Systems and methods are disclosed for non-invasively measuring blood glucose levels in a biological sample based on spectral data. This includes at least one light source configured to strike a target area of a sample, at least one light detector, which includes a preamplifier having a feedback resistor, positioned to receive light from the at least one light source and to generate an output signal, having a time dependent current, which is indicative of the power of light detected, and a processor configured to receive the output signal from the at least one light detector and based on the received output signal, calculate the attenuance attributable to blood in a sample present in the target area and eliminate effect of uncertainty caused by temperature dependent detector response of the at least one light detector, and based on the calculated attenuance, determine a blood glucose level associated with a sample.
