Color Temperature Straw

Overview

Color Temperature Straw (CTS) is a conversion or correction filter (light gel) for luminaires in film, TV, and stage productions. It lowers the color temperature of a light source, imparting a warm character to the light. CTS is closely related to the more familiar CTO (Color Temperature Orange) family: both are used to warm up light, but CTS has a more yellow and less red hue. Manufacturers like Rosco describe the Straw series as calibrated to the same correction and transmission values as CTO, but with a yellowish-amber tint.

The filter is stretched in front of the light source (frame, clamps, filter sleeve) and is made on a heat-resistant base material. It is offered in several density levels, from Full to Eighth, allowing the intensity of the warming effect to be controlled.

Gradations and Manufacturer Codes

CTS, like CTO/CTB, is available in four standard densities. The following table lists the codes for the two most common manufacturers, along with the Mired Shift value according to Lee Filters.

A positive Mired Shift indicates a reduction in color temperature (warming). Example values: According to manufacturer specifications, Half CTS converts approximately 6500 K to about 4300 K, and Quarter CTS converts approximately 6500 K to about 5100 K. As with all correction filters, the filter absorbs light. Lee Filters specifies transmission or density for the filters: for Full CTS, approximately 62% transmission (density about 0.21), which roughly corresponds to a loss of about 2/3 to 3/4 of a stop; Half CTS has about 71–74% transmission, meaning about half a stop.

On-Set Usage

Typical applications:

• Warming Daylight: Daylight fixtures (HMI, LED in Daylight mode) are shifted towards Tungsten/evening light to create warmer skin tones or a golden mood.
• Balancing Mixed Lighting: When warm practical lights or Tungsten sources are present in the frame, a cool source can be subtly balanced with CTS.
• Graduated Correction: The four densities allow for fine-tuning the warming effect without changing the light source.

The practical difference from CTO lies in the color tone: CTS appears more yellow and less red/orange than CTO. The choice between these two families is often an aesthetic decision by the camera department. CTS, like CTO, is the warming counterpart to CTB (Color Temperature Blue), which cools the light.