Glass-ceramics fo a light filter capable of preventing variation of refractive index in a band-pass filter have a coefficient of thermal expansion within a range from 95.times.10.sup.-7 /.degree.C. to 140.times.10.sup.-7 /.degree.C. within a temperature range from -20.degree. C. to +70.degree. C. and, preferably, Young's modulus of 85 GPa and bending strength of 10 kg/mm.sup.2, and light transmittance for plate thickness of 10 mm of 60% or over within a wavelength range from 950 nm to 1600 nm. Predominant crystal phases of these glass-ceramics should preferably be (a) lithium disilicate and (b) one selected from the group consisting of .alpha.-quartz, .alpha.-quartz solid solution, .alpha.-cristobalite and .alpha.-cristobalite solid solution.

el fo de la Cristal-cera'mica un filtro ligero capaz de prevenir la variación del índice de refracción en un filtro band-pass tiene un coeficiente de extensión termal dentro de una gama de 95.times.10.sup.-7 /.degree.C. a 140.times.10.sup.-7 /.degree.C. dentro de una gama de temperaturas de -20.degree. C. a +70.degree. C. y, preferiblemente, módulo de Young de 85 GPa y de la resistencia de flexión de 10 kg/mm.sup.2, y transmittance ligero para el grueso de la placa de 10 milímetros de el 60% o del excedente dentro de una gama de longitud de onda a partir del 950 nm a nm 1600. Las fases cristalinas predominantes de estos la cristal-cera'mica debe preferiblemente ser (a) el disilicate y (b) uno del litio seleccionado de la solución sólida del alpha.-cuarzo del grupo que consiste en, de la solución del alpha.-cuarzo, del alpha.-cristobalite y del sólido del alpha.-cristobalite.

 
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