A light source for a spectroscopy unit that measures tissue includes a block for engaging tissue and a light source. The block is formed of translucent material. The light source is positioned in close proximity to the block either directly or through use of a light fiber. The light source produces light at a single wavelength or small range of wavelengths shorter than the desired range of wavelengths to be produced by the light source for the spectroscopy unit. A luminescent material is placed in the light path between light source and the tissue to produce the desired wavelength of light when pumped by the light source.