Abstract
We will discuss about the origin and description of an integrating sphere, the various coatings used along with other significant considerations and the application of an integrating sphere in research and production. It is with this explanation we trust that will inspire you to seek further knowledge on the use of these devices.
Integrating Spheres: Basic Understanding
The work of R. Ulbricht(1849-1923) brought into use on a practical level in the early 1900’s the implementation of the Integrating Sphere in photometry and radiometry. It is basically a hollow sphere with small holes that has on its interior a white coating material that acts as a light diffuser. The holes act as entrance or exit ports for light and the diffuser coating acts as a uniform scattering device.
The purpose is to accurately measure light without regard to the original direction of the light source, beam shape, incident direction or position. Since the light hits all points on the sphere this scattering effect is a summation of all the light in every direction. The result is an accurate measurement of the light wave’s intensity.
Different Coatings Used
Because of the use of ports or baffles for the introduction of light into the sphere, these create deficiencies on the surface of the sphere resulting in erroneousness measurements. Consequently, the use of the highest reflective coating is necessary to overcome these imperfections. Some common coatings are diffused gold, Polytetrafluoroethylene (PTFE) and Barium Sulfate.
Diffused gold is used is infra-red and near infra-red applications. PTFE is used in situations that require extreme abuse such as underwater exploration or extreme temperature environments. Barium Sulfate is a good all-around substance for most applications of radiation energy measurements.
Lastly, the use of flat black is used to absorb most of the light to simulate an open port. It is opposite of highly reflective material and intuitively would not make much sense to use in an integrating sphere. However, it simulates an open port to reduce the introduction of ambient light waves.
Considerations
The size of the integrated sphere has to be a minimum of 1.5 times larger than any device mounted within the sphere. These include the light source and detector.
When using ports, they should not exceed more than 5% of the surface of the inside of the sphere. The reason for this is each device or port represents an interruption in the diffusion properties of the integrating sphere resulting in inaccurate measurements.
Basically, there are three things that determine how efficient an integrating sphere is in measurement capability. These are the physical size of the sphere, the quantity of ports used and the internal coating used in the sphere.
It is the proper combination of these three concepts along with the application in which the integrating sphere is to be used that determine how useful the device will be.
Electro-optical Systems Applications
Some of the applications of integrating spheres are for color measurements, lamp measurements in photometry, fluorescence research, laser and LED measurements, uniform light sources, and samples of specular or scattering reflectance.
Integrating spheres are commercially manufactured for scientific research and development of various products.
