A method for detecting air bubbles in a blood flow path using at least one light emitter to generate different wavelengths and at least one photosensor , the method comprising: setting initial intensities of light at a first wavelength emanating from the at least one light emitter and of light at a second wavelength emanating from the at least one light emitter ; determining intensities of the light at the first wavelength and of the light at the second wavelength received at the at least one photosensor , wherein the light at the first wavelength and the light at the second wavelength received at the at least one photosensor traverses the blood flow path ; determining a normalized ratio between an absorbance for the light at the first wavelength and an absorbance for the light at the second wavelength using the initial intensities of the light at the first wavelength and of the light at the second wavelength emanating from the at least one light emitter and the intensities of the light at the first wavelength and of the light at the second wavelength received at the at least one photosensor , wherein the absorbance for the light at the first wavelength is obtained by subtracting the intensity of the light at the first wavelength at the at least one photosensor from the initial intensity of the light at the first wavelength emanating from the at least one light emitter , and wherein the absorbance for the light at the second wavelength is obtained by subtracting the intensity of the light at the second wavelength at the at least one photosensor from the initial intensity of the light at the second wavelength emanating from the at least one light emitter ; and determining whether an air bubble is present in the blood flow path based on the determined normalized ratio by determining a change in the normalized ratio and a normalized ratio at a previous time period, wherein the air bubble is present if the change meets or exceeds a predetermined threshold. setting initial intensities of light at a first wavelength emanating from the at least one light emitter and of light at a second wavelength emanating from the at least one light emitter ; determining intensities of the light at the first wavelength and of the light at the second wavelength received at the at least one photosensor , wherein the light at the first wavelength and the light at the second wavelength received at the at least one photosensor traverses the blood flow path ; determining a normalized ratio between an absorbance for the light at the first wavelength and an absorbance for the light at the second wavelength using the initial intensities of the light at the first wavelength and of the light at the second wavelength emanating from the at least one light emitter and the intensities of the light at the first wavelength and of the light at the second wavelength received at the at least one photosensor , wherein the absorbance for the light at the first wavelength is obtained by subtracting the intensity of the light at the first wavelength at the at least one photosensor from the initial intensity of the light at the first wavelength emanating from the at least one light emitter , and wherein the absorbance for the light at the second wavelength is obtained by subtracting the intensity of the light at the second wavelength at the at least one photosensor from the initial intensity of the light at the second wavelength emanating from the at least one light emitter ; and determining whether an air bubble is present in the blood flow path based on the determined normalized ratio by determining a change in the normalized ratio and a normalized ratio at a previous time period, wherein the air bubble is present if the change meets or exceeds a predetermined threshold. <EOS>