Near-infrared light can penetrate skin and tissue readily while absorbed by hemoglobin and oxyhemoglobin at different wavelengths. Thus, a spectrophometric method can be employed for quantification of organ oxygenation. A study of the optical transmission of different wavelengths of light through the brain/skull interface to assess brain oxygenation and blood flow is presented. The optical absorbance was shown to increase with blood oxygenation at 700 nm. The wavelength of 700 nm detects deoxygenated hemoglobin since its absorption is greatest at lower levels of oxygenation. The wavelength of 880 nm detects oxygenated hemoglobin since its absorption is greatest at higher levels of oxygenation. The wavelength of 805 nm is the isobestic point, which is the wavelength where the oxygenated and deoxygenated hemoglobin absorption curves cross. This wavelength can be used as the reference, since the absorption level should not change for the different levels of blood oxygenation.