Systems and methods are described for measuring a tissue parameter such as % StO2 in a tissue sample. One such method includes receiving first and second scattered light intensity signals at unique locations on a selected region of tissue from light injected into the region of tissue from a light source to identify a measured light attenuation data value. An electronic data store can be accessed that includes simulated light attenuation data determined from a mathematical tissue model at discrete points over a range of two or more tissue parameters, where the simulated light attenuation data are a function of one or more temperature-dependent light source spectra. The tissue parameter in the tissue sample can be determined by selecting a closest match between the measured light attenuation data and the simulated light attenuation data. An electronic signal representative of the determined tissue parameter can be sent to an output register.