Color correction filter with +131 Mired shift for complete tungsten-to-daylight conversion. Lee #201 absorbs red spectrum with 36% transmission (1.8 stop loss).
Technical Details
Full CTB reduces light intensity by approximately 1.8 stops with a transmission of 36%. The filter consists of dyed polycarbonate or polyester film in standard thicknesses of 0.13mm (LEE 200) or 0.25mm for more robust use. Spectral absorption occurs mainly in the red range between 600-700nm. Available variations include 1/2 CTB (half correction, 81 Mired), 1/4 CTB (38 Mired), and 1/8 CTB (19 Mired) for finer gradations.
History & Development
Eastman Kodak developed CTB filters in the 1930s for color film photography, when artificial light and daylight films were first distinguished. Lee Filters standardized today's numbering in 1971 with LEE 200 for Full CTB. While the introduction of LED luminaires from 2010 onwards reduced the need for physical filters, CTB gels remain indispensable for tungsten-halogen lights and practical light sources.
Practical Use in Film
Roger Deakins extensively used Full CTB in "Blade Runner 2049" (2017) to match tungsten lights to the cool daylight ambient mood. A typical workflow: tungsten Fresnel luminaires are fitted with CTB filter frames to simulate daylight entering through windows. The light loss of 1.8 stops requires correspondingly stronger luminaires – a 2K tungsten effectively becomes a 650W equivalent. CTB is particularly suitable for mixed lighting situations where artificial and natural light must be present in the frame.
Comparison & Alternatives
Unlike CTO (Color Temperature Orange), which converts daylight to tungsten, CTB works in the opposite direction. Modern LED panels with adjustable color temperature are increasingly replacing filtered tungsten lights, but often offer lower light output. HMI luminaires already produce daylight-like 5600K and therefore do not require CTB. For extreme color temperature shifts beyond 5600K, special "Steel Blue" or "Glacier Blue" filters are used.