Rosco Permacolor Dichroic FiltersRosco Permacolor 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. Rosco
Permacolor filters are made with the highest quality coatings, designed not to fade or shift color. In addition, Rosco's sophisticated manufacturing process allows for precise color consistency batch to batch to a degree that is unprecedented in other dichroic coatings. 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.Understanding Dichroic Filters
In conventional filters, white light is passed through the filter. The filter selectively absorbs portions of the light spectrum, and allows the remaining slice of the spectrum to pass through. So a blue filter, Roscolux 68 for example, absorbs red and green light, while passing or transmitting the blue.
Dichroic filters work in a similar way. However, the significant difference is that dichroic filters selectively reflect the unwanted portion of the spectrum, passing the desired color. Since the unwanted energy is reflected rather than absorbed into the filter as heat energy, a dichroic filter does not fade or burn out
. In fact, the color does not degrade. And since selective parts of the spectrum are either entirely reflected or entirely transmitted through the filter, the light transmitted is exceedingly pure and saturated. One advantage of this is that dark, saturated colors in gel often have very low transmission, sometimes as low as 5%. A similar color in dichroic might have as much as a 50% transmission of light.