Dichroic filters are glass filters that are inserted into the back of theatrical lighting fixtures. These filters come in a variety of colors that produce colored lighting by reflecting the undesired colored lights of the spectrum. They have similar uses to color gel filters. Unlike color gel filters, dichroic filters reflect the light they are not using rather than absorbing it. For this reason, they remain cooler than gel filters. Dichroic filters are made of glass, unlike color gel filters which are made of plastic, and the glass is tinted to various colors in the light spectrum.
Both dichroic filters and color gels can be used to achieve the same results. As both types of filters come in a variety of colors, they can be used for a variety of purposes. For instance, cooler color filters, such as blues and violets, can be placed outside of set windows to simulate night lighting. Similarly, warmer color filters, such as amber and red, can be used to simulate daylight. Additionally, both dichroic filters and color gels can be used for color correction purposes to achieve a white balanced image when theatrical performances are filmed or videotaped.
Though both dichroic filters and color gels are used to achieve the same results in theatrical productions, dichroic filters have specific uses and advantages that color gels do not. For instance, because dichroic filters remain cooler for extended time periods, the filters can be more easily handled after use. Additionally dichroic filters are made of glass with the color intrinsic to the filter, so they last longer than color gels, which can melt, deform and bleach out over time. Due to this, dichroic filters are often used for long-running theatrical productions.
The primary disadvantage of choosing to use dichroic filters for theatrical productions is the higher initial cost to purchase and set up the lighting system. The filters themselves cost much more than the traditional plastic gels and must be used on lights that are equipped for cool beam filters. If the production has a short run, it may be more cost effective to use and replace color gels rather than investing in dichroic filters. Additionally, because dichroic filters are made of glass, they are more fragile than their plastic counterparts, which may prove problematic for touring productions.