A spectrometer for measuring information from sample material moving at a distance, the spectrometer comprising: a) a broad band light source for delivering irradiance to a small area on moving sample material at a distance; b) a first optical device implemented in between the sample and a hollow light guide for collecting back reflected, scattered or transmitted radiation flux from the sample at a distance, the first optical device being implemented by a reflective element or system of elements, c) a hollow light guide with an input end and an exit end having a rectangular internal cross section for maximizing spatial filtering and for minimizing subsequent coupling losses from a rectangular exit end of the hollow light guide to a linear detector array receiving back reflected, scattered or transmitted broadband radiation from the sample to the input end and homogenising this broadband radiation spatially to the exit end after multiple reflections inside the hollow light guide, wherein the first optical device images the received radiation into the hollow light guide; d) a second optical device implemented by a reflective element or system of elements in between the hollow light guide and a sensor module for imaging and magnifying the radiance present at the exit end of the hollow light guide into the sensor module; e) a linear variable filter receiving spatially homogenised radiation from the exit end of the hollow light guide for splitting the broadband radiation into wavelength components; f) the linear detector array for converting optical radiation into measurable electrical signals, wherein each pixel of the array receives different wavelength components; g) means for processing electrical signals from the pixels into spectral information; and h) the sensor module containing the linear variable filter, the linear detector array and means for cooling and stabilizing the operating temperature of both the linear detector array and the linear variable filter, while the spectrometer is operating in variable environmental conditions. a) a broad band light source for delivering irradiance to a small area on moving sample material at a distance; b) a first optical device implemented in between the sample and a hollow light guide for collecting back reflected, scattered or transmitted radiation flux from the sample at a distance, the first optical device being implemented by a reflective element or system of elements, c) a hollow light guide with an input end and an exit end having a rectangular internal cross section for maximizing spatial filtering and for minimizing subsequent coupling losses from a rectangular exit end of the hollow light guide to a linear detector array receiving back reflected, scattered or transmitted broadband radiation from the sample to the input end and homogenising this broadband radiation spatially to the exit end after multiple reflections inside the hollow light guide, wherein the first optical device images the received radiation into the hollow light guide; d) a second optical device implemented by a reflective element or system of elements in between the hollow light guide and a sensor module for imaging and magnifying the radiance present at the exit end of the hollow light guide into the sensor module; e) a linear variable filter receiving spatially homogenised radiation from the exit end of the hollow light guide for splitting the broadband radiation into wavelength components; f) the linear detector array for converting optical radiation into measurable electrical signals, wherein each pixel of the array receives different wavelength components; g) means for processing electrical signals from the pixels into spectral information; and h) the sensor module containing the linear variable filter, the linear detector array and means for cooling and stabilizing the operating temperature of both the linear detector array and the linear variable filter, while the spectrometer is operating in variable environmental conditions.