As noted from Figs. 1 and 2, only white LED lamp and LED monitor as ambient illumination sources do not obviously interfere with the Raman measurements. However, these commercially available white LED-based light sources also have weak and smooth emissions in the NIR region as shown in Fig. 1. Therefore, a broad band-pass filter has to be used so that the visible light can be transmitted while the NIR emissions can be blocked. The long-pass filter in the signal collection path also has to be carefully designed so that the visible light can be rejected. Figure 3 shows the transmission properties of the multiple-filtering system, including the broad band-pass filter, the long-pass filter, and the narrow band-pass laser-line filter. The broad band-pass filter (FSR-BG39, Newport, California), placed in the LED light source, passes through all the visible light and blocks all the NIR light that is longer than 700 nm for illumination. The long-pass filter (BLP01-785R-25, Semrock, New York), placed in the Raman signal collection path, blocks all the visible light and NIR light that is less than 785 nm, and passes through all the NIR light that is longer than 785 nm for the Raman spectrum measurement. Otherwise the visible component entering the spectrometer may generate second-order signals that will also interfere with the Raman signals. The narrow band-pass laser-line filter (LL01-785-12.5, Semrock, New York), placed in the Raman excitation path suppresses the laser side bands and emissions from within the fiber.