A Goniophotometer is a device used for measurement of the light emitted from an object at different angles. The use of goniophotometers has been increasing in recent years with the introduction of

LED A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

-light sources, which are mostly directed light sources, where the spatial distribution of light is not homogeneous. If a light source is homogeneous in its distribution of light, it is called a Lambertian source. Due to strict regulations, the spatial distribution of light is of high importance to

automotive lighting Automotive lighting is functional exterior lighting in vehicles. A motor vehicle has lighting and signaling devices mounted to or integrated into its front, rear, sides, and, in some cases, top. Various devices have the dual function of illumin ...

and its design.

Uses

A goniophotometer can be used for various applications: * Measurement of

luminous flux In photometry, luminous flux or luminous power is the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of electromagnetic radiation (including infrared, ultraviolet, and visible light), in that ...

of a light source * Measurement of

luminous intensity In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the huma ...

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 The International Commission on Illumination (usually abbreviated CIE for its French name Commission internationale de l'éclairage) is the international authority on light, illumination, colour, and colour spaces. It was established in 1913 a ...

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.

Camera-based goniophotometers

Luminous intensity distributions can also be measured using imaging goniophotometers. 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.

References

Photometry Lighting {{optics-stub