Methods, devices and systems for quantifying fluorescence and optical properties in a turbid medium such as tissue are disclosed. One of the methods comprises: providing fluorescence emission and reflectance wavelengths detected from a target surface where each of the detected wavelengths is associated with a respective known distance between a respective excitation source giving rise to the respective detected wavelength and a detector detecting the respective detected wavelength； and calculating the optical properties based on the detected wavelengths and the respective known distances. The known distances may be predetermined to enable calculation of a desired range of values for the optical properties. The calculation of the optical properties may be based on a model of light interaction with the turbid medium where the model limits a range of calculated values for the optical properties.
