Compact multi-wavelength light sources have been developed to provide flexibility in pulse oximeter device design. Advantages of these light sources include emitting light of multiple wavelengths with a constant ratio of intensity, and a co-linear light propagation path through tissue. These devices can function as normal pulse oximeter to determine oxygen saturation and pulse rate, but this approach potentially reduces circuit complexity, reduces motion artifacts and enables multi-wavelength sensing of different forms of hemoglobin or other blood products.