Filter
(1) Improve Contrast
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The phosphor that is display segment in VFD is almost white. If the light from the outside shines the phosphor, the contrast between on and off segment gets worse. The optical filter avoids the reflective light on the phosphor to improve contrast and readability. And also, it has an effect that the structure inside of VFD is difficult to be seen. The transmissivity of the optical filter is generally used 20～40% in commercial application, 5～20% in car application.
(2) Color Modulation
The color of light can be changed through the optical filter. Some examples are shown below.
A) Changing the Color
The color green is high luminous and has a wide spectrum. It gets appropriate color from blue to red combined with various optical filter. Pink filter (color is almost wine red) can turn the color to white. The various colors of phosphor have been developed. Used red or blue with main color green, the optical filter of color close to red is difficult to transmit the blue light. The blue light is hard to be seen because of the characteristic of the filter.
B) Improvement of Color purity
By using same color filter as luminous light make the color more vivid.
(3) Guard the VFD
VFD is weak to a high pressure and a shock, since VFD is made of glass. It needs a guard cover. The optical filter is used both as improvement of set appearance and as improvement of contrast. So that the filter of commercial equipment like audio and video set is made of semitransparent plastics like acrylic resin. In case of using filter in practice, please consult with filter manufacturer and confirm the real one carefully.