The Type 1501-A Light Meter gives a reading of the total amount of light falling on a phototube through an aperture at the front of the meter. Its primary use is in photography with electric flash tubes of the xenon type (called “Speed- lights”, “Strob”, etc.) to determine the correct camera aperture for color-film exposure.* The General Radio Light Meter differs from ordinary “exposure” meters in that it is designed to sum up and indicate the total amount of light in a short flash, rather than to indicate the average level of continuous illumination. This meter is also particularly useful in making periodic checks of electric flash tubes used in speedlights to be sure that they have not deteriorated to the point where tube replacement or servicing is desirable. A further use is in comparing the illumination produced by different xenon flash tubes. It is possible to use the meter on other types of flash units and the common combustible flash bulb, if allowance is made for the difference in spectral distribution of the emitted light. For measuring the intensity of light reaching the film in the camera, an accessory probe (Type 1501-PI) is available which attaches to the back of the camera ground glass with rubber suction cups. A plate (Type 1501-P2) for mounting a standard Eastman or Wollensack synchronized shutter is also available for testing combustible flash bulbs.