Importance

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Abstract

High purity (95-99.5 percent) red, orange and yellow filters are disclosed which comprise a periodic stack of relatively low index of refraction dielectric material (L) such as SiO.sub.2 or MgF.sub.2 and absorbing relatively high index material such as silicon or Fe.sub.2 O.sub.3. Together, the low and high index materials provide a high index ratio (typically 1.7 to 2.5). The filters are fabricated according to designs such as (H/2 L H/2).sup.n, typically using only 5 to 7 layers. Despite the very small layer count, these filters provide overall optical performance which is at least the equivalent of all-dielectric filters of 30 or more layers, with color purity that is unachievable by all-dielectric filters and simple low cost design. In addition, our filters have inherently low stress levels and absorb and reflect unwanted light such as blue light. As a consequence, the filters are ideally suited for coating on flexible substrates such as plastics and for coating on lamp envelopes to form red or yellow bulbs which are ideally suited, for example, for use as automobile tail light bulbs, side marker bulbs and turn signal bulbs.

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First Claim