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 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 goniophotometer types A, B, and C defined here are derived from publication "CIE 70" of the International Commission on Illumination.^[4]

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.^[5] The axis radiation of lamp and the horizontal of rotating supporter is coaxial.

Camera-based goniophotometers

Luminous intensity distributions can also be measured using imaging goniophotometers.^[6] In order to measure the full angular distribution of a light source, the fisheye camera method can be used. The method is based on employing a fisheye-lens camera installed into a port of an integrating sphere. The camera simultaneously records the luminous intensity data for all angles of light emission, reducing the measurement uncertainty due to temporal effects, such as drift and temporal modulation of the light source. The instantaneous nature of the camera measurement also significantly reduces the time required to obtain the luminous intensity distribution of the device under test, and is not affected by the angular resolution set for the measurement.

See also

• Integrating sphere
• Goniometer
• Goniophotometry
• EULUMDAT

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. S2CID 108700502.
3. Palmer, James (2010). The Art of Radiometry. Bellingham, Washington: SPIE. p. 27. ISBN 9780819472458.
4. CIE 70, The Measurement of Absolute Luminous Intensity Distributions. Vienna: CIE. 1987.
5. "LM-79 Moving Detector Type C Goniophotometer - LISUN". www.lisungroup.com.
6. "US Patent for Differential goniophotometer Patent (Patent # 9,958,317 issued May 1, 2018) - Justia Patents Search". patents.justia.com. Retrieved 2023-05-17.