Dichroic filters are durable glass color filters that transmit only certain wavelengths of light, reflecting the rest of the spectrum, rather than absorbing it. Since virtually no energy is absorbed by the filter, light transmission is significantly higher than traditional gels and will never burn out or fade.
The gel equivalent to Rosco's "1/2 Blue CTB" Dichroic Filter is E-Colour 202.
Rosco Cinedichro™ CTO and CTB dichroic filters have been engineered to provide true, accurate color correction, precisely matching industry standards for color balancing daylight and tungsten light sources. Relying on the filters ability to withstand extremely high temperatures, Cinedichro™ filters can be used on most motion pictures lighting fixtures - even 6K pars.
Permacolor filters are manufactured in five standard sizes on durable borafloat glass 1.75mm (.069") thick or can be custom cut in any size up to 13.5" in diameter.