Multiple-color light-emitting diodes (LEDs) were used for photoacoustic (PA) imaging of printed color specimens, and the obtained PA images agreed well with the corresponding amount of absorbance of the specimens. The LED light sources with wavelengths of 455, 505, 617, and 660 nm were used to evaluate PA images that were obtained for colored specimens printed on the front and rear surfaces of an OHP sheet. The PA images obtained for individual wavelengths were combined to recover the colored image of the specimen, and the recovered image was compared with the original full-color image. The PA signals with amplitudes and phases behave as vectors so that the vectorial addition of PA signals generated from the surface and undersurface well describes the PA signal behavior. Furthermore, imaging of a layered specimen with a surface color layer was also carried out, which lead to successful thermal depth profiling with a colored optical source.

A low-price handy-size spectrometer was designed and fabricated. Wavelength scanning was achieved by switching LEDs with eight wavelengths. The obtained transmission spectra agreed well those obtained with a conventional spectrometer with the correlation coefficients up to 0.9985 − 0.9999. The LED spectrometer was applied to measure a time-varying chemical reaction such as neutralization titration. It was applied to a first-year natural science fundamental education. The evaluation from the students showed the usefulness of the present apparatus for the engineering basic education.