The goniometer types A / B / C

The luminous intensity distribution of lamps and luminaires is measured in a series of different planes. The number of distribution curves for luminous intensity and the selection of specific measuring planes depend on the light source and the goniophotometer type. A distinction is drawn between the 1, 2, and 3 goniometer type on the basis of CIE Publication no. 70. This is frequently also designated in accordance with the measuring planes A, B, or C.

Typ A Goniophotometer

Type A goniophotometer:

Fixed horizontal axis and moving axis perpendicular to this axis. The measurements are performed by rotating the light source about the horizontal axis, while the other axis is maintained in a fixed position (rotation versus elevation).

Type B goniophotometer

Type B goniophotometer:

Fixed vertical axis and moving horizontal axis. The measurements are performed by rotating the light source about the vertical axis, while the other axis is maintained in a fixed position (elevation versus rotation).

Type C goniophotometer

Type C goniophotometer:

Fixed vertical axis, moving horizontal axis. Measurements are performed in the C-plane or on conical surfaces. Type C corresponds to type B, if the light source is rotated by 90°.

The areas of application can be categorized as follows:

  • Type A goniophotometers are usually deployed for automotive exterior lighting and other directed light sources (variable message signs, runway and taxiway lighting, etc.).
  • Type B goniophotometers are also suitable for these light sources, although the test results are usually converted to Type A coordinates. However, they are also appropriate for street, floodlight and recessed ground luminaires
  • Type C goniophotometers are used for products in general lighting which all have asymmetrical light distribution.