Light speed measurement

A desktop apparatus for the accurate determination  of the speed of light in free propagation.

  • Quick installation: 45 seconds for connecting the cables to the control unit and the power supply to the mains socket.
  • Fully autonomous: it does not require any instrumentation or auxiliary optical components such as oscilloscopes, computers, data loggers, function or pulse generators, power supplies, lenses, supports, etc.
  • Nothing to align: apparatus immediately ready to perform measurements.
  • No small detachable and easily loose part.
  • Determination of the speed of light c in free propagation by measuring the space traveled by light by means of the modulation of a laser beam at a frequency of 433.9 MHz and of the detection of the phase of the optical signal received at a certain distance. It is the shortest of all existing commercial equipment: 70 cm.
  • Direct determination of the speed of light c in transparent or almost transparent solids in the form of bars a few centimeters long, with the ends approximately flat-parallel and glossy, as well as in liquids and their solutions contained in test cells with a volume of about 10 cm3. The cell is supplied with the equipment.
  • Determination of the relative refractive index n of solids or transparent or almost transparent liquids following the definition: n = c / v.
  • Determination of the propagation velocity of the signals in cables and of the dielectric constant of their dielectric. A test cable is provided.
  • Display suitable for a large audience.
  • High accuracy on single measurement: a relative uncertainty less than 0.01, which can be reduced with the use of standard measurement techniques.
  • The working principle is simple and intuitive.


  • measurement of light speed
  • measurement of refraction index
  • measurement of signal speed in coax cables

  • Pulser
  • sliding transmitter
  • sliding receiver
  • graduated track
  • cables
  • glass sample
  • liquid sample holder

  • Transportable version, for demonstrations in the classroom, for exhibitions and for measurements by the students.
  • Small-sized packaging for convenient transportation. The optical bench is 140 cm long and housed in a cylindrical container of 8 cm in diameter, the other component parts in a sturdy cardboard container easily handled.
  • Total weight including the optical bench about 2 Kg.

liquid sample