Broad spectrum InGaAsP/InP light emitting heterostructures were grown by low temperature liquid phase epitaxy (LPE). The structure of the LED wafers was investigated by optical transmission measurements, and the layer thicknesses were also measured by electron microscopy. Two quaternary light emitting layers of different composition were built in one device structure in order to broaden the usable wavelength range of the emission spectrum. One of the layers is electrically, whereas the other is optically excited as a result of internal absorption and re-emission of the LED light. As a result of this absorption and re-emission process the modified LED chips have substantially broader emission spectra and higher radiance than the conventional surface emitting multi-wavelength NIR LED structures. The two emission peaks of the spectrum were designed for matching the first and second harmonic wavelength of the fundamental absorption band of C-H bonds. The internal quantum efficiency of the wavelength conversion in this type of LEDs is nearly 100%.