What Is an Integrating Sphere?

An integrating sphere is a device used to test and measure certain properties of a light source. The light is uniformly diffused over the entire surface of the inside of the sphere by means of a highly reflective coating with an equally high degree of diffusion. This diffusion allows for measurement of properties which could not be otherwise observed or measured. It also may be used as a means of providing uniform illumination of a test sample for other purposes, such as research and photography.

Many different designs of integrating spheres are used by laboratories, researchers, quality control technicians, and consumer goods testing organizations, among others. They may be very small models, capable of being held in one hand, or as large as 6.5 feet (2 meters) or more in diameter. Regardless of size and design particulars, a typical integrating sphere has certain basic features. An aperture for a light source and a place to mount optical detectors or other instruments are standard. Some models may be capable of accepting multiple light sources that may be used singly or in tandem as well as having multiple instrumentation mounts.

Baffles are another common feature of an integrating sphere. A baffle is a small physical barrier that prevents direct light radiation from passing from the source directly to the detector or other instruments.

Integrating spheres have an interior coat composed of one of several materials that both reflect and diffuse light. By introducing a light source into such a hollow sphere, the light is diffused and reflected multiple times until its intensity is essentially equal at any point within the sphere. The coating of an integrating sphere depends upon the wavelengths of light it is designed to reflect, such as visible, ultraviolet, or infrared light.

The properties of diffusion and reflection resulting in uniform light intensity make an integrating sphere a useful tool for testing light sources, such as lasers or other lights, and determining a great deal of information about their total power, intensity, and efficiency. An integrating sphere is also useful for testing sample materials. By using a light source with known parameters, it is possible to accurately measure the reflectivity, absorption, and diffusion properties of a sample.