A wafer inspection system includes a laser sustained plasma (LSP) light source that generates light with sufficient radiance to enable bright field inspection. Reliability of the LSP light source is improved by introducing an amount of water into the bulb containing the gas mixture that generates the plasma. Radiation generated by the plasma includes substantial radiance in a wavelength range below approximately 190 nanometers that causes damage to the materials used to construct the bulb. The water vapor acts as an absorber of radiation generated by the plasma in the wavelength range that causes damage. In some examples, a predetermined amount of water is introduced into the bulb to provide sufficient absorption. In some other examples, the temperature of a portion of the bulb containing an amount of condensed water is regulate to produce the desired partial pressure of water in the bulb.