RAE Systems photoionization detectors (PIDs) currently offer lamps with three different photon energies: 9.8 eV, 10.6 eV and 11.7 eV. A special high-intensity version of the 10.6 eV lamp is also available for use with ppbRAE Plus. Instruments are shipped with the standard 10.6 eV lamp unless otherwise specified. The 11.7 eV lamp measures the broadest range of compounds, while the 10.6 eV lamp is somewhat more selective, and the 9.8 eV lamp is the most selective. Because of the different type of lamp window needed to allow the higher energy light to pass, the 11.7 eV lamp has a shorter life (see table) and is more expensive. Therefore RAE Systems recommends using the 9.8 or 10.6 eV lamps whenever possible.