“ Designing With
Dichroics “
Page One
Our Definition Of A Dichroic Filter: An optical coating that is designed to reflect and transmit a specific band of frequencies in conjunction with a predetermined angle of incidence to the source.
Dichroic filters are manufactured with the latest in state of the art technology. Dichroic filters have many features that are not available in most color mediums such as higher transmission in ultra-chromatic colors, higher tolerance to infrared energy, less then 4% absorption and longer life.
When considering your choice of color media, you must ask yourself some basic questions about the application. The answers to these questions will help you decide which color media will best suit your needs especially since you now have at least four different color mediums to select from: gel/polyester, stained glass, Lexan and dichroic, all of which have a place in lighting. The problem is deciding which one is right for you.
A dichroic filter is composed of dielectric materials which are deposited on the surface of a boroscilicate substrate (glass). The substrate will break down before the coating and therefore, the thermal information measured from the mounting area is required to ensure the use of a proper substrate.
There are many variables to consider when introducing glass to heat in a restricted environment. These variables will be listed later. The standard substrate used for dichroic filters is a low expansion boroscilicate (borofloat) approximately 1.75mm - 4mm thick with an expansion coefficient of 33. This substrate will tolerate temperatures up to 450 degrees Celsius for several hours when properly installed however, there is a temperature differential tolerance that must be adhered to to prevent a thermal fracture (COE) coefficient of expansion. The COE varies for each type of substrate. Other substrates are available for coatings such as fused-silica (quartz). Additional charges may be incurred to offset the cost difference of the materials used and any tooling that may be required.
Thin Film Coating: There are several ways to create a thin film optical coating . The most popular for creating a dichroic color filter is E Beam Evaporation, also known as electron bombardment or physical vapor deposition (PVD). Other processes for creating a thin film optical coating are sputtering and chemical vapor deposition (CVD). Each of these processes have advantages and disadvantages which are determined by the application the coating will be exposed to.
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