Goniophotometer

A Goniophotometer is a device used for measurement of the light emitted from an object at different angles.[1] The use of goniophotometers has been increasing in recent years with the introduction of LED-light sources, which are mostly directed light sources, where the spatial distribution of light is not homogeneous.[2] If a light source is homogeneous in its distribution of light, it is called a Lambertian source.[3] Due to strict regulations, the spatial distribution of light is of high importance to automotive lighting and its design.

Manual (1), and Mitscherlich's optical (2) goniometers for use in crystallography, c. 1900

Uses

A goniophotometer can be used used for various applications:

  • Measurement of luminous flux of a light source
  • Measurement of luminous intensity distribution from a source much smaller than the size of the goniophotometer

Equipped with color sensors additional characteristics can be measured

  • Distribution of correlated color temperature
  • Color uniformity

Types

The various types of goniophotometer are defined here[4] which is derive from publication "CIE 70" from the International Commission on Illumination.[5]

Type A

Fixed horizontal axis, with the vertical axis attached, both perpendicular to the main output direction of the light source

Type B

Fixed vertical axis, with the horizontal axis attached, both perpendicular to the main output direction of the light source

Type A and B are Double columns structure. This type is applied to fixed the grille lamp. The symmetry axis of lamp and the horizontal of rotating supporter is coaxial, in the B-βcoordinate system, and the two is vertical Cross, in the A-αcoordinate system.

Type C

Fixed vertical axis perpendicular to the line of measurement, with a horizontal axis parallel to the main output direction of the light source

Type C are single column structures. The single column structure is created when the assistant column is taken down from double columns structure. This type is applied to a fixed tube lamp, spot lamp, or other devices. The axis radiation of lamp and the horizontal of rotating supporter is coaxial.

See also

References
  1. Marx, P. (1997). "New goniophotometers for light-engineering laboratories" (PDF). Light & Engineering. 5 (4): 32–36.
  2. Lindemann, Matthias; Maass, Robert (15 December 2009). "Photometry and colorimetry of reference LEDs by using a compact goniophotometer". MAPAN. 24 (3): 143–152. doi:10.1007/s12647-009-0018-6.
  3. Palmer, James (2010). The Art of Radiometry. Bellingham, Washington: SPIE. p. 27. ISBN 9780819472458.
  4. "The goniometer types A / B / C". http://www.optronik.de. Retrieved 11 November 2015. External link in |publisher= (help)
  5. CIE 70, The Measurement of Absolute Luminous Intensity Distributions. Vienna: CIE. 1987.


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