Abstract: Surface roughness measurements are made by illuminating a surface with coherent light to generate a speckle pattern and studying characteristics of the speckle pattern. The disclosed techniques may be applied to measuring the surface roughness of skin or other biological surfaces. Skin roughness information may be used in the diagnosis of conditions such as malignant melanoma. Methods and apparatus for measuring the coherence length of optical sources involve extracting information about speckle patterns resulting when light from the optical sources interacts with a surface having a known roughness.