Last Updated 5 days ago
Filmmaking Dictionary: Letter C / CTO (Color Temperature Orange)
Definition
CTO (Color Temperature Orange) is an orange colour-correction filter used to shift a light toward a lower colour temperature. It is commonly used to bring a daylight source closer to tungsten balance or to add deliberate warmth.
The result depends on the source spectrum, filter and camera white balance. CTO can help match sources, but it does not automatically create natural skin tones or remove every colour difference between fixtures.
Full, Half and Eighth CTO
CTO is sold in several correction grades. The fractions describe filter strengths within a range, not fixed Kelvin subtractions or fixed amounts of exposure loss.
- Full CTO: a stronger warming conversion. LEE 204, for example, is specified for a nominal 6500K source to approximately 3200K.
- Half CTO: an intermediate grade for less warming; its exact result depends on the product and starting source.
- Eighth CTO: a lighter warming grade when a smaller adjustment is required.
Do not apply one manufacturer’s conversion figures to every gel sold under the same strength name. Read the specified starting conditions and compare the result on camera.
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Quarter CTO
Quarter CTO, written ¼ CTO, is a relatively light orange correction grade. It gives a smaller warm shift than full CTO in the same range. A gaffer might use it to bring a source closer to a warm practical or to make a selected light slightly warmer than the rest of the scene.
LEE 206 Quarter CTO has a specified mired shift of +64 and is described for a nominal 6500K source to approximately 4600K. It therefore does not perform a full daylight-to-3200K conversion in that example.
The same filter on a different starting source gives a different result. Quarter CTO is not “one quarter of 5600K,” nor does its name mean that it removes a quarter stop of light.
Matching and Creative Warmth
If a scene is balanced around tungsten practicals, CTO can reduce the difference between those practicals and a daylight source. Correct only as far as the scene needs: mixed colour temperatures can be a deliberate part of the look.
A small warming adjustment on a face is a creative choice, not a universal improvement. Check the actor, makeup, wardrobe and background together under the intended camera settings.
Keep the practical lamp’s actual colour in mind. Household lamps are not all 3200K, and different LED bulbs can have different spectra even when their packaging lists the same colour temperature.
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Practical Checks
- Compare the gelled and un-gelled source at a fixed camera white balance.
- Account for the filter’s light loss when setting exposure.
- Keep gel clear of hot surfaces using the fixture’s approved mounting arrangement.
- Record the product number and strength for matching coverage or later pickups.
- Use separate green–magenta correction when needed; CTO is not a universal colour repair.
With a tunable LED, changing the fixture’s colour-temperature setting may be preferable to adding a filter. Test the result rather than assuming the displayed number guarantees a match.
CTO Versus CTB
CTO warms a source relative to a fixed camera white balance. CTB cools it. Diffusion changes light distribution, while neutral-density material primarily reduces output. These are different jobs even when filters are combined in one setup.
Learn more in the lighting department guide.
Related Terms
- CTB (Color Temperature Blue)
- Color Temperature
- Practical
- Diffusion
- Gel / Gels
- Fractional Diffusion, Gel and Filter Strengths
Browse terms beginning with C or return to the filmmaking dictionary.