Diffuse transmittance visible spectroscopy using smartphone flashlight for photoplethysmography and vital signs measurements

[Display omitted] •Novel smartphone flashlight based diffuse transmittance spectroscopic approach for vital signs detection.•Noise free and accurate measurement of photoplethysmography and oxygen saturation using smartphone flashlight.•Simple forward model for the diffuse transmittance spectra for different levels of SpO2 verified by experimental measurements.•Orange and red wavelengths, 610–635 nm, are associated with blood oxygen saturation levels.•Potential application of dynamic spectral measurement of physiological parameters with integrated smartphone platforms. Photoplethysmography (PPG), with its wide range of applications, has become one of the most promising modalities for healthcare monitoring technology. In this work, we present a new PPG measurement technique based on diffuse transmittance spectroscopy (DTS) with the help of a smartphone built-in flashlight as an alternative broadband light source. The blood Volume Pulse (BVP) signal was extracted from recorded transmittance spectra at 620 nm. The results were compared with the ground truth and conventional contact finger PPG sensors. A very high correlation was found between the diffuse transmittance signal and the reference PPG signals (r = 0.997, p