An instrument for measuring laser energy in the visible range and which determines when the optical energy exceeds the accessible emission limit for a Class I laser. The instrument employs a photoelectric detector and a filter for a range of 476 to 633 nm. The instrument measures the optical energy as a function of time and compares the measured value with the accessible emission limit for a Class I laser at various critical points in time. A 3-digit engineering-notation display format is used to output the computed time at which the laser energy exceeds the Class I limit, as well as the total energy measured in 10 seconds. The instrument is adapted to measure either CW laser radiation, pulsed laser radiation, or each pulse of laser radiation, computes and applies a correction factor for optical error conditions or variations between optical detectors, and measures and compensates for background energy. Mode and scale information, and sensed data, are read into a micro computer and are read out on a LCD display.