have a gel or a tunable LED, make the lamp match the window.
  5. 05Then try the opposite: make the mix stronger on purpose.