When talking about light, intensity is the power per unit area when the light is transmitted through a (real or imaginary) flat surface that is perpendicular to the direction of the beam. It is usually represented by the symbol I and common units are W/m2 or W/cm2. At StellarNet this is also called Irradiance and many of our systems can be calibrated for spectral irradiance over the wavelength range of your spectrometer. For example, if a laser beam is circular with a radius of 1 mm and has a power of 100 mW, the intensity is:
A StellarNet NIST Traceable Irradiance calibration service or IRRAD-CAL can be purchased with most spectrometer configurations to allow for this type of measurement. Spectrometers will also need a light collecting accessory (CR2, IC2, IS6, or IS12) and usually an optical fiber.
