Abstract: Glass-ceramics for 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 95×10−7/°C. to 140×10−7/°C. within a temperature range from −20° C. to +70° C. and, preferably, Young's modulus of 85 GPa and bending strength of 10 kg/mm2, 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 &agr;-quartz, &agr;-quartz solid solution, &agr;-cristobalite and &agr;-cristobalite solid solution.

Abstract: 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 95×10−7/°C. to 140×10−7/°C. within a temperature range from −20° C. to +70° C. and, preferably, Young's modulus of 85 GPa and bending strength of 10 kg/mm2, 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 &agr;-quartz, &agr;-quartz solid solution, &agr;-cristobalite and &agr;-cristobalite solid solution.

Abstract: Glass-ceramics for 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 95×10−7/°C. to 140×10−7/°C. within a temperature range from −20° C. to +70° C. and, preferably, Young's modulus of 85 GPa and bending strength of 10 kg/mm2, 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 &agr;-quartz, &agr;-quartz solid solution, &agr;-cristobalite and &agr;-cristobalite solid solution.

Abstract: 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 95×10−7/° C. to 140×10−7/° C. within a temperature range from −20° C. to +70° C. and, preferably, Young's modulus of 85 GPa and bending strength of 10 kg/mm2, 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 &agr;-quartz, &agr;-quartz solid solution, &agr;-cristobalite and &agr;-cristobalite solid solution.

Abstract: Glass-ceramics of 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 95×10−7/° C. to 140×10−7/° C. within a temperature range from −20° C. to +70° C. and, preferably, Young's modulus of 85 GPa and bending strength of 10 kg/mm2, 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 &agr;-quartz, &agr;-quartz solid solution, &agr;-cristobalite and &agr;-cristobalite solid solution.