Total Reflection X-Ray Fluorescence Analysis (TXRF) has been proved to be well suited for the energy dispersive analysis of light elements using a special spectrometer, which is equipped with an energy dispersive detector having all properties for the detection of low energy radiation. The detection of the light elements is strongly influenced by the excitation source which should provide a large number of photons with energies near the K-absorption edge of these elements (0.2 - 3 keV). Various standard tubes with Be-window as well as a homemade windowless tube are compared, all differing in focal size, total power and anode material. Optimized excitation conditions are provided by synchrotron radiation meeting all requirements for excellent excitation of light elements in total reflection geometry such as high brilliance and ideal spectral distribution specially in the low energy region. A comparison of excitation with X-ray tubes as well as with synchrotron radiation is shown. Detection limits of 200 fg for Mg have been obtained with synchrotron radiation.