Speed of Light Meter @230V The speed of light can be calculated from this difference and the distance to the triple-prism reflector.Comprises a compact housing containing a transmitter emitting short LED pulses, a photo receiver and a calibrated, oscillating quartz generator producing chronologically precise square-wave pulses. A dual-channel oscilloscope is used to measure the time difference between the two signals. Emitted light pulses are returned by an internal reflector and by a triple-prism reflector placed a long distance from the light source.