Introduction
Spheres have a broad array of applications in photometry. In most applications, these versatile optical elements are used together with other electro optical devices such as photometers and radiometers. In a research laboratory, an integrating sphere can be used in the measurement of transmittance or reflectance of materials. Spheres are also commonly used in calibration of electronic imaging devices and light measurement.
Measurement of total flux
The total luminous flux produced by a source such as a lamp is measured by placing the source inside the optical element. Rays of light are reflected multiple times by the walls of the sphere until they are detected by the photodetector. This photometric concept is widely used in industries to compare the lumen output of light sources for manufacturing quality control. Other essential elements required for this configuration include a photopic response detector and a diffuser.
Measurement of spectral radiant flux
To measure the spectral radiant flux produced by a source, an integrating sphere is used together with a spectro-radiometer. The configuration is the same as that for measuring total luminous flux except that a photodetector is replaced with a spectro-radiometer. In addition, this set up is suitable for measuring color rendering indices, correlated color temperature, and chromaticity coordinates.
Testing imaging sensors
The port of a sphere allows this optical element to be used as a uniform source diffuse. The uniform irradiance from the diffuse source can be used to test imaging systems such as CCD cameras or array detectors. A set up for such an application is achieved by placing lamps inside a sphere. The lamps are selected depending on the desired radiance. For this configuration, a detector is not needed.
Laser power measurements
Spheres are widely used in labs and industries for laser power measurements. These optical elements are suitable for testing both high and low power industrial lasers. Correct use of baffles when carrying out laser power measurements helps to prevent the direct view of a laser’s hotspot. Spatial integration makes an integrating sphere a suitable choice for testing laser diodes and other devices that exhibit non symmetrical and divergent characteristics. Furthermore, the high reflectivity of a sphere’s coating helps to protect the surface material from extreme heating.
Testing solid-state lighting products
The performance characteristics of LED lamps and other solid state lighting products are obtained by testing and evaluating the luminous efficacy and the total luminous flux produced by the source. Precise measurements of colorimetric data and total luminous flux can be obtained by using an integrating sphere. Although these optical elements enable accurate measurement of the mentioned parameters, they are not capable of measuring spatial distribution of light beams. To measure performance characteristics of these light sources, spheres are mostly used together with gonio-photometers. Gonio-photometers allow accurate measurement of spatial distribution.