Energy meters and optical power meters are optical testing instruments.  Power meters are optical testing instruments designed to measure the average power of a continuous light beam. The instrument is used frequently to measure the beam power of continuous wave lasers. Energy meters are optical testing instruments designed to measure the total energy of a single pulse. The instrument is used frequently to measure the beam energy of pulsed lasers.  Energy meters and optical power meters can be supplied as combination test meters.  Important specifications to consider include wavelength range and sensor diameter.  The wavelength range is the range of wavelengths the detector is designed to test over.  The sensor diameter is the diameter of the active sensor area.